Upload
others
View
4
Download
0
Embed Size (px)
Citation preview
1
History of Atomic Theory
Alchemy ~ Before 400 B.C.
Experiment:
Beliefs:
Pseudoscience concerned with:
• Changing metal to gold• Finding an eternal life elixir
• All matter was made up of a combination of the four elements• Four elements: fire, wind, earth, water
Aristotle
2
Experiment: None. He had beliefs that were disregarded.
Beliefs:
Democritus ~ 400 B.C.
History of Atomic Theory
• Named the atom "Atomos." It means indivisible• Matter is composed of atoms too small to be seen.• Empty space between atoms• Atoms are solid and homogeneous• Different atoms have different sizes and shapes
Model: Sphere
Democritus
3
Sphere-Billiard balls
Experiment:
Beliefs:
History of Atomic Theory
Dalton ~ early 1803 English School Teacher
Studied chemical reactions, making observations and measurements
Five Principles-Dalton's Atomic Theory
1. All matter is made of indestructible atoms.
2. Atoms of the same element are identical in their physical and chemical properties.
3. Atoms of different elements have different physical and chemical properties.
4. Atoms of different elements combine in simple whole number ratios to form chemical compounds.
5. In chemical reactions, atoms cannot be subdivided, created, or destroyed. They are combined, separated, or rearranged.
Model: Which principles remain true today?
John Dalton
4
Experiment:
Discoveries:
Model:
J.J. Thomson ~ 1897 English Physicist
History of Atomic Theory
Cathode Ray TubeElectricity is passed through a gas tube. The gas beam can be bent with a magnet.
• Atoms consist of charged particles• The negatively charged particles are called electrons (1897)• The positively charged particles are called protons (1920)
Plum Pudding or Chocolate Chip CookiesThe chocolate chips are electrons stuck in positive dough
Joseph John Thomson
5
History of Atomic Theory
Experiment:
Model:
Discoveries:
Rutherford ~ 1911 English Physicist (a student of Thomson)
Gold Foil Experiment
Positively charged alpha particles are shot at a piece of thin gold foil. Most alpha particles had little deflection. Some were deflected at large angles.
• A positively charged core of an atom called the nucleus• Electrons surround the nucleus• The rest of the atom is empty space
Nuclear atom
Quote: "It was about as believable as if you had fired a 15 inch shell at a piece of tissue paper, and it came back and hit you."- Rutherford
Ernest Rutherford
6
History of Atomic Theory
Experiment:
Discoveries:
Model:
James Chadwick ~ 1932 English Physicist (Student of Rutherford)
• A neutrally charged subatomic particle• The particle was called a neutron
Sir James Chadwick• Beryllium foil was bombarded with alpha particles• A neutral radiation was emitted• Emitted radiation would then knock protons out of the nuclei of other substances• The radiation was a stream of neutral particles having the same mass as a proton
Same as Rutherford
7
http://glencoe.mcgrawhill.com/sites/dl/free/0078759864/164155/00044672.html
Review History of Atom
8
History of Atomic Theory
Experiment:
Discoveries:
Model:
Bohr ~ 1913 Danish Physicist (a student of Rutherford)
Problem: According to the laws of physics, charged particles will radiate energy when orbiting and spiral into the nucleus. Rutherford's atoms would all collapse.
Niels Bohr
Light SpectrumsElectrons give off energy in the form of colored light by falling from an excited state to a ground state.
Photo courtesy NASA
Hydrogen Spectrum
Helium Spectrum
• Electrons can only be found at certain energy levels• Each energy level requires a certain amount of energy• Lower (closer) levels have lower energy• Higher (farther) levels have higher energy
Vocabulary:ground state- all electrons in their lowest possible energy levelsexcited state-electrons absorbed energy & jump to a higher energy level
Ladder Rungs-Cannot stand in between rungs
9
10
11
History of Atomic Theory
Experiment:
Discoveries:
Model:
Quantum Mechanics
Erwin Schrodinger ~ 1926 Austrian Physicist
NONE! It is a mathematical model. It cannot be represented by anything that exists in the real world.
Erwin Schrodinger
Mathematical Equation:
• Mathematical model that deals with the probability of finding an electron within a given space• The probability is 90%• The given space are called orbitals (or electron clouds)• There are four orbitals with different shapes s p d f• These orbitals can be related to the periodic table• Electrons have wave properties
Problem: Bohr's model works well for Hydrogen, but fails for every other element
12
Electromagnetic Radiation: waves that are produced by electrically charged particles
Ex: sunlight, X rays, microwaves
Electromagnetic Spectrum
13
14
All electromagnetic radiation exhibits wave like behavior (wavelength, frequency, and speed)
15
Quantum Numbers: Specify the properties of atomic orbitals and the properties of electrons in those orbitals. Each e- has a set of four numbers; no two electrons in the same atom can have the same four numbers.
Four Quantum Numbers: Principal Angular Magnetic Spin
1. Principal Quantum Number (n)-
2. Angular Quantum Number (l)-
Refers to the distance of the orbital from the nucleus (says which of the main energy levels an e- is in)
• When n=1 is closest to the nucleus and has the least energy• n=1,2,3,4,5, etc.
Refers to the shape of the orbital (also associated with angular momentum)
a. Possible Shapes• s, p, d, f (in order of increasing energy)• l=integer values from 0 to n-1
b. Number of possible shapes is limited by the principal quantum number
16
3. Magnetic Quantum Number (m)-
4. Spin Quantum Number (s)-
Orientation of orbital(s) (direction of angular momentum)
- m=any integer from -l to +l
State of the electron that occupies an orbital
-Electrons are assigned one of the two possible directions it can be spinning
- + spin or - spin
17
18
19
20
21
Heisenberg's Uncertainty Principle: you can never know how fast an electron is moving and where an electron is at the same time. In other words, you can find out where the electron started and you can see where the electron ended up but how it got there WE DON'T KNOW!
22
Electron Configuration: The arrangement of electrons in an atom is known as the atoms electron configuration.
Rules:
1. Aufbau Principle: An electron occupies the lowest energy level that can receive it.
2. Pauli Exculsion Principle: No two electrons in the same atom can have the same set of four quantum numbers.
• If two electrons have the same n, m, and l values they have to have different spins• Two electrons fit into each orbital
3. Hund's Rule: Orbitals of equal energy are each occupied by one electron before any orbital is occupied by a second electron, and all electrons in singly occupied orbitals must have the same spin
23
24
25
4th energy level
3rd energy level
2nd energy level
1st energy level
1s
2s2p
3s
3p
4s
3d
4p
26
27
28
29
30
Attachments
Pictures of atom
Chadwick apparatus
Time line of scientists
Schrodinger equation
Conversation with science
orbitals