ATOMS Ancient Greece to Now. DEFINED Atom (n.)- A unit of matter, the smallest unit of an element, consisting of a dense, central, positively charged

ATOMSATOMS

Ancient Greece to NowAncient Greece to Now

DEFINEDDEFINED Atom (n.)- A unit of matter, the smallest Atom (n.)- A unit of matter, the smallest

unit of an element, consisting of a dense, unit of an element, consisting of a dense, central, positively charged nucleus central, positively charged nucleus surrounded by a system of electrons, surrounded by a system of electrons, equal in number to the number of nuclear equal in number to the number of nuclear protons, and characteristically remaining protons, and characteristically remaining undivided in chemical reactions except undivided in chemical reactions except for limited removal, transfer, or exchange for limited removal, transfer, or exchange of certain electrons.of certain electrons.

THE GREEK ATOMISTS THE GREEK ATOMISTS The word "atom" comes from the The word "atom" comes from the

Greek "Greek "atomosatomos" and signifies " and signifies "indivisible" or “Not to be cut”. "indivisible" or “Not to be cut”.

THE GREEK ATOMISTSTHE GREEK ATOMISTS Leucippus Leucippus of Milet invented this of Milet invented this

notion in 420 B.C. His disciple, notion in 420 B.C. His disciple, DemocritusDemocritus of Abdere (around 460- of Abdere (around 460-370 BC.), asked this question: If you 370 BC.), asked this question: If you break a piece of matter in half, and break a piece of matter in half, and then break it in half again, how many then break it in half again, how many breaks will you have to make before breaks will you have to make before you can break it no further? you can break it no further?

THE GREEK ATOMISTSTHE GREEK ATOMISTS Democritus thought that it ended at Democritus thought that it ended at

some point, a smallest possible bit of some point, a smallest possible bit of matter. He explained that matter matter. He explained that matter was made up of particles in was made up of particles in perpetual motion and endowed with perpetual motion and endowed with ideal qualities: ideal qualities:

Democritus’ Atomic TheoryDemocritus’ Atomic Theory invisible because of their extremely invisible because of their extremely

small size small size indivisible as their name indicates indivisible as their name indicates solid (no void inside) solid (no void inside)

Democritus’ Atomic TheoryDemocritus’ Atomic Theory eternal because they are perfect eternal because they are perfect surrounded by an empty space (to surrounded by an empty space (to

explain their movement and changes explain their movement and changes in density) in density)

having an infinite number of having an infinite number of shapes (to explain the diversity shapes (to explain the diversity observed in nature) observed in nature)

End of Atoms???End of Atoms??? Unfortunately, the atomic ideas of Unfortunately, the atomic ideas of

Democritus had no lasting effects on Democritus had no lasting effects on other Greek philosophers, including other Greek philosophers, including AristotleAristotle. .

Aristotle dismissed the atomic idea Aristotle dismissed the atomic idea as worthless. as worthless.

AristotleAristotle Aristotle believed that matter was Aristotle believed that matter was

made up of only four elements (the made up of only four elements (the Four Element TheoryFour Element Theory) fire, air, ) fire, air, earth, and water. People considered earth, and water. People considered Aristotle’s opinions very important Aristotle’s opinions very important and if Aristotle thought the atomic and if Aristotle thought the atomic idea had no merit, then most other idea had no merit, then most other people thought the same also people thought the same also

AristotleAristotle For more 2000 years nobody did For more 2000 years nobody did

anything to continue the explorations anything to continue the explorations that the Greeks had started into the that the Greeks had started into the nature of matter.nature of matter.

THE ALCHEMY OF THE MIDDLE THE ALCHEMY OF THE MIDDLE AGESAGES

Originating in the Middle Ages, Originating in the Middle Ages, alchemy was born from the progress alchemy was born from the progress of metallurgy and from the of metallurgy and from the inadequacy of the theory of the 4 inadequacy of the theory of the 4 elements for representing the elements for representing the diversity of matter. diversity of matter.


The "The "grandgrand planplan" of alchemy was to " of alchemy was to achieve the transmutation of lowly metals achieve the transmutation of lowly metals (like copper) into "noble" metals such as (like copper) into "noble" metals such as gold. Without doubt because the success gold. Without doubt because the success of such "Grand Works" (transmutation) of such "Grand Works" (transmutation) opened up prospects of wealth and power, opened up prospects of wealth and power, the activities of alchemists were the activities of alchemists were surrounded by secrecy and were surrounded by secrecy and were performed using extremely ancient performed using extremely ancient processes of the esoteric and of the occult. processes of the esoteric and of the occult.


In spite of their esoteric beliefs, In spite of their esoteric beliefs, alchemists developed the alchemists developed the observation, experimentation, observation, experimentation, measurement and classification of measurement and classification of the elements: alchemy is therefore a the elements: alchemy is therefore a respectable precursor of chemistry. respectable precursor of chemistry.


Anyway, don't forget that Newton Anyway, don't forget that Newton was adept at alchemy and that was adept at alchemy and that today's physics has turned the old today's physics has turned the old dream of transmutation into reality dream of transmutation into reality by transforming certain atoms into by transforming certain atoms into other atoms other atoms

1803 John Dalton - first modern 1803 John Dalton - first modern atomic theoryatomic theory

1799 Joseph Louis Proust - Law of 1799 Joseph Louis Proust - Law of Definite Proportions (matter Definite Proportions (matter combines in a definite proportion combines in a definite proportion consistently) consistently)

Dalton - Law of Multiple Proportions Dalton - Law of Multiple Proportions (matter combines in small, fixed, (matter combines in small, fixed, whole number ratios) whole number ratios)


Dalton applied these ideas to form Dalton applied these ideas to form his "atomic theory" his "atomic theory"

*Atoms are small, indivisible spheres *Atoms are small, indivisible spheres *Atoms of a given element are *Atoms of a given element are

identical identical


*Atoms cannot be created, destroyed *Atoms cannot be created, destroyed or transformed or transformed

*Compounds are the results of small *Compounds are the results of small whole number ratios of atoms whole number ratios of atoms

*Relative numbers and kinds of *Relative numbers and kinds of atoms in a compound are constant atoms in a compound are constant

DISCOVERY OF NATURAL DISCOVERY OF NATURAL RADIATIONRADIATION

On November 8, 1895, at the On November 8, 1895, at the University of Würzburg, University of Würzburg, Wilhelm Wilhelm Roentgen’sRoentgen’s attention was drawn to attention was drawn to a glowing fluorescent screen on a a glowing fluorescent screen on a nearby table.nearby table.


Roentgen immediately determined Roentgen immediately determined that the fluorescence was caused by that the fluorescence was caused by invisible rays originating from the invisible rays originating from the partially evacuated glass Hittorf-partially evacuated glass Hittorf-Crookes tube he was using to study Crookes tube he was using to study cathode rays (i.e., electrons). cathode rays (i.e., electrons).


Surprisingly, these mysterious rays Surprisingly, these mysterious rays penetrated the opaque black paper penetrated the opaque black paper wrapped around the tube. Roentgen wrapped around the tube. Roentgen had discovered had discovered X- raysX- rays, a , a momentous event that instantly momentous event that instantly revolutionized the field of physics revolutionized the field of physics and medicine. and medicine.


However, prior to his first formal However, prior to his first formal correspondence to the University correspondence to the University Physical-Medical Society, Roentgen Physical-Medical Society, Roentgen spent two months thoroughly spent two months thoroughly investigating the properties of X investigating the properties of X rays. For his discovery, Roentgen rays. For his discovery, Roentgen received the first Nobel Prize in received the first Nobel Prize in physics in 1901. physics in 1901.


He rejected a title (i.e., von He rejected a title (i.e., von Roentgen) that would have provided Roentgen) that would have provided entry into the German nobility, and entry into the German nobility, and donated the money he received from donated the money he received from the Nobel Prize to his University. the Nobel Prize to his University.


Roentgen did accept the honorary Roentgen did accept the honorary degree of Doctor of Medicine offered degree of Doctor of Medicine offered to him by the medical faculty of his to him by the medical faculty of his own University of Würzburg. own University of Würzburg.

However, he refused to take out any However, he refused to take out any patents in order that the world could patents in order that the world could freely benefit from his work. At the freely benefit from his work. At the time of his death, Roentgen was time of his death, Roentgen was nearly bankrupt from the inflation that nearly bankrupt from the inflation that followed WW I. followed WW I.


One day in 1896, One day in 1896, Henri BecquerelHenri Becquerel (by chance according to legend?) (by chance according to legend?) arranged in his cupboard, a packet of arranged in his cupboard, a packet of uranium salt beside an unexposed uranium salt beside an unexposed photographic plate. Several days photographic plate. Several days later, he took out the plate later, he took out the plate and developed it. and developed it.


To his surprise, he noticed that the To his surprise, he noticed that the photographic plate had been photographic plate had been exposed without having been exposed without having been exposed to the light. Having exposed to the light. Having repeated this experiment, he repeated this experiment, he concluded that Uranium concluded that Uranium spontaneously emits what he called spontaneously emits what he called "uranic rays"."uranic rays".


Marie and Pierre CurieMarie and Pierre Curie, together, , together, began investigating the phenomenon began investigating the phenomenon of radioactivity recently discovered in of radioactivity recently discovered in uranium ore, uranium ore, pitchblendepitchblende. In 1898, . In 1898, Marie Curie discovered after Marie Curie discovered after chemical extraction of uranium from chemical extraction of uranium from the ore, the residual material was the ore, the residual material was more "active" than the pure uranium. more "active" than the pure uranium.


Pitchblende emits more radiation Pitchblende emits more radiation than uranium itself. She deduced than uranium itself. She deduced that this ore contains, in very small that this ore contains, in very small quantities, one or more elements quantities, one or more elements much more active that uranium. much more active that uranium.


With the assistance of her husband Pierre With the assistance of her husband Pierre Curie (shortly after his marriage to Marie in Curie (shortly after his marriage to Marie in 1895, Pierre subjugated his research to her 1895, Pierre subjugated his research to her interests.) and after two years of effort, she interests.) and after two years of effort, she arrived at isolating two new elements: arrived at isolating two new elements: PoloniumPolonium (named thus in tribute to her (named thus in tribute to her homeland) and homeland) and RadiumRadium. .

It took four more years of processing tons of It took four more years of processing tons of ore under oppressive conditions to isolate ore under oppressive conditions to isolate enough of each element to determine its enough of each element to determine its chemical properties. chemical properties.


Although Henri Becquerel discovered the Although Henri Becquerel discovered the phenomenon, Marie coined the term phenomenon, Marie coined the term ““radioactivityradioactivity”. For their work on ”. For their work on radioactivity, the Curies were awarded the radioactivity, the Curies were awarded the 1903 Nobel Prize in physics. 1903 Nobel Prize in physics.

Marie was awarded the 1911 Nobel Prize Marie was awarded the 1911 Nobel Prize in chemistry for her discoveries of radium in chemistry for her discoveries of radium and polonium, thus becoming the first and polonium, thus becoming the first person to receive two Nobel Prizes. person to receive two Nobel Prizes.

For the remainder of her life she tirelessly For the remainder of her life she tirelessly investigated and promoted the use of investigated and promoted the use of radium as a treatment for cancer.radium as a treatment for cancer.

DISCOVERY OF THE ELECTRON DISCOVERY OF THE ELECTRON

In 1897, In 1897, J.J. ThompsonJ.J. Thompson discovered discovered the first component part of the atom: the first component part of the atom: the the electronelectron, a particle with a , a particle with a negative electric charge. negative electric charge.

DISCOVERY OF THE ELECTRONDISCOVERY OF THE ELECTRON

In 1904, he proposed In 1904, he proposed an initial model of an an initial model of an atom, since atom, since nicknamed "the plum nicknamed "the plum pudding model". He pudding model". He imagined the atom as imagined the atom as a sphere full of an a sphere full of an electrically positive electrically positive substance mixed with substance mixed with negative electron "like negative electron "like the plums in a the plums in a pudding" pudding"

QUANTAQUANTA In 1900 In 1900 Max PlanckMax Planck, a , a

professor of theoretical professor of theoretical physics in Berlin physics in Berlin showed that when you showed that when you vibrate atoms strong vibrate atoms strong enough, such as when enough, such as when you heat an object you heat an object until it glows, it emits until it glows, it emits radiation in separate radiation in separate bursts of energy. He bursts of energy. He called these energy called these energy bursts bursts quantaquanta. .

QUANTAQUANTA Physicists at the time thought that Physicists at the time thought that

light consisted of waves. But the light consisted of waves. But the quanta behaved like particles and, in quanta behaved like particles and, in turn, these particles of light received turn, these particles of light received the name photons. Atoms not only the name photons. Atoms not only emit photons, but they can also emit photons, but they can also absorb them. absorb them.

QUANTAQUANTA Any list of the greatest Any list of the greatest

thinkers in history thinkers in history contains the name of contains the name of the brilliant physicist the brilliant physicist Albert EinsteinAlbert Einstein. His . His theories of relativity led theories of relativity led to entirely new ways of to entirely new ways of thinking about time, thinking about time, space, matter, energy, space, matter, energy, and gravity. Einstein and gravity. Einstein won his only Nobel Prize won his only Nobel Prize for physics in 1908 for for physics in 1908 for discovering that light discovering that light absorption can release absorption can release electrons from atoms. electrons from atoms.

QUANTAQUANTA This phenomenon has the name This phenomenon has the name

““photoelectric effectphotoelectric effect”. A heated ”. A heated controversy occurred for many years controversy occurred for many years on deciding whether light consisted on deciding whether light consisted of waves or particles. The evidence of waves or particles. The evidence appeared strong for both cases. appeared strong for both cases.

QUANTAQUANTA Later, physicists showed that light Later, physicists showed that light

appears as either wave-like or particle-appears as either wave-like or particle-like (but never both at the same time) like (but never both at the same time) depending on the experimental setup. depending on the experimental setup. This is called the dual nature of light. He This is called the dual nature of light. He also showed that energy and mass were also showed that energy and mass were interconvertible. His famous equation interconvertible. His famous equation E=mc2 related energy and mass. E= E=mc2 related energy and mass. E= energy, m=mass, c=speed of light. energy, m=mass, c=speed of light.

Oil Drop ExperimentOil Drop Experiment Robert AndrewsRobert Andrews Millikan, Millikan, (1868–(1868–

1953) was a U.S. physicist who made 1953) was a U.S. physicist who made the first determination of the charge the first determination of the charge of the electron by using his famous of the electron by using his famous ““oil drop experimentoil drop experiment”. For these ”. For these achievements, he was awarded the achievements, he was awarded the 1923 Nobel Prize for Physics.1923 Nobel Prize for Physics.

DISCOVERY OF THE NUCLEUS DISCOVERY OF THE NUCLEUS

In 1912, In 1912, Ernest RutherfordErnest Rutherford (New (New Zealand physicist) discovered the Zealand physicist) discovered the atomic nucleus. atomic nucleus.

Using his famous “Using his famous “gold foil gold foil experimentexperiment”, Rutherford used alpha ”, Rutherford used alpha particles to bombard atoms. particles to bombard atoms.

DISCOVERY OF THE NUCLEUSDISCOVERY OF THE NUCLEUS

He used radium as the source of the He used radium as the source of the alpha particles and shined them onto alpha particles and shined them onto the atoms in gold foil. Behind the the atoms in gold foil. Behind the screen sat a fluorescent screen for screen sat a fluorescent screen for which he could observe the alpha which he could observe the alpha particles impact. The results of the particles impact. The results of the experiment were unexpected. experiment were unexpected.


Most of the alpha particles went Most of the alpha particles went smoothly through the foil. Only an smoothly through the foil. Only an occasional alpha veered sharply from occasional alpha veered sharply from its original path, sometimes bouncing its original path, sometimes bouncing straight back from the foil. This straight back from the foil. This surprised Rutherford so much he said surprised Rutherford so much he said it was like firing a cannon at a sheet it was like firing a cannon at a sheet of tissue paper and having the shell of tissue paper and having the shell bounce back to you. bounce back to you.


Rutherford reasoned that the alpha Rutherford reasoned that the alpha particles must get scattered by tiny particles must get scattered by tiny bits of positively charged matter. His bits of positively charged matter. His new model of the atom showed that new model of the atom showed that its positive electric charge and the its positive electric charge and the majority of its mass were majority of its mass were concentrated in an almost point sized concentrated in an almost point sized nucleus. nucleus.


Rutherford thought most of the Rutherford thought most of the space around the positive center had space around the positive center had nothing in it. It is worth noting that in nothing in it. It is worth noting that in contrast to the atom of the Greeks, contrast to the atom of the Greeks, Rutherford's is neither indivisible Rutherford's is neither indivisible (because it's a composite structure), (because it's a composite structure), nor is it solid as it contains mostly nor is it solid as it contains mostly empty space. empty space.


It was not until 1919 that Rutherford It was not until 1919 that Rutherford finally identified the particles in the finally identified the particles in the nucleus with the discrete positive nucleus with the discrete positive charges. He named them protons, charges. He named them protons, from the Greek for first, because they from the Greek for first, because they were the first identified building were the first identified building blocks of the nuclei. He found the blocks of the nuclei. He found the protons mass was 1,836 times greater protons mass was 1,836 times greater than the mass of the electron.than the mass of the electron.


DISCOVERY OF NUCLEONS DISCOVERY OF NUCLEONS Rutherford understood that the Rutherford understood that the

nucleus is itself composed of nucleus is itself composed of nucleons. These nucleons are of two nucleons. These nucleons are of two types: types:

Positively charged, it's a proton. Positively charged, it's a proton. Neutrally charged, it's a neutron Neutrally charged, it's a neutron

DISCOVERY OF NUCLEONSDISCOVERY OF NUCLEONS James ChadwickJames Chadwick effectively discovered effectively discovered

the neutron in 1932. the neutron in 1932.

Moseley, Proton and atomic Moseley, Proton and atomic numbernumber

Henry Gwyn JeffreysHenry Gwyn Jeffreys Moseley, Moseley, (1887–1915) was a British physicist (1887–1915) was a British physicist who first established the atomic who first established the atomic numbers of the elements by studying numbers of the elements by studying their X-ray spectra. This led to a their X-ray spectra. This led to a complete classification of the elements, complete classification of the elements, and also provided an experimental and also provided an experimental basis for an understanding of the basis for an understanding of the structure of the atom. structure of the atom.


All atoms are characterized by their All atoms are characterized by their Atomic NumberAtomic Number represented by represented by ZZ: : this is the number of protons in the this is the number of protons in the atom. For example, for hydrogen Z = atom. For example, for hydrogen Z = 1, for carbon Z = 6, for uranium Z = 1, for carbon Z = 6, for uranium Z = 92 etc. 92 etc.


For a neutral atom, the number of For a neutral atom, the number of protons Z is equal to the number of protons Z is equal to the number of electrons because the - charge of an electrons because the - charge of an electron cancels out the + charge of electron cancels out the + charge of a proton. It is the number of protons a proton. It is the number of protons Z that defines an atom. Z that defines an atom.

BOHRS ATOM BOHRS ATOM In order to take account of atomic In order to take account of atomic

stability, in 1913 stability, in 1913 Niels BohrNiels Bohr created created a new model of the atom: the a new model of the atom: the Electron Shell Model, or Solar Electron Shell Model, or Solar System ModelSystem Model. .

BOHRS ATOMBOHRS ATOM This model explained why electrons’ This model explained why electrons’

negative charge did not spiral toward negative charge did not spiral toward the nucleus’ positive charge.the nucleus’ positive charge.The orbits of the electrons can't be just The orbits of the electrons can't be just anywhere but are "quantified"; only anywhere but are "quantified"; only certain particular orbits are permitted certain particular orbits are permitted for the electron. It's not until one for the electron. It's not until one jumps from one orbit to another that it jumps from one orbit to another that it can emit (or absorb) light.can emit (or absorb) light.

What is "classical" and What is "classical" and continuous light ?continuous light ?

Not so easy to represent such an Not so easy to represent such an immaterial concept! immaterial concept! At the end of the 19th century, At the end of the 19th century, James MaxwellJames Maxwell defined light as defined light as being a beam of being a beam of electromagnetic electromagnetic waveswaves moving at a constant speed moving at a constant speed in the vacuum: the famous speed in the vacuum: the famous speed cc of 300,000 kilometers per second. of 300,000 kilometers per second.

Where does light come from?Where does light come from? Quantum physics allows us to better Quantum physics allows us to better

understand how light is emitted by understand how light is emitted by matter... The world of the atom matter... The world of the atom according to Niels Bohr was a model according to Niels Bohr was a model at the frontier of two ages: the at the frontier of two ages: the classical age, pre-quantum and the classical age, pre-quantum and the quantum world. quantum world.

Where does light come from?Where does light come from? This emission is explained then by This emission is explained then by

the jump that an electron makes the jump that an electron makes from an orbit E2 to an orbit E1. from an orbit E2 to an orbit E1. During this jump towards this less During this jump towards this less energetic orbit E1 (an inner orbit), energetic orbit E1 (an inner orbit), the electron will lose part of its the electron will lose part of its energy in the form of a photon energy in the form of a photon emitted outwards. emitted outwards.

Where does light come from?Where does light come from? Each photon of a radiation (light, Each photon of a radiation (light,

radio waves, X rays...) carries a radio waves, X rays...) carries a quantum of energy characteristic of quantum of energy characteristic of its frequency (frequency of visible its frequency (frequency of visible light = color) light = color)

Where does light come from?Where does light come from?

Where does light come from?Where does light come from? The higher the frequency of light, the The higher the frequency of light, the

greater the energy and the more the greater the energy and the more the color will tend towards blue (and color will tend towards blue (and from there towards ultra-violet, X ray from there towards ultra-violet, X ray and Gamma rays). and Gamma rays).


Where does light come from?Where does light come from? An electron, making a "bigger jump" An electron, making a "bigger jump"

from one atomic orbit to another, will from one atomic orbit to another, will then emit a photon correspondingly then emit a photon correspondingly more energetic and of a more energetic and of a correspondingly higher frequency. correspondingly higher frequency.


Where does light come from?Where does light come from? Conversely, an atom's electron could Conversely, an atom's electron could

absorb a photon of a given energy absorb a photon of a given energy and thus jump from a less energetic and thus jump from a less energetic orbit to a more energetic orbit: It will orbit to a more energetic orbit: It will thus become more thus become more excitedexcited than than normal because it is in a more normal because it is in a more energetic orbit. It is in becoming less energetic orbit. It is in becoming less excited that it would subsequently excited that it would subsequently re-emit a photon. re-emit a photon.

The visible spectrum The visible spectrum Each atom can only emit a precise and Each atom can only emit a precise and

characteristic set of colors: Each color characteristic set of colors: Each color of light is in fact a particular frequency of light is in fact a particular frequency (and therefore a level of energy) of a (and therefore a level of energy) of a photon. All of the possible jumps photon. All of the possible jumps between orbits that an electron can between orbits that an electron can make within a given atom translate make within a given atom translate into the emission (or absorption) of a into the emission (or absorption) of a characteristic characteristic spectrum of lightspectrum of light: :

The visible spectrum The visible spectrum Here we have a veritable identity Here we have a veritable identity

card for a given type of atom. It's card for a given type of atom. It's because of this readily identifiable because of this readily identifiable spectrum that we can know which spectrum that we can know which atoms exist in stars in the firmament. atoms exist in stars in the firmament. Their light is captured by telescopes, Their light is captured by telescopes, analyzed and compared with the analyzed and compared with the spectrums of hydrogen, helium etc spectrums of hydrogen, helium etc

The visible spectrumThe visible spectrum

TOWARDS QUANTUM PHYSICSTOWARDS QUANTUM PHYSICS

What an intellectual pleasure (and what What an intellectual pleasure (and what laziness!) to represent atoms in the form laziness!) to represent atoms in the form of little balls turning one around of little balls turning one around another... This model is, moreover, still another... This model is, moreover, still the one that the general public has in the one that the general public has in their heads. In fact this model is false their heads. In fact this model is false because at the atomic scale, new laws because at the atomic scale, new laws apply! These laws are part of a strange apply! These laws are part of a strange physics, very far from our current physics, very far from our current concepts: concepts: quantum physicsquantum physics. .

http://perso.club-internet.fr/molaire1/e_quantic.html

TOWARDS QUANTUM PHYSICS TOWARDS QUANTUM PHYSICS

Bohr's model is the last model obedient to Bohr's model is the last model obedient to classical physics, that is to say physics classical physics, that is to say physics that explains movements and phenomena that explains movements and phenomena in terms of our human scale. These models in terms of our human scale. These models of atoms are therefore easy to understand of atoms are therefore easy to understand and to represent. and to represent.

Since the middle of the 1930s, the Since the middle of the 1930s, the atom has become a mathematical atom has become a mathematical description that is very difficult to description that is very difficult to transcribe into imagestranscribe into images

Wave-particle dualityWave-particle duality Louis VictorLouis Victor de Brogliede Broglie (1892–1987) (1892–1987)

was a French physicist who first was a French physicist who first developed the principle that an electron developed the principle that an electron or any other particle can be considered to or any other particle can be considered to behave as a wave as well as a particle. behave as a wave as well as a particle. This This wave-particle dualitywave-particle duality is a is a fundamental principle governing the fundamental principle governing the structure of the atom, and for its structure of the atom, and for its discovery, de Broglie was awarded the discovery, de Broglie was awarded the 1929 Nobel Prize for Physics. 1929 Nobel Prize for Physics.

Wave-particle dualityWave-particle duality The most important question that The most important question that

quantum physics has been quantum physics has been attempting to address concerns the attempting to address concerns the manner in which to represent manner in which to represent physical objects and their properties. physical objects and their properties.

Wave-particle dualityWave-particle duality The old physics, known as classical, The old physics, known as classical,

distinguished two types of distinguished two types of fundamental entities:fundamental entities: particlesparticles, which are sorts of , which are sorts of

microscopic balls, microscopic balls, waveswaves, which propagate in space a bit , which propagate in space a bit

like the movement of a wave on the sea. like the movement of a wave on the sea.

Wave-particle dualityWave-particle duality Quantum physics doesn't hold on to Quantum physics doesn't hold on to

this classification, convenient as it is. this classification, convenient as it is. The objects which it considers are The objects which it considers are neither particles, nor waves, but neither particles, nor waves, but "something else". "something else".

Wave-particle dualityWave-particle duality The following analogy should help us: The following analogy should help us: Look at a cylinder from two different Look at a cylinder from two different

angles, a cylinder appears angles, a cylinder appears sometimes as a circle, sometimes as sometimes as a circle, sometimes as a rectangle. When in fact it is neither a rectangle. When in fact it is neither one nor the other. one nor the other.

Wave-particle dualityWave-particle duality

Wave-particle dualityWave-particle duality That’s the way the photon, the electron That’s the way the photon, the electron

and all elementary particles are, thus and all elementary particles are, thus the image of a particle is but one facet the image of a particle is but one facet of a more complex entity.of a more complex entity.

De Broglie's discovery of wave-particle De Broglie's discovery of wave-particle duality enabled physicists to view duality enabled physicists to view Einstein's conviction that matter and Einstein's conviction that matter and energy are interconvertible as being energy are interconvertible as being fundamental to the structure of matter. fundamental to the structure of matter.

Wave-particle dualityWave-particle duality The study of matter waves led not The study of matter waves led not

only to a much deeper understanding only to a much deeper understanding of the nature of the atom but also to of the nature of the atom but also to explanations of chemical bonds and explanations of chemical bonds and the practical application of electron the practical application of electron waves in electron microscopes waves in electron microscopes

PAULI'S EXCLUSION PRINCIPLEPAULI'S EXCLUSION PRINCIPLE

This fundamental law of quantum This fundamental law of quantum physics was set out for the first time physics was set out for the first time by the physicist by the physicist Wolfgang PauliWolfgang Pauli in in 1925. 1925.


All of the particles of the same type All of the particles of the same type have an identical nature but can have have an identical nature but can have different properties. different properties.

For example, the electrons in an atom For example, the electrons in an atom have different energies (associated have different energies (associated with their orbits). Each particle thus with their orbits). Each particle thus possesses a certain number of its own possesses a certain number of its own properties that form "the state of the properties that form "the state of the particle". particle".


No two electrons in the same No two electrons in the same atom can have the same set of atom can have the same set of four quantum numbers (energy four quantum numbers (energy level, sublevel, orbital, or spin).level, sublevel, orbital, or spin).


In an atom, two electrons can have In an atom, two electrons can have the same energy on the condition the same energy on the condition that their spins are different. that their spins are different. This This explains the progressive filling explains the progressive filling of the periodic table of of the periodic table of Mendeleev, that is to say the Mendeleev, that is to say the electronic structure of atoms.electronic structure of atoms.

Heisenberg Uncertainty PrincipleHeisenberg Uncertainty Principle

In 1927 Werner Karl Heisenberg In 1927 Werner Karl Heisenberg made the discovery for which he is made the discovery for which he is best known -- that of the best known -- that of the uncertainty principleuncertainty principle. This states . This states that it is that it is impossible to specify impossible to specify precisely both the position and precisely both the position and the simultaneous momentum the simultaneous momentum (mass multiplied by velocity) of a (mass multiplied by velocity) of a particleparticle. .

Heisenberg Uncertainty PrincipleHeisenberg Uncertainty Principle Dare we have a new image to illustrate this Dare we have a new image to illustrate this

principle: principle: Deep in the woods at night, a nature lover Deep in the woods at night, a nature lover hears the hooting of an owl. If he would like, hears the hooting of an owl. If he would like, at the same time, see the feathered at the same time, see the feathered creature, he would have to turn a torch on creature, he would have to turn a torch on him: But then it's a good bet that the him: But then it's a good bet that the surprised owl will stop singing. This gives rise surprised owl will stop singing. This gives rise to the insoluble dilemma: We can't both hear to the insoluble dilemma: We can't both hear and see the owl at the same time... Alas! and see the owl at the same time... Alas!


Therefore electrons are better Therefore electrons are better thought of as occurring in an thought of as occurring in an electron cloudelectron cloud surrounding the surrounding the nucleus than in orbits around the nucleus than in orbits around the nucleus.nucleus.


If it is necessary to risk an image to If it is necessary to risk an image to illustrate this curious phenomena, illustrate this curious phenomena, one could imagine the electron as a one could imagine the electron as a sub-marine which emerges, long sub-marine which emerges, long enough for a measurement, from its enough for a measurement, from its probabilistic ocean.probabilistic ocean.


Later, it submerges and it will be Later, it submerges and it will be impossible to an observer from the impossible to an observer from the surface to localize it with any surface to localize it with any precision: one could do no more that precision: one could do no more that define the volume of the ocean define the volume of the ocean where the submarine could probably where the submarine could probably be found.be found.

Orbitals and orbitsOrbitals and orbits When the a planet moves around the When the a planet moves around the

sun, you can plot a definite path for it sun, you can plot a definite path for it which is called an orbit. A simple which is called an orbit. A simple view of the atom looks similar and view of the atom looks similar and you may have pictured the electrons you may have pictured the electrons as orbiting around the nucleus. The as orbiting around the nucleus. The truth is different, and electrons in truth is different, and electrons in fact inhabit regions of space known fact inhabit regions of space known as as orbitals.orbitals.

Orbitals and orbitsOrbitals and orbits Orbits and orbitals sound similar, but Orbits and orbitals sound similar, but

they have quite different meanings. they have quite different meanings. It is essential that you understand It is essential that you understand the difference between them. the difference between them.

The impossibility of drawing The impossibility of drawing orbits for electronsorbits for electrons

To plot a path for something you To plot a path for something you need to know exactly where the need to know exactly where the object is and be able to work out object is and be able to work out exactly where it's going to be an exactly where it's going to be an instant later. You can't do this for instant later. You can't do this for electrons. electrons.


The The Heisenberg Uncertainty Heisenberg Uncertainty PrinciplePrinciple says - loosely - that you says - loosely - that you can't know with certainty both where can't know with certainty both where an electron is and where it's going an electron is and where it's going next. That makes it impossible to next. That makes it impossible to plot an orbit for an electron around a plot an orbit for an electron around a nucleus. Is this a big problem? No. If nucleus. Is this a big problem? No. If something is impossible, you have to something is impossible, you have to accept it and find a way around it.accept it and find a way around it.


Suppose you had a single hydrogen Suppose you had a single hydrogen atom and at a particular instant atom and at a particular instant plotted the position of the one plotted the position of the one electron. Soon afterwards, you do the electron. Soon afterwards, you do the same thing, and find that it is in a same thing, and find that it is in a new position. You have no idea how new position. You have no idea how it got from the first place to the it got from the first place to the second.second.


You keep on doing this over and over You keep on doing this over and over again, and gradually build up a sort again, and gradually build up a sort of 3D map of the places that the of 3D map of the places that the electron is likely to be found.electron is likely to be found.


95% of the time (or any other 95% of the time (or any other percentage you choose), the electron percentage you choose), the electron will be found within a fairly easily will be found within a fairly easily defined region of space quite close to defined region of space quite close to the nucleus. Such a region of space the nucleus. Such a region of space is called an is called an orbital.orbital. You can think of You can think of an orbital as being the region of an orbital as being the region of space in which the electron lives.space in which the electron lives.


What is the electron doing in the What is the electron doing in the orbital? We don't know, we can't orbital? We don't know, we can't know, and so we just ignore the know, and so we just ignore the problem! All you can say is that if an problem! All you can say is that if an electron is in a particular orbital it electron is in a particular orbital it will have a particular definable will have a particular definable energy.energy.

OrbitalsOrbitals Each orbital has a name.Each orbital has a name. The orbital occupied by the hydrogen The orbital occupied by the hydrogen

electron is called a electron is called a 1s orbital.1s orbital. The The "1""1" represents the fact that the orbital is in the represents the fact that the orbital is in the energy level closest to the nucleus. The energy level closest to the nucleus. The "s""s" tells you about the shape of the orbital. s tells you about the shape of the orbital. s orbitals are spherically symmetric around orbitals are spherically symmetric around the nucleus - in each case, like a hollow the nucleus - in each case, like a hollow ball made of rather chunky material with ball made of rather chunky material with the nucleus at its center.the nucleus at its center.

s orbitals orbital The orbital on the The orbital on the

left is a left is a 2s orbital.2s orbital. This is similar to a This is similar to a 1s orbital except 1s orbital except that the region that the region where there is the where there is the greatest chance of greatest chance of finding the electron finding the electron is further from the is further from the nucleus - this is an nucleus - this is an orbital at the second orbital at the second energy level.energy level.

s orbitals orbital If you look carefully, If you look carefully,

you will notice that you will notice that there is another region there is another region of slightly higher of slightly higher electron density (where electron density (where the dots are thicker) the dots are thicker) nearer the nucleus. nearer the nucleus. ("Electron density" is ("Electron density" is another way of talking another way of talking about how likely you about how likely you are to find an electron are to find an electron at a particular place.)at a particular place.)

s orbitals orbital 2s (and 3s, 4s, etc) 2s (and 3s, 4s, etc)

electrons spend some electrons spend some of their time closer to of their time closer to the nucleus than you the nucleus than you might expect. The might expect. The effect of this is to effect of this is to slightly reduce the slightly reduce the energy of electrons in energy of electrons in s orbitals. s orbitals. The nearer The nearer the nucleus the the nucleus the electrons get, the electrons get, the lower their energylower their energy. .

p orbitalsp orbitals Not all electrons inhabit s orbitals (in Not all electrons inhabit s orbitals (in

fact, very few electrons live in s fact, very few electrons live in s orbitals). At the first energy level, the orbitals). At the first energy level, the only orbital available to electrons is only orbital available to electrons is the 1s orbital, but at the second the 1s orbital, but at the second level, as well as a 2s orbital, there level, as well as a 2s orbital, there are also orbitals called are also orbitals called 2p orbitals.2p orbitals.

A p orbital is rather like A p orbital is rather like 2 identical balloons tied 2 identical balloons tied together at the nucleus. together at the nucleus. The diagram on the The diagram on the right is a cross-section right is a cross-section through that 3-through that 3-dimensional region of dimensional region of space. Once again, the space. Once again, the orbital shows where orbital shows where there is a 95% chance there is a 95% chance of finding a particular of finding a particular electron. electron. At any one At any one energy level it is energy level it is possible to have possible to have three absolutely three absolutely equivalent p orbitalsequivalent p orbitals

d and f orbitalsd and f orbitals In addition to s and p orbitals, there In addition to s and p orbitals, there

are two other sets of orbitals which are two other sets of orbitals which become available for electrons to become available for electrons to inhabit at higher energy levels. At inhabit at higher energy levels. At the third level, there is a set of the third level, there is a set of five five d orbitalsd orbitals (with complicated shapes (with complicated shapes and names) as well as the 3s and 3p and names) as well as the 3s and 3p orbitals . At the third level there are orbitals . At the third level there are a total of nine orbitals altogether a total of nine orbitals altogether

d and f orbitalsd and f orbitals At the fourth level, as well the 4s and At the fourth level, as well the 4s and

4p and 4d orbitals there are an 4p and 4d orbitals there are an additional additional seven f orbitalsseven f orbitals - 16 - 16 orbitals in all. s, p, d and f orbitals orbitals in all. s, p, d and f orbitals are then available at all higher are then available at all higher energy levels as wellenergy levels as well

d and f orbitalsd and f orbitals You have to be aware that there are You have to be aware that there are

sets of five d orbitals at levels from sets of five d orbitals at levels from the third level upwards, but you will the third level upwards, but you will not be expected name them. Apart not be expected name them. Apart from a passing reference, you won't from a passing reference, you won't come across f orbitals at all. come across f orbitals at all.

Fitting electrons into orbitalsFitting electrons into orbitals You can think of an atom as a very You can think of an atom as a very

bizarre house (like an inverted bizarre house (like an inverted pyramid!) - with the nucleus living on pyramid!) - with the nucleus living on the ground floor, and then various the ground floor, and then various rooms (orbitals) on the higher floors rooms (orbitals) on the higher floors occupied by the electrons. occupied by the electrons.

Fitting electrons into orbitalsFitting electrons into orbitals On the first floor there is only 1 room On the first floor there is only 1 room

(the 1s orbital); on the second floor (the 1s orbital); on the second floor there are 4 rooms (the 2s, and three there are 4 rooms (the 2s, and three 2p orbitals); on the third floor there 2p orbitals); on the third floor there are 9 rooms (one 3s orbital, three 3p are 9 rooms (one 3s orbital, three 3p orbitals and five 3d orbitals); and so orbitals and five 3d orbitals); and so on. But the rooms aren't very big . . . on. But the rooms aren't very big . . . Each orbital can only hold 2 Each orbital can only hold 2 electrons.electrons.

Fitting electrons into orbitalsFitting electrons into orbitals A convenient way of showing the A convenient way of showing the

orbitals that the electrons live in is to orbitals that the electrons live in is to draw "electrons-in-boxes".draw "electrons-in-boxes".

"Electrons-in-boxes""Electrons-in-boxes" Orbitals can be represented as boxes Orbitals can be represented as boxes

with the electrons in them shown as with the electrons in them shown as arrows. Often an up-arrow and a arrows. Often an up-arrow and a down-arrow are used to show that down-arrow are used to show that the electrons are in some way the electrons are in some way different.different.

"Electrons-in-boxes""Electrons-in-boxes" A 1s orbital holding A 1s orbital holding

2 electrons would 2 electrons would be drawn as shown be drawn as shown on the right, but it on the right, but it can be written can be written even more quickly even more quickly as 1sas 1s22. This is read . This is read as "one s two" - not as "one s two" - not as "one s squared".as "one s squared".

"Electrons-in-boxes""Electrons-in-boxes" You mustn't You mustn't

confuse the two confuse the two numbers in this numbers in this notation:notation:

The order of filling orbitalsThe order of filling orbitals Electrons fill low energy orbitals Electrons fill low energy orbitals

(closer to the nucleus) before they fill (closer to the nucleus) before they fill higher energy ones. Where there is a higher energy ones. Where there is a choice between orbitals of equal choice between orbitals of equal energy, they fill the orbitals singly as energy, they fill the orbitals singly as far as possible.far as possible.

The order of filling orbitalsThe order of filling orbitals The diagram (not The diagram (not

to scale) to scale) summarizes the summarizes the energies of the energies of the orbitals up to the orbitals up to the 4p level.4p level.

s- and p-block elementss- and p-block elements The elements in group 1 of the The elements in group 1 of the

Periodic Table all have an outer Periodic Table all have an outer electronic structure of nselectronic structure of ns11 (where n is (where n is a number between 2 and 7). All a number between 2 and 7). All group 2 elements have an outer group 2 elements have an outer electronic structure of nselectronic structure of ns22. Elements . Elements in groups 1 and 2 are described as s-in groups 1 and 2 are described as s-block elements.block elements.

s- and p-block elementss- and p-block elements Elements from group 3 across to the Elements from group 3 across to the

noble gases all have their outer noble gases all have their outer electrons in p orbitals. These are electrons in p orbitals. These are then described as p-block elements.then described as p-block elements.

s- and p-block elementss- and p-block elements

d-block elementsd-block elements d-block elements are elements in d-block elements are elements in

which the last electron to be added to which the last electron to be added to the atom is in a d orbital. the atom is in a d orbital.

Remember that the 4s orbital has a Remember that the 4s orbital has a lower energy than the 3d orbitals and lower energy than the 3d orbitals and so fills first. Once the 3d orbitals have so fills first. Once the 3d orbitals have filled up, the next electrons go into filled up, the next electrons go into the 4p orbitals as you would expect. the 4p orbitals as you would expect.

d-block elementsd-block elements

QUARKSQUARKS Up until 1964, it was believed that there Up until 1964, it was believed that there

only existed three elementary particles only existed three elementary particles making up the atom: the electron, the making up the atom: the electron, the proton and the neutron. proton and the neutron. However, However, numerous unstable particles (with a numerous unstable particles (with a lifetime of the order of 10-23 lifetime of the order of 10-23 seconds) have been detectedseconds) have been detected, either , either in cosmic rays, or in the high-energy in cosmic rays, or in the high-energy impacts created in impacts created in particle particle acceleratorsaccelerators constructed after the constructed after the 1939-1945 war. 1939-1945 war.

QUARKSQUARKS Set out for the first time in 1964 by Set out for the first time in 1964 by Murray Murray

Gell-MannGell-Mann and independently by George and independently by George Zweig, Zweig, the theory of quarksthe theory of quarks progressively progressively established its pedigree and won acclaim as established its pedigree and won acclaim as advances corroborated the theory by advances corroborated the theory by experiment; it was not until 1975 that experiment; it was not until 1975 that quarks were detected experimentally. quarks were detected experimentally.

The strange name of Quark comes from a The strange name of Quark comes from a Roman phrase of James Joyce in "Finnegan’s Roman phrase of James Joyce in "Finnegan’s Wake": Wake": Three Quarks for Muster Mark!Three Quarks for Muster Mark!

QUARKSQUARKS Quarks have a unique property: they Quarks have a unique property: they

are incapable of existing alone, are incapable of existing alone, unaccompaniedunaccompanied! It is absolutely ! It is absolutely impossible to observe a quark in impossible to observe a quark in isolation.isolation.

Quarks are the constituents of nucleons. Quarks are the constituents of nucleons. There exist two types in ordinary matter :There exist two types in ordinary matter : up quark (symbol = u) up quark (symbol = u) down quark (symbol = d) down quark (symbol = d)

AntimatterAntimatter There exists a mirror universe where There exists a mirror universe where

matter is transformed into matter is transformed into anti-anti-mattermatter..

Antimatter is composed of Antimatter is composed of antiparticlesantiparticles: antiquarks, anti-: antiquarks, anti-electrons, and antineutrinos.electrons, and antineutrinos.

An antiparticle is simply a particle An antiparticle is simply a particle with opposing quantum numberswith opposing quantum numbers

How many atoms are there?How many atoms are there? In nature, about 90 different In nature, about 90 different

atoms existatoms exist which combine to form which combine to form an infinite variety of compounds. It is an infinite variety of compounds. It is necessary to add to this natural necessary to add to this natural radioactive atoms (and therefore radioactive atoms (and therefore unstable) and those created unstable) and those created artificially by man by nuclear artificially by man by nuclear reactions. reactions.

How many atoms are there?How many atoms are there? At the moment, about At the moment, about 115 atoms115 atoms exist which exist which

have been discovered or created, but the list have been discovered or created, but the list could grow. The last atom created is element could grow. The last atom created is element 114, baptized with a provisional name of 114, baptized with a provisional name of ununquadium (symbol Uuq): It was created in ununquadium (symbol Uuq): It was created in 1998 at the Nuclear Institute of Dubna in 1998 at the Nuclear Institute of Dubna in Russia. Russia.

Late breaking news: Late breaking news: Elements 116Elements 116 and and 118118 have been synthesized in 1999 in have been synthesized in 1999 in California at the California at the Lawrence Berkeley National LaboratoryLawrence Berkeley National Laboratory

http://enews.lbl.gov/Science-Articles/Archive/elements-116-118.html

The 3 radiationsThe 3 radiations There exist three varieties of There exist three varieties of

radioactivity characterized by the radioactivity characterized by the emission of different rays emitted by emission of different rays emitted by the nucleus of the atom: the nucleus of the atom:

The 3 radiationsThe 3 radiations αα (alpha) rays (alpha) rays are stopped by 6 cm of are stopped by 6 cm of

air. They are composed of alpha particles air. They are composed of alpha particles made up of two protons and two neutrons made up of two protons and two neutrons (in fact a helium nucleus). The particle is (in fact a helium nucleus). The particle is therefore positively charged. These alpha therefore positively charged. These alpha particles are nothing more than particles are nothing more than fragments of unstable heavy nuclei that fragments of unstable heavy nuclei that reorganize themselves to become lighter reorganize themselves to become lighter and more stable nuclei (thus non and more stable nuclei (thus non radioactive!). radioactive!).

The 3 radiationsThe 3 radiations ββ (beta) (beta) rays rays are stopped by an are stopped by an

aluminum screen. They are notably aluminum screen. They are notably composed of electrons and are composed of electrons and are therefore negatively charged. Beta therefore negatively charged. Beta radiation is identical to the cathode radiation is identical to the cathode radiation in your TV! radiation in your TV!

The 3 radiationsThe 3 radiations γγ (gamma) (gamma) rays rays are extremely are extremely

penetrating and can pass straight penetrating and can pass straight through a safe. They are composed through a safe. They are composed of high-energy photons (particles of of high-energy photons (particles of light). They are nothing but pure light). They are nothing but pure energy without any mass. energy without any mass.

The 3 radiationsThe 3 radiations These three varieties of radioactivity These three varieties of radioactivity

are not emitted simultaneously. are not emitted simultaneously. Each Each nuclear reaction of an atom emits nuclear reaction of an atom emits only one single type of radiation only one single type of radiation at a time!at a time! For exampleFor example, radioactive , radioactive Uranium-238Uranium-238 emits an alpha ray and emits an alpha ray and thus loses 4 nucleons (2 protons + 2 thus loses 4 nucleons (2 protons + 2 neutrons): U 238 thereby transforms neutrons): U 238 thereby transforms itself into itself into Thorium-234Thorium-234 (because 2 (because 2 protons less - that changes an atom!). protons less - that changes an atom!).

Nuclear fissionNuclear fission Whenever the nucleus of a heavy atom (like Whenever the nucleus of a heavy atom (like

uranium 235uranium 235) fissions (fragments) into two ) fissions (fragments) into two smaller nuclei, it produces a remarkable smaller nuclei, it produces a remarkable event: the sum of the masses of these two event: the sum of the masses of these two remaining nuclei is less than the mass of remaining nuclei is less than the mass of the original large nucleus. the original large nucleus. Where has the Where has the missing mass gone? It has transformed missing mass gone? It has transformed itself into pure energy (Einstein's itself into pure energy (Einstein's mass-energy equivalence), an mass-energy equivalence), an enormous quantity of energy.enormous quantity of energy.

Nuclear fusionNuclear fusion In broad terms it's the inverse of fission. In broad terms it's the inverse of fission. Two light atomic nuclei (like hydrogen) Two light atomic nuclei (like hydrogen)

crash into each other and fuse together crash into each other and fuse together into a single bigger nucleus. Now the final into a single bigger nucleus. Now the final mass of this big nucleus is smaller than mass of this big nucleus is smaller than the sum of the masses of the two initial the sum of the masses of the two initial nuclei, which is where we get an nuclei, which is where we get an enormous release of energy produced by enormous release of energy produced by the annihilation of this difference of mass. the annihilation of this difference of mass.

Nuclear fusionNuclear fusion In order to be able to provoke such a fusion In order to be able to provoke such a fusion

reaction, it is necessary to force the nuclei, reaction, it is necessary to force the nuclei, all positively charged, to move together and all positively charged, to move together and to overcome their mutual repulsion : This is to overcome their mutual repulsion : This is not possible except at very high not possible except at very high temperatures (the temperature temperatures (the temperature corresponding to the intensity necessary to corresponding to the intensity necessary to get the particles to crash into each other). get the particles to crash into each other). This is why the nuclear fusion reaction is also This is why the nuclear fusion reaction is also called a called a thermonuclear reaction thermonuclear reaction (thermo = (thermo = heat). heat).

Nuclear fusionNuclear fusion This uncontrolled reaction is used in This uncontrolled reaction is used in

the hydrogen bomb or the hydrogen bomb or H-bombH-bomb. This . This reaction is also seen in the heart of reaction is also seen in the heart of our our SunSun where temperatures reach where temperatures reach hundreds of millions of degrees. hundreds of millions of degrees.

Natural or artificial radioactivity?Natural or artificial radioactivity?

Man has not invented radioactivity. It Man has not invented radioactivity. It has existed since the beginning of has existed since the beginning of the universe: We speak of the universe: We speak of natural natural radioactivityradioactivity when it is due to the when it is due to the durable radio-elements formed in the durable radio-elements formed in the stars which have not yet found their stars which have not yet found their stable state: they will end up stable state: they will end up transforming themselves into stable transforming themselves into stable atoms. atoms.

Natural or artificial radioactivity?Natural or artificial radioactivity? We speak of We speak of artificial radioactivity artificial radioactivity when when

referring to referring to elements fabricated by manelements fabricated by man. . In this case, these atoms are very heavy In this case, these atoms are very heavy (with a high atomic number Z), very (with a high atomic number Z), very unstable and therefore have a very short unstable and therefore have a very short half-life. Physicists create these artificial half-life. Physicists create these artificial radioelements by bombarding natural atoms radioelements by bombarding natural atoms with protons or alpha particles: the nuclei of with protons or alpha particles: the nuclei of these atoms acquire additional protons that these atoms acquire additional protons that transform them into new heavier atoms. transform them into new heavier atoms.

Documents

ATOMS Ancient Greece to Now. DEFINED Atom (n.)- A unit of matter, the smallest unit of an element, consisting of a dense, central, positively charged