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**Chapter 5 “Electrons in Atoms”**

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**Ernest Rutherford’s Model**

Discovered dense + piece at nucleus Electrons move around it, like planets around sun Mostly empty space Didn’t explain chemical properties of elements

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**Niels Bohr’s Model Why don’t electrons fall into nucleus?**

Move like planets around sun. specific circular orbits at different levels. An amount of fixed energy separates one level from another.

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**The Bohr Model of the Atom**

I pictured the electrons orbiting the nucleus much like planets orbiting the sun. However, electrons are found in specific circular paths around the nucleus, and can jump from one level to another. Niels Bohr

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**Bohr’s model Energy level measure of fixed energy e- can have**

Like rungs of ladder e- can’t exist between energy levels can’t stand between rungs on ladder Unlike ladder, energy levels not evenly spaced Higher energy levels closer together – less energy needed for jump

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**The Quantum Mechanical Model**

Energy is “quantized” - in chunks. A quantum is exact energy needed to move e- one energy level to another. Since energy of atom is never “in between” quantum leap in energy must exist. Erwin Schrodinger (1926) derived equation described energy and position of e- in an atom Schrodinger

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**The Quantum Mechanical Model**

Very small things behave differently from big things quantum mechanical model is a mathematical solution not like anything you can see (like plum pudding!)

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**The Quantum Mechanical Model**

Has energy levels for e- Orbits not circular. only tells us probability of finding e- a certain distance from nucleus.

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**The Quantum Mechanical Model**

e- found inside blurry “electron cloud” (area where there’s chance of finding e- Like fan blades or bicycle wheel

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Atomic Orbitals Principal Quantum Number (n) = the energy level of e- (1, 2, 3, etc.) Within each energy level, Schrodinger’s equation describes several shapes. called atomic orbitals - regions of space w/ high probability of finding e- Sublevels like rooms in a hotel letters s, p, d, and f

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**Principal Quantum Number (n)**

denotes the energy level (shell) e- is located. Maximum number of e- that can fit in energy level is: 2n2 How many e- in level 2? level 3?

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**First possible energy level**

Individual orbitals First possible energy level Maximum electrons # of orbitals s spherical 2 1 1st p dumbell 3 6 2nd d clover leaf 10 5 3rd f complicated 7 14 4th

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**By Energy Level Energy Level 2 (n=2) Has s and p sublevels available**

2s (1 orbital) w/ 2 e- 2p (3 orbitals) w/ 6 e- 2s22p6 8 total e- Energy Level 1 (n=1) Has only s sublevel 1s (1 orbital) w/ only 2 e- 2 total e- 2 2 6

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**By Energy Level Energy level 4 (n=4) Energy level 3 (n=3)**

s, p, d, and f sublevels 4s (1 orbital) w/ 2 e- 4p (3 orbitals) w/ 6 e- 4d (5 orbitals) w/ 10 e- 4f (7 orbitals) w/ 14 e- 4s24p64d104f14 32 total e- Energy level 3 (n=3) s, p, and d sublevels 3s (1 orbital) w/ 2 e- 3p (3 orbitals) w/ 6 e- 3d (5 orbitals) w/ 10 e- 3s23p63d10 18 total e- 2 2 6 6 10 14 10

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**By Energy Level Any more than the fourth and not all orbitals fill up.**

You simply run out of e-’s orbitals do not fill up in neat order. energy levels overlap Lowest energy fill first. s and p orbitals 1:20 d orbitals 3:40

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**Summary of Principal Energy Levels, Sublevels, and Orbitals**

Number of sublevels Type of sublevel Max # of electrons Electron configuration n = 1 1 1s (1 orbital) 2 1s2 n = 2 2s (1 orbital 2p (3 orbitals) 8 2s2 2p6 n = 3 3 3s (1 orbital) 3p (3 orbitals) 3d (5 orbitals) 18 3s2 3p6 3d10 n = 4 4 4s (1 orbital) 4p (3 orbitals) 4d (5 orbitals) 4f (7 orbitals) 32 4s2 4p6 4d10 4f14

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**Electron distribution in an Atom**

Energy Level 3d 3 3p 3s ENERGY 2 2p 2s 1 1s NUCLEUS

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**Section 5.2 Electron Arrangement in Atoms**

OBJECTIVES: Describe how to write the electron configuration for an atom.

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**Section 5.2 Electron Arrangement in Atoms**

OBJECTIVES: Explain why the actual electron configurations for some elements differ from those predicted by the aufbau principle.

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**Increasing energy 7p 6d 5f 7s 6p 5d 6s 4f 5p 4d 5s 4p 3d 4s 3p 3s 2p**

aufbau diagram - page 133 Aufbau is German for “building up”

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**Electron Configurations…**

…the way electrons arranged in various orbitals around nuclei of atoms. Three rules tell us how: Aufbau principle - electrons enter the lowest energy first. causes difficulties b/c overlap of orbitals of different energies – follow diagram! Pauli Exclusion Principle - 2 electrons max per orbital (hotel room) - different spins

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**Pauli Exclusion Principle**

No two electrons in an atom can have the same four quantum numbers. To show the different direction of spin, a pair in the same orbital is written as: Wolfgang Pauli

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Quantum Numbers Each electron in an atom has a unique set of 4 quantum numbers which describe it. 1) Principal quantum number 2) Angular momentum quantum number 3) Magnetic quantum number 4) Spin quantum number

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**Electron Configurations**

Hund’s Rule- When electrons occupy orbitals of equal energy, they don’t pair up until they have to. write e- configuration for Phosphorus We need to account for all 15 e-’s in phosphorus

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**Increasing energy 7p 6d 5f 7s 6p 5d 6s 4f 5p 4d 5s 4p 3d 4s 3p**

The first two electrons go into the 1s orbital Notice the opposite direction of the spins only 13 more to go...

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**Increasing energy 7p 6d 5f 7s 6p 5d 6s 4f 5p 4d 5s 4p 3d 4s 3p 3s**

The next electrons go into the 2s orbital

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**Increasing energy The next electrons go into the 2p orbital**

3d 4d 5d 7p 6d 4f 5f The next electrons go into the 2p orbital only 5 more...

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**Increasing energy The next electrons go into the 3s orbital**

2p 3p 4p 5p 6p 3d 4d 5d 7p 6d 4f 5f The next electrons go into the 3s orbital only 3 more...

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**Increasing energy 7p 6d 5f 7s 6p 5d 6s 4f 5p 4d 5s 4p 3d 4s 3p 3s 2p**

The last three electrons go into the 3p orbitals. They each go into separate shapes (Hund’s) 3 unpaired electrons = 1s22s22p63s23p3 Orbital notation

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Stairstep pattern

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**An internet program about electron configurations is:**

(Just click on the above link) I electron config 3:24

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**Orbitals fill in an order**

Lowest energy higher energy. Adding e-’s changes energy of orbital. Full orbitals are best situation. half filled orbitals lower energy, next best more stable. Changes filling order

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**Write the electron configurations for these elements:**

Titanium - 22 electrons 1s22s22p63s23p64s23d2 Vanadium - 23 electrons 1s22s22p63s23p64s23d3 Chromium - 24 electrons 1s22s22p63s23p64s23d4 (expected) But this is not what happens!!

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**Chromium is actually: 1s22s22p63s23p64s13d5 Why?**

This gives us two half filled orbitals (the others are all still full) Half full is slightly lower in energy. The same principal applies to copper.

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**Copper’s electron configuration**

Copper has 29 electrons so we expect: 1s22s22p63s23p63d94s2 But the actual configuration is: 1s22s22p63s23p63d104s1 This change gives one more filled orbital and one that is half filled. Remember these exceptions: d4, d9

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**Irregular configurations of Cr and Cu**

Chromium steals a 4s electron to make its 3d sublevel HALF FULL Copper steals a 4s electron to FILL its 3d sublevel

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**Section 5.3 Physics and the Quantum Mechanical Model**

OBJECTIVES: Describe the relationship between the wavelength and frequency of light.

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**Section 5.3 Physics and the Quantum Mechanical Model**

OBJECTIVES: Identify the source of atomic emission spectra.

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**Section 5.3 Physics and the Quantum Mechanical Model**

OBJECTIVES: Explain how the frequencies of emitted light are related to changes in electron energies.

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**Section 5.3 Physics and the Quantum Mechanical Model**

OBJECTIVES: Distinguish between quantum mechanics and classical mechanics.

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**Light Study of light led to development of quantum mechanical model.**

Light is electromagnetic radiation. EM radiation: gamma rays, x-rays, radio waves, microwaves Speed of light = x 108 m/s abbreviated “c” “celeritas“ Latin for speed All EM radiation travels same in vacuum

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- Page 139 “R O Y G B I V” Frequency Increases Wavelength Longer

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Parts of a wave Crest Wavelength Amplitude Origin Trough

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**Electromagnetic radiation propagates through space as a wave moving at the speed of light.**

Equation: c = c = speed of light, a constant (2.998 x 108 m/s) (lambda) = wavelength, in meters (nu) = frequency, in units of hertz (hz or sec-1)

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**Wavelength and Frequency**

inversely related one gets bigger, other smaller Different frequencies of light different colors wide variety of frequencies (spectrum)

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- Page 140 Use Equation: c =

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Low Energy High Energy Radiowaves Microwaves Infrared . Ultra-violet X-Rays GammaRays Low Frequency High Frequency Long Wavelength Short Wavelength Visible Light

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Long Wavelength = Low Frequency Low ENERGY Short Wavelength = High Frequency High ENERGY

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**Atomic Spectra White light all colors of visible spectrum.**

prism separates it.

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**If the light is not white**

heating gas with electricity will emit colors. Passing this light through prism different.

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**Atomic Spectrum Each element gives off own characteristic colors.**

This is how we know composition of stars

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**atomic emission spectrum**

Unique to each element, like fingerprints! ID’s elements

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**Light is a Particle? Energy is quantized. Light is energy…..**

light must be quantized photons smallest pieces of light Photoelectric effect – Matter emits e- when it absorbs energy Albert Einstein Nobel Prize in chem Energy & frequency: directly related.

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**E = Energy, in units of Joules (kg·m2/s2)**

energy (E ) of electromagnetic radiation is directly proportional to frequency () of radiation. Planck-Einstein Equation: E = h E = Energy, in units of Joules (kg·m2/s2) (Joule is metric unit of energy) h = Planck’s constant (6.626 x J·s) (reflecting sizes of energy quanta) = frequency, in units of hertz (hz, sec-1)

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**c = E = h The Math in Chapter 5 Put these on your 3 x 5 notecard!**

There are 2 equations: c = E = h Put these on your 3 x 5 notecard!

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Examples What is the wavelength of blue light with a frequency of 8.3 x 1015 hz? What is the frequency of red light with a wavelength of 4.2 x 10-5 m? What is the energy of a photon of each of the above?

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**Explanation of atomic spectra**

electron configurations written in lowest energy. energy level, and where electron starts from, called it’s ground state - lowest energy level.

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Changing the energy Let’s look at a hydrogen atom, with only one electron, and in the first energy level.

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Changing the energy Heat, electricity, or light can move electron up to different energy levels. The electron is now said to be “excited”

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Changing the energy As electron falls back to ground state, it gives energy back as light

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Experiment #6, page 49-

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**Changing the energy may fall down in specific steps**

Each step has different energy

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**{ { { Balmer series (visible) Paschen series Lyman series (UV)**

(infrared) { { {

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**further they fall, more energy released = higher frequency **

Ultraviolet Visible Infrared further they fall, more energy released = higher frequency orbitals also have different energies inside energy levels All electrons can move around.

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**= h/mv (from Louis de Broglie)**

What is light? Light is a particle - it comes in chunks. Light is a wave - we can measure its wavelength and it behaves as a wave combine E=mc2 , c=, E = 1/2 mv2 and E = h, then we can get: = h/mv (from Louis de Broglie) Calculates wavelength of a particle. called de Broglie’s equation He said particles exhibit properties of waves

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**Wave-Particle Duality**

J.J. Thomson won the Nobel prize for describing the electron as a particle. His son, George Thomson won the Nobel prize for describing the wave-like nature of the electron. The electron is a particle! The electron is an energy wave!

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**Confused? You’ve Got Company!**

“No familiar conceptions can be woven around the electron; something unknown is doing we don’t know what.” Physicist Sir Arthur Eddington The Nature of the Physical World 1934

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**The physics of the very small**

Quantum mechanics explains how very small particles behave Quantum mechanics is an explanation for subatomic particles and atoms as waves Classical mechanics describes the motions of bodies much larger than atoms

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**Heisenberg Uncertainty Principle**

impossible to know exact location and velocity of particle better we know one, less we know other Measuring changes properties. True in quantum mechanics, but not classical mechanics

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**Heisenberg Uncertainty Principle**

“One cannot simultaneously determine both the position and momentum of an electron.” You can find out where the electron is, but not where it is going. OR… You can find out where the electron is going, but not where it is! Werner Heisenberg

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**It is more obvious with the very small objects**

To measure where e-, we use light But light energy (photon) moves e- due to small mass And hitting e- changes frequency of light

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**After Before Photon wavelength changes Photon Moving Electron**

Electron velocity changes Fig. 5.16, p. 145

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End of Chapter 5

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