Atoms, Elements and the Periodic TableAtoms, Elements and the Periodic Table28 September 200628 September 2006

PhysicsPhysics

ChemistryChemistryAstronomyAstronomy

GeologyGeologyBiologyBiology

TopicsTopics

Discovery of atomic structure and functionDiscovery of atomic structure and functionModels of atomsModels of atoms

Bohr atom (1913)Bohr atom (1913)Quantum mechanics (1930’s)Quantum mechanics (1930’s)

Elements and atomsElements and atomsElectrons and orbits/shells Electrons and orbits/shells Valence electronsValence electrons

Scientific MethodScientific Method

Observations

Hypothesis

Test of Hypothesis

Reject/Accept

Models in the SciencesModels in the Sciences

Example: Dynamics of family Example: Dynamics of family interactionsinteractions

Example for atoms: Example for atoms: 1. Atom as a marble1. Atom as a marble2. Atom as the solar system2. Atom as the solar system3. Atom with protons, 3. Atom with protons, neutrons and electronsneutrons and electrons

Models: abstraction and meant Models: abstraction and meant to be challengedto be challenged

Protons and Neutron

Electrons in orbits

Crystal Morphology and Color: Crystal Morphology and Color: Atomic StructureAtomic Structure

Leaf Color and Atomic StructureLeaf Color and Atomic Structure

Compounds to Subatomic Particles:Compounds to Subatomic Particles:A HierarchyA Hierarchy

CompoundCompound

ElementElement

AtomAtom

Subatomic ParticlesSubatomic Particles

Emergent Properties?

Thompson’s Investigation of the Thompson’s Investigation of the ElectronElectron

Idea that smaller components comprise atomsIdea that smaller components comprise atomsHypothesisHypothesis: Atoms consist of subcomponents, : Atoms consist of subcomponents, one of which is negatively charged with a very one of which is negatively charged with a very small masssmall massTesting the hypothesisTesting the hypothesis

Thompson’s ExperimentThompson’s Experiment

Observations:1. Deflection of negatively-

charged beam

2. Very small mass relative to

charge

3. Mass same for all elements

tested

Hypothesis: Accept

Particle name: Electron

Methodology

Rutherford’s Investigation of the Rutherford’s Investigation of the NucleusNucleus

Idea that other smaller components are part of Idea that other smaller components are part of atoms, including ones that are positively chargedatoms, including ones that are positively chargedHypothesisHypothesis: Atoms consist of multiple : Atoms consist of multiple subcomponents, some of which are positivesubcomponents, some of which are positiveTesting the hypothesisTesting the hypothesis

Alpha particles (+), gold foil, “bullets”, and “tracks”Alpha particles (+), gold foil, “bullets”, and “tracks”

Rutherford’s Experiment: Rutherford’s Experiment: MethodologyMethodology

Observations, Hypothesis and Observations, Hypothesis and ConclusionConclusion

ObservationsObservationsAlmost all alpha’s (+) passed through foil unaffectedAlmost all alpha’s (+) passed through foil unaffectedVery small number of alpha’s (+) deflected at a small angleVery small number of alpha’s (+) deflected at a small angle1/1000 bounced back1/1000 bounced back

HypothesisHypothesis: Atom consists of a positive : Atom consists of a positive subcomponent that is small in volume in comparison subcomponent that is small in volume in comparison to atom itselfto atom itselfAccept/reject?Accept/reject?Conclusions: Conclusions:

radius of nucleus is 10radius of nucleus is 10--44 x radius of atomx radius of atomName of particle is the protonName of particle is the proton

Atomic Structure: Bohr AtomAtomic Structure: Bohr Atom

Observations (1913)Observations (1913)Heat hydrogen gas and light emitted as a Heat hydrogen gas and light emitted as a discretediscretewavelengths (not continuous spectrum)wavelengths (not continuous spectrum)Other gases behave the same in producing discrete Other gases behave the same in producing discrete wavelength, but each gas is unique in wavelengths wavelength, but each gas is unique in wavelengths emitted (e.g., violet versus yellow versus red)emitted (e.g., violet versus yellow versus red)

Hypothesis and ModelHypothesis and Model

Quantum Concepts:

1. Only allowed orbits for

electrons

2. Discrete frequency of

photon (emitted light)

Model: Quantum MechanicsModel: Quantum Mechanics

Theory of Quantum MechanicsTheory of Quantum Mechanics

ObservationsObservationsBehavior of electrons in heated hydrogen gas consistent with Behavior of electrons in heated hydrogen gas consistent with Bohr Model (orbits, etc.)Bohr Model (orbits, etc.)Behavior of other heavier gases not explained by Bohr ModelBehavior of other heavier gases not explained by Bohr Model

Investigators (Heisenberg, Shrodinger): waveInvestigators (Heisenberg, Shrodinger): wave--particle particle duality of light (remember Dr. Geller’s lecture)duality of light (remember Dr. Geller’s lecture)Key: integrated mechanisms of waves and particles, Key: integrated mechanisms of waves and particles, focusing on “fuzzy electron clouds”/focusing on “fuzzy electron clouds”/waveswavesHypothesisHypothesis: new model of atomic structure and : new model of atomic structure and function: quantum mechanics function: quantum mechanics theorytheory of the atomof the atom

Incorporation of known facts (Bohr model as particles)Incorporation of known facts (Bohr model as particles)Wave properties of electrons in orbitsWave properties of electrons in orbitsPrediction of new properties yet to be discoveredPrediction of new properties yet to be discovered

QuestionsQuestions

Is a model in the sciences a form of an Is a model in the sciences a form of an hypothesis?hypothesis?

All of these models (when accepted or rejected) All of these models (when accepted or rejected) resulted in scientific revolutions in physics. resulted in scientific revolutions in physics. Revolutions in the sciences are somewhat Revolutions in the sciences are somewhat analogous to revolutions in society?analogous to revolutions in society?

According to the Rutherford model of the atom, the volume of any atom is largely _______.

A. protons and neutronsB. electronsC. empty spaceD. noxiously sequenced nuons surrounded by

pompous protonsE. none of the above

QuestionQuestion

The existence of a tiny, massive, and positively charged atomic nucleus was deduced from the observation that ___.

A. fast, massive, and positively charged alpha particles move in straight lines through gold foil

B. alpha particles were deflected by a magnetic fieldC. some alpha particles were deflected by metal foilD. all of the above

QuestionQuestion

According to the Bohr model of the atom, an electron gains or looses energy only by ______.

A. jumping from one atom to anotherB. speeding up or slowing down in its

orbitC. jumping from one orbit to anotherD. being removed from the atom

QuestionQuestion

TopicsTopics

Discovery of atom structure and functionDiscovery of atom structure and functionModels of atomsModels of atoms

Bohr atom (1913)Bohr atom (1913)Quantum mechanics (1930’s)Quantum mechanics (1930’s)

Elements and atomsElements and atomsElectrons and orbits nested within shells Electrons and orbits nested within shells Valence electronsValence electrons

ElementsElements

PatternsPatterns92 naturally occurring elements (e.g., hydrogen, gold, helium)92 naturally occurring elements (e.g., hydrogen, gold, helium)Total of 113Total of 11325 of 92 are essential to life (e.g., what are they?)25 of 92 are essential to life (e.g., what are they?)

Key pointsKey pointsany element is the same in its chemical structure and physical any element is the same in its chemical structure and physical properties (stable over time, with one exception properties (stable over time, with one exception -- radioactive radioactive elements)elements)All elements have origin in either the big bang (hydrogen and All elements have origin in either the big bang (hydrogen and helium) or the subsequent evolution of the universe (Dr. helium) or the subsequent evolution of the universe (Dr. Geller will speak to this a bit later)Geller will speak to this a bit later)

At No Symbol Name

1 H Hydrogen2 He Helium

6 C Carbon7 N Nitrogen8 O Oxygen

17 Cl Chlorine18 Ar Argon

26 Fe Iron27 Co Cobalt

53 I Iodine

73 Ta Tantalum74 W Tungsten

79 Au Gold80 Hg Mercury

94 Pu Plutonium

104 Rf Rutherfordium

Elements and CompoundsElements and Compounds

CompoundCompoundElements combine in very precise ways that are recurrent and Elements combine in very precise ways that are recurrent and predictablepredictableSodium + Chlorine = Sodium ChlorideSodium + Chlorine = Sodium ChlorideNaNa + Cl =+ Cl = NaClNaCl

metal + gas = solidmetal + gas = solidKey points Key points

Atoms of sodium (Na) and chlorine (Cl) remain atoms of Atoms of sodium (Na) and chlorine (Cl) remain atoms of eacheachProduct (NaCl) is recurrent and predictableProduct (NaCl) is recurrent and predictableEmergentEmergent propertyproperty: “emergence” of new properties in a : “emergence” of new properties in a compound not be explained by the summation of the two compound not be explained by the summation of the two elements (elements (hierarchy theoryhierarchy theory))Other example: Hydrogen + oxygen = __________Other example: Hydrogen + oxygen = __________

Compounds to Subatomic Particles:Compounds to Subatomic Particles:A HierarchyA Hierarchy

CompoundCompound

ElementElement

AtomAtom

Subatomic ParticleSubatomic Particle

Emergent Properties

Subatomic ParticlesSubatomic Particles

Atoms are composed of subatomic particlesAtoms are composed of subatomic particlesMost stable particlesMost stable particles

NeutronsNeutronsProtonsProtonsElectronsElectrons

Other less stable particles (quarks, neutrinos, etc.)Other less stable particles (quarks, neutrinos, etc.)Relationship among the more stable particlesRelationship among the more stable particles

NeutronNeutron ProtonProton ElectronElectronChargeCharge neutralneutral positivepositive negativenegativeMassMass 2x102x10--2424 g g 2x102x10--2424 g g 5x105x10--2828 gg

Model of Atomic Structure: ParticlesModel of Atomic Structure: Particles

Protons and Neutron

Electrons in orbits

Atomic StructureAtomic Structure

Atoms of the same element have the same number of Atoms of the same element have the same number of subatomic particles, abbreviated as follows:subatomic particles, abbreviated as follows:

22 # of protons# of protons

HeliumHelium HeHe Abbreviation of elementAbbreviation of element44 Atomic mass (g/mole)Atomic mass (g/mole)

11

HydrogenHydrogen HH11

Mass = Mass = Protons + NeutronsProtons + Neutrons

ElectronsElectrons

Background of quantum mechanicsBackground of quantum mechanicsEnergy “Energy “baronsbarons” of the atom (motion) ” of the atom (motion)

Energy = ability to do workEnergy = ability to do workPotential energy = energy stored due to Potential energy = energy stored due to position or location (analogy to water in a position or location (analogy to water in a tower)tower)

Charge is negative (Charge is negative (--) and particle is ) and particle is alwaysalways in in motionmotionCapturing an atom and its orbiting electron may Capturing an atom and its orbiting electron may be difficult (why?)be difficult (why?)

Key to Electron StructureKey to Electron Structure

Count the number of protons as the number of Count the number of protons as the number of electrons = number of protonselectrons = number of protonsElectrons are negative in charge and in Electrons are negative in charge and in constant motion (as a wave)constant motion (as a wave)Electrons are in orbits around the nucleus and Electrons are in orbits around the nucleus and orbits are nested within shellsorbits are nested within shells

ElectronsElectrons

Example of Sulfur (Example of Sulfur (16163232S)S)

(16 electrons in 3 shells)(16 electrons in 3 shells)

What are shells and what are orbits?

Quantum Mechanics and OrbitsQuantum Mechanics and Orbits

Example of Electrons in ShellsExample of Electrons in Shells

As electrons move among shells, they change As electrons move among shells, they change potential energypotential energy

Hot summer day, bright sun and car topHot summer day, bright sun and car topLight absorption by pigments and electrons “jump” to Light absorption by pigments and electrons “jump” to higher shell (potential energy); give off energy when they higher shell (potential energy); give off energy when they drop back (kinetic energy)drop back (kinetic energy)

Banana, orange juice or bagel this AM?Banana, orange juice or bagel this AM?Excited electron “captured” by chlorophyll in leaf and Excited electron “captured” by chlorophyll in leaf and shuttled to a sugar molecule in its excited state (potential shuttled to a sugar molecule in its excited state (potential energy) until you release the energy energy) until you release the energy viavia digestion, allowing digestion, allowing the electron to “drop back” to a lower orbit (kinetic energy)the electron to “drop back” to a lower orbit (kinetic energy)

Some Keys to Electron StructureSome Keys to Electron Structure

Electrons reside in shells as a function of Electrons reside in shells as a function of quantum mechanics (1quantum mechanics (1--4 orbits per shell)4 orbits per shell)Never more than two electrons per orbit (Pauli’s Never more than two electrons per orbit (Pauli’s Exclusion Principle)Exclusion Principle)Distribution of electrons is key to understanding Distribution of electrons is key to understanding why elements and atoms behave the way they dowhy elements and atoms behave the way they doOutermost electrons are called Outermost electrons are called valence electrons; valence electrons; they have special significance in chemistrythey have special significance in chemistry

Periodic Table of ElementsPeriodic Table of Elements

Concept: most stable state for an atom is one in Concept: most stable state for an atom is one in which the outermost shell is filled with the which the outermost shell is filled with the maximum number of electronsmaximum number of electrons11stst Shell (1 orbit; 2 electrons)Shell (1 orbit; 2 electrons)

Hydrogen (Hydrogen (1111H; 1 electron; stable ?)H; 1 electron; stable ?)

Helium (Helium (2244He; 2 electrons; stable ?)He; 2 electrons; stable ?)

Periodic Table’s 1Periodic Table’s 1stst RowRowHydrogen and HeliumHydrogen and Helium

Periodic Table of ElementsPeriodic Table of Elements

22ndnd shell has 4 orbits with 2 electrons shell has 4 orbits with 2 electrons (maximum) per orbit (total of 8 electrons/shell)(maximum) per orbit (total of 8 electrons/shell)Most stable configuration is:Most stable configuration is:

11stst shell filled with 2 electronsshell filled with 2 electrons22ndnd shell filled with 8 electronsshell filled with 8 electronsTotal of 10 electrons (Total of 10 electrons (1010

2020Ne)Ne)

22ndnd row of Periodic Tablerow of Periodic Table8 elements8 elements

Periodic Table of ElementsPeriodic Table of Elements

33ndnd shell has 4 orbits with 2 electrons maximum shell has 4 orbits with 2 electrons maximum per orbit (total of 8 electrons/shell)per orbit (total of 8 electrons/shell)Most stable configuration is the following:Most stable configuration is the following:

11stst shell filled with 2 electronsshell filled with 2 electrons22ndnd shell filled with 8 electronsshell filled with 8 electrons33rdrd shell filled with 8 electronsshell filled with 8 electronsTotal of ___ electrons (Total of ___ electrons (1818

4040Ar)Ar)33ndnd row of Periodic Tablerow of Periodic Table

8 elements (list and relate to the above)8 elements (list and relate to the above)

Periodic Table of ElementsPeriodic Table of Elements

Number of elements in a row is not chance but Number of elements in a row is not chance but reflects the maximum number of electrons in reflects the maximum number of electrons in the outermost shellthe outermost shell

Row 1 = 2Row 1 = 2Row 2 = 8Row 2 = 8Row 3 = 8Row 3 = 8Row 4 = 18Row 4 = 18etcetc

Predictive Value of Periodic TablePredictive Value of Periodic Table

Discussion QuestionDiscussion Question

As you scan the night sky, you see multiple objects and As you scan the night sky, you see multiple objects and question whether these objects are similar to or question whether these objects are similar to or different from the Earth in chemical composition (i.e., different from the Earth in chemical composition (i.e., elements).elements).

Suppose the person next to you says that she has an Suppose the person next to you says that she has an instrument that can identify the occurrence of specific instrument that can identify the occurrence of specific atoms (e.g., sodium, hydrogen, sulfur) based on the atoms (e.g., sodium, hydrogen, sulfur) based on the energy patterns/signatures of electrons in atoms on energy patterns/signatures of electrons in atoms on that planet. Could she be right? that planet. Could she be right?

In the list below, an atom of _______ has the greatest ability to attract electrons.

A. siliconB. sulfurC. kryptonD. chlorineE. sodium

QuestionQuestion

In the list below, an atom of _______ has the least ability to attract electrons.

A. siliconB. sulfurC. kryptonD. chlorineE. sodium

QuestionQuestion

Discussion QuestionDiscussion Question

Models are one of the key investigative tools in Models are one of the key investigative tools in the scientific arsenal. Models of our the scientific arsenal. Models of our understanding of the atom are a classic example understanding of the atom are a classic example of the role that models play in the sciences.of the role that models play in the sciences.

List four features of models List four features of models –– not the specifics not the specifics of any given model, but rather how models are of any given model, but rather how models are constructed, how they promote our constructed, how they promote our understanding of natural systems, and how their understanding of natural systems, and how their fallibility is an asset.fallibility is an asset.

Discussion QuestionDiscussion Question

In many ways, the Periodic Table is a “model” In many ways, the Periodic Table is a “model” to help scientists understand patterns in the to help scientists understand patterns in the natural world. List ways in which this model natural world. List ways in which this model helps scientists to understand the natural world?helps scientists to understand the natural world?

How does this model compare with that of How does this model compare with that of Rutherford’s model or the quantum mechanics Rutherford’s model or the quantum mechanics model of the atom?model of the atom?