The Quiz Average (not including zeros): 57. How to improve 1)Review Quiz and mistakes in Quiz. 2)Notice correlation between Quiz & Study Guide 3)Do the

The QuizThe Quiz

Average (not including zeros): 57

How to improveHow to improve1) Review Quiz and mistakes in Quiz.2) Notice correlation between Quiz & Study Guide3) Do the homework

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Atomic Structure Atomic Structure & Chemistry& Chemistry

Anyone who is not shocked about quantum theory has not understood it.- Nils Bohr

Nils Bohr (1885-1962) was a Danish Physicist. His model for the hydrogen atom helped build quantum theory.

Astronomy Question:How do we know the composition of a planet, or extra-solar planet, or star, or galaxy if we’ve never been there

Where we left offWhere we left off

Wait!Wait!

1) An accelerating charged particle emits electromagnetic radiation.2) Electrons in a circular orbit about a nucleus are accelerating.3) Thus the electrons should emit electromagnetic waves.4) Electromagnetic radiation carries away energy (E=hv)

5) Electrons lose energy and should fall into the nucleus(in less than 1 second!)

Let’s excite the atomic Let’s excite the atomic electronselectrons

You’re a physicist in 1830, maybe working with John HerschelYou decide to try to figure out what happens to an atom when you give it energy. So…

Let’s excite the atomic Let’s excite the atomic electronselectrons

However, you know more than a physicist in 1830, because you know that critical result from Max Planck; that is that the energy of a light particle - a photon - is E=hv, where h=6.626x10-34 J s, is the Planck constant and v is the frequency of light. Also you know that v = c/ (because I told you this last class).

Max Planck 1901

A prism separates light A prism separates light into its wavelength into its wavelength

componentscomponentsHowever, you know more than a physicist in 1830, because you know that critical result from Max Planck; that is that the energy of a light particle - a photon - is E=hv, where h=6.626x10-34 J s, is the Planck constant and v is the frequency of light. Also you know that v = c/l (because I told you this last class).

So does a gratingSo does a grating





The Riddle of the Hydrogen The Riddle of the Hydrogen SpectrumSpectrum

A simple formula defines the wavelengths of the spectral lines of atomic hydrogen.

microns11

97.101

22 ⎟⎠

⎞⎜⎝

⎛ −=mn

Where is the wavelength of the emitted light and n and m are integers.

Pick any two integers n and m (n must be less than m), calculate the wavelength and hydrogen will have a spectral line at that wavelength. No spectral lines exist at wavelengths not given by this equation.

ExamplesExamplesmicrons11

97.101

22 ⎟⎠

⎞⎜⎝

⎛ −=mn

N = 2, m = 3: = [10.97 (1/4 - 1/9) ] -1 = 0.656 microns = 656 nm

N = 2, m = 4: = [10.97 (1/4 - 1/16) ] -1 = 0.486 microns = 486 nm

N = 2, m = 5: = [10.97 (1/4 - 1/25) ] -1 = 0.365 microns = 365 nm

NOTE: units of length

1 micron = 10-6 meters1 nm = 10-9 meters

Bohr’s Atomic StructureBohr’s Atomic StructureAn atom arranges its electrons into discrete orbits.

These orbits have discrete energy levels, specific to the element.

For hydrogen, the energy of level n is: En = -10.97 h c /(n2)

For level m: Em = -10.97 h c /(m2)

When an atom jumps between level m and level n, where level m has the highest energy the atom looses energy equal to Em - En. Since energy is conserved this energy is contained in the photon which is emitted with an energy equal to E = h c/.

En = -10.97 h c/n2

Em = -10.97 h c/m2

Atomic electrons are in discrete orbits.

These orbits have discrete energy levels, specific to the element.

For hydrogen, the energies of level n is:

For level m:

Bohr’s Atomic StructureBohr’s Atomic Structure

En = -10.97 h c/n2

Em = -10.97 h c/m2






En = -10.97 h c/n2

Em = -10.97 h c/m2

Total Energy :

Em = -10.97 h c /(m2)

When an atom jumps between level m and level n, where Em > En the atom looses energy equal to Em - En. Since energy is conserved this energy is contained in the photon which is emitted with an energy equal to E = h c/l.


En = -10.97 h c/n2

Em = -10.97 h c/m2

Ep = hv

Final Energy = photon energy + atom energy

E = hc/ -10.97 h c /(n2)

Must equal initial or total energy:

-10.97 h c /(m2)

First 4 shells of a

Hydrogen atom.

Is the quantum Is the quantum nature of atomic nature of atomic

states a little states a little odd?odd?

A note about QMA note about QMImagine if potential energy were quantized!

SummarySummary

Atoms have discrete energy levels, specific Atoms have discrete energy levels, specific to that atom.to that atom.

A photon is absorbed when an electron A photon is absorbed when an electron jumps to a higher energy level.jumps to a higher energy level.

A photon is emitted when an electron drops A photon is emitted when an electron drops to a lower energy level. to a lower energy level.

The emitted/absorbed photon’s energy The emitted/absorbed photon’s energy equals the difference between the atomic equals the difference between the atomic levels involved. levels involved.

Astronomy Astronomy QuestionQuestion

How do we measure the composition of a planet, or extra-solar planet, or star, or galaxy if we’ve never been there

Solar SpectrumSolar Spectrum

Absorption lines appear as hydrogen atoms in the Sun’s atmosphere capture photons and jump to more excited atomic levels.

Atomic ShellsAtomic ShellsThe discrete electron levels are arranged in shells. Each shell has a maximum occupancy.

The first electronic shell can have at most 2 electrons, the second shell has room for 8 electrons and so on.

The 1st shell has the lowest energy. Thus, elements, in their lowest energy state fill the 1st level first, and then fill the 2nd level next. These elements are listed in the 1st and 2nd rows of the periodic table.

Atoms are most stable if their outer shell is full.

The electrons in outer shells are shielded by the inner shells from the full attraction of the nucleus. These electrons participate most readily in chemical reactions.

Atomic ShellsAtomic Shells

How many electrons does neutral Carbon (6 protons) have in its outer shell?

How many electrons does neutral Neon (10 protons) have in its outer shell?

The Periodic TableThe Periodic Table

MoleculMolecularar

SizesSizes

Periodic or Mendelev TablePeriodic or Mendelev Table

Li: solid, Cs: liquid, Ar: gas, Tc:Tc: synthetic

# protons

1 e- in outer shell (Alkali Metals) Full outer shell (Noble Gases)

1 e- missing to fill shell (Halogens)

BondingBonding

There are three major ways that elements bond to form molecules.

Ionic BondsIonic BondsAtoms with filled shells, the Noble Gases, are highly inert.

Atoms with one electron in the outer shell, and atoms with one electron missing are, on the other hand, highly reactive. These atoms form ionic bonds. The alkali gives up an electron. The halogen takes the electron. Elements are bonded by the electric force between the ions.

Example of ionic bondsExample of ionic bonds

Ruby

Sapphire

Aluminum oxide, Al2O3

Metallic BondsMetallic BondsAtoms in a metals also give up electrons, however the electrons are not transferred to the other atom. Instead, the electrons are shared by all the atoms.

The sea of electrons allow current to flow through metal. Metals thus make good conductors.

In sodium, for example, 1 out of the 11 electrons is released so that Na has two filled shells. The extra electrons move around the metal in a “sea” of negative charge. This negatively charged sea moves around a regular structure of positive Na ions.

Covalent BondsCovalent BondsCertain molecules are formed by sharing electrons. The covalent bond that forms resembles metallic bonds in that electrons are shared. Yet, like ionic bonds the electrons are shared in discrete shells of the atoms and don’t run willy nilly throughout the material.

QuestionQuestion

How would you covalently bond two oxygen atoms to make O2? Oxygen has 8 protons & electrons.

How many electrons would each O have to share with the other?


What kind of bonding does KBr have?

# protons



AnswerAnswer

Multiple Multiple Covalent Covalent

BondsBonds

N278%

O221%

H2O 0-4%

Ar 0.9%

CO20.035%

Ne 0.0018%

He 0.0005%

CH40.0001%

H20.00005%

O30.000004%

Earth’s Atmosphere

Gases in Earth’s atmosphere are mainly covalently bonded molecules or noble gases.

Combining C6, N7, O8

Molecular Molecular attractionattraction

ssPolar molecules are more positively charged on one side and more negative on the other. This provides a cohesion.

QuestionQuestion

How would you expect KF to be bonded?


What kind of bonding does KBr have?

# protons



SummarySummaryAtoms have discrete energy levels, specific to that atom.Atoms have discrete energy levels, specific to that atom.A photon is absorbed when an electron jumps to a higher energy level.A photon is absorbed when an electron jumps to a higher energy level.A photon is emitted when an electron drops to a lower energy level. A photon is emitted when an electron drops to a lower energy level. The emitted/absorbed photon’s energy equals the difference between the The emitted/absorbed photon’s energy equals the difference between the

atomic levels involved. atomic levels involved. Atomic levels can only fit a certain number of electrons (2 in the 1Atomic levels can only fit a certain number of electrons (2 in the 1stst level, 8 in level, 8 in

the 2the 2nd nd …)…)The periodic table is arranged according the electronic shells and the The periodic table is arranged according the electronic shells and the

number of protons/electrons in the atom. number of protons/electrons in the atom. Atoms with filled shells are most stable. Atoms bond in order to achieve this Atoms with filled shells are most stable. Atoms bond in order to achieve this

configuration. configuration. Ionic bonding involves the transfer of electrons from one atom to another. Ionic bonding involves the transfer of electrons from one atom to another. Covalent bonding involves the sharing of electrons by one or several atoms.Covalent bonding involves the sharing of electrons by one or several atoms.Metallic bonding involves the sharing of electrons by the entire Metallic bonding involves the sharing of electrons by the entire

material/metal. material/metal.

Radioactive DatingRadioactive Dating

ParentParent

Carbon-14Carbon-14 DaughterDaughter

Nitrogen-14Nitrogen-14 Half LifeHalf Life

5,730 yrs*5,730 yrs*

Potassium-40Potassium-40 Argon-40Argon-40 1.25 billion 1.25 billion yrsyrs

Uranium-238Uranium-238 Lead-206Lead-206 4.5 billion yrs4.5 billion yrs

Thorium-232Thorium-232 Lead-208Lead-208 14 billion yrs14 billion yrs

Rubidium-87Rubidium-87 Strontium-87Strontium-87 48.8 billion 48.8 billion yrsyrs

Samarium-Samarium-147147

Neodymium-Neodymium-143143

106 billion yrs106 billion yrs

Uranium-235Uranium-235 Lead-207Lead-207 704 billion yrs704 billion yrs*Time that it takes wood to have half the C14 of a living plant.

Swisher et al. 1992, Science

Carbon Dating Carbon Dating

1. Solar neutrons enter Earth’s atmosphere.

2. Neutrons collide with N14 (7p, 7n), creating C14 (6p,8n) [n + N14 p + C14 ]

3. Living bodies continually absorb C14 (e.g. as CO2 in photosynthesis).

4. When the plant or animal dies, it no longer assimilates C14.

5. The C14 decays (half life of 5730 yrs). [C14 N14 + e- + ve ] (n p + e- + ve )

6. The e- emission rate reveals the age.

Measure ages < 70,000 yrs

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The Quiz Average (not including zeros): 57. How to improve 1)Review Quiz and mistakes in Quiz. 2)Notice correlation between Quiz & Study Guide 3)Do the