Electrons in the Atom Chapter 5

Rutherford to Bohr Rutherford’s model had the correct particles of the atom But could not explain the properties of elements. Niels Bohr proposed that electrons moved in circular orbits around the nucleus. Each orbit distance has a certain amount of energy. “Energy levels”

A Reminder: Potential Energy Potential energy is the energy of position. Energy can be stored by raising a mass. PE = (mass)x(gravity)x(height) It takes energy to go up Energy is released when things go down

The Bohr Model Electrons move in Energy Level “orbits” Like the rungs of a ladder You can go up Takes energy to do it You can go down Energy is lost Bohr noticed that it was only certain amounts of energy could be released “Quantums” of certain quantities of energy.

http://www.youtube.com/watch?v=45KGS1Ro-sc&feature=related

http://phet.colorado.edu/en/simulation/hydrogen-atom

Bohr solves one problem, has his own Bohr’s model perfectly predicts the behavior of the hydrogen atom The simplest atom, with only one electron But not any others! Schrödinger gives up on the idea of the electron as a particle, and says “It’s a wave of probability!” LOL PWND, Bohr!

http://www.youtube.com/watch?v=Nv1_YB1IedE&feature=related 11:15 then Go to Vegas

The Quantum Mechanical Model Schrödinger describes electrons as a wave Shows electrons do have certain quantities, you just don’t know exactly where the electrons are. You can determine where the electrons PROBABLY are (in a certain volume) but can’t be 100% sure. Creates “orbitals” of probability where electrons probably are.

The World’s Weirdest Hotel 4 floors Not well designed.

Atomic Orbitals Electrons are found in orbitals of probability These orbitals each have an energy level (like Bohr said) with different amounts of energy Each energy level has sub-levels of energy Level 1 = 1 sublevel Level 2 = 2 sublevels Level 3 = 3 sublevels Level 4 = 4 sublevels

The 4 energy levels. Level 1 (n=1) – s sub-level Level 2 (n=2) – s and p sub-levels Level 3 (n=3) – s, p, and d sub-levels Level 4 (n=4) – s, p, d, and f sub-levels s, p, d, and f are sets of shapes (orbitals) s = 1 orbitals (sphere) p = 3 orbitals (x, y, and z buns) d = 5 orbitals f = 7 orbitals

Where the electrons go. The way the electrons are arranged is the electron configuration Configurations follow three rules: Aufbau principle The Pauli exclusion principle Hund’s rule

Aufbau Principle “Electrons are lazy” Electrons will automatically go to the lowest energy sub-level available 1s then 2s then 2p then 3s then 3p then 4s then 3d then 4p

Pauli Exclusion Principle “Electrons don’t like similar electrons.” Electrons have two spins (up and down or clockwise and counterclockwise) Only two electrons may fit in each orbital One can spin each direction, and you can’t fit two electrons spinning the same ways. Ex) 1s has 1 orbital, so it can fit 2 electrons Ex) 2p has 3 orbitals, so it can fit 6 electrons

Hund’s Rule “Electrons hate each other.” Electrons will fill unfilled orbitals before sharing orbitals with other electrons Fill up all the available orbitals on the sub-level with electrons before “doubling up”

Two Ways to show the electrons Electron Orbital Drawing Shows the orbitals the electrons are in and the spin of the electrons Electron configuration Writes out the energy level, sub-level, and the number of electrons in each

Practice, Practice, Practice Okay, let’s start with Hydrogen

Practice, Practice, Practice Okay, let’s start with Hydrogen 1s1

More practice Now Carbon!

More practice Now Carbon! Atomic number: 6 Electrons: 6 (because it’s neutral)

More practice Now Carbon!

Try it now Potassium? Manganese?

Try it now Potassium? Manganese? 1s2 2s2 2p63s2 3p64s2 3d5

Solving Electron Configurations What is it?

Solving Electron Configurations What is it? Sodium (hint: count the electrons)

What is it? 1s22s22p63s23p64s23d9

What is it? 1s22s22p53s23p64s23d5 You’ll never catch me alive, COPPER!!!

Make one up on your own. Show it to your buddy or buddies.

Can they figure it out?

There are some exceptions to the rules… Sometimes the actual electron configurations aren’t the same as you would assign according to the aufbau principle. Sometimes it is more stable to fill the d sub-level rather then the s sub-level first EX) Cu and Cr It’s not important to know WHICH exceptions there are, but just to know they exist

Light is a lot like an electron It travels as a wave, but can also be measured as particles Particle-wave duality Most of what we know about electrons, we know because of the light they produce

Property of (Light) Waves Waves have: Amplitude The height of the wave Wavelength (λ) The distance from one wave to the next (measured from crest to crest) Measured in meters or nm Frequency (ν) The number of waves per second passed a point Measured in Hertz (same as “per second”)

https://www.youtube.com/watch?v=7Iv4GmyXsCQ

Wavelength and frequency… When wavelength is higher (longer), frequency becomes lower (slower). When wavelength gets lower (shorter), frequency becomes higher (faster). When you multiply wavelength (m) times frequency (1/s) you always get the same speed! 2.998 x108 m/s = c

Okay, let’s give it a shot! We have a wave with a length of 2.0m (about 6’6”). What is the frequency of that wave? Remember: c= λ* ν Or the speed of light = wavelength times frequency So, 2.998x108 m/s = 2m * ν

Okay, let’s give it a shot! We have a wave with a length of 2.0m (about 6’6”). What is the frequency of that wave? Remember: c= λ* ν Or the speed of light = wavelength times frequency So, 2.998x108 m/s = 2m * ν ν = (2.998x108)/2 ν = 1.499x108 ν = 1.5 x108 Hz (or 1/s) (correct significant figures)

Okay, let’s try another My favorite radio station growing up was 107.7 (KNDD The End). It broadcasts at 107.7 MHz. What is its wavelength?

Okay, let’s try another My favorite radio station growing up was 107.7 (KNDD The End). It broadcasts at 107.7 MHz. What is its wavelength? λ = 2.998x108 107.7 MHz

Okay, let’s try another My favorite radio station growing up was 107.7 (KNDD The End). It broadcasts at 107.7 MHz. What is its wavelength? λ = 2.998x108 m/s * 1 MHz = 107.7 MHz 1,000,000 Hz 2.784 m! (About 8 feet long!)

http://www.youtube.com/watch?v=cfXzwh3KadE

The Electromagnetic Spectrum Electromagnetic radiation is made of waves. Divided into the electromagnetic spectrum Going from longest (and lowest frequency) to shortest (highest frequency): Radio waves Radar Microwaves Infrared Visible Ultraviolet (UV) X-rays Gamma rays

The Visible Spectrum The visible spectrum starts at the edge of the infrared and goes to the ultraviolet “ROY G. BIV” (from low to high frequency, and low to high energy) Red Orange Yellow Green Blue Indigo Violet

Atomic Spectra When you run light through a prism, it separates the light into its colors Which can be individual colors (in bands) or all colors (in a rainbow) “A spectrum” When atoms absorb energy electrons move to higher energy levels When they lose energy (and go to a lower energy level) they release the energy in the form of light. Creates its “atomic emission spectrum”

http://www.youtube.com/watch?v=QI50GBUJ48s

Why does the emission spectrum happen? Electrons start at their “ground state” (from the aufbau configuration) Give them some energy, and they jump to other orbitals and energy levels The amount of energy the electron releases is proportional to the frequency of energy of the light it releases! Can be calculated by E = hν h = 6.626x10-34 J*s

Calculating the energy of light Using E=hν allows us to calculate one “photon” of energy Will not be very much Allows us to see how much one type of light has compared to another Remember h = 6.626x10-34 J*s Let’s try it…. How much energy is in a wave with a frequency of 106,100,000 Hz (106.1 on the radio)? E h v

Calculating the energy of light Using E=hν allows us to calculate one “photon” of energy Will not be very much Allows us to see how much one type of light has compared to another Remember h = 6.626x10-34 J*s Let’s try it…. How much energy is in a wave with a frequency of 106,100,000 Hz (106.1 on the radio)? E = (6.626x10-34 j*s)(106,100,000/s) E h v

How much energy? 7.030x10-26 J! Not much, but that’s for ONLY ONE PHOTON from one atom! A photon is one quantum of light energy when it acts as a particle.

Two equations to figure out 3 numbers! E=h ν c = λ ν c = 3.00x108 m/s h = 6.626x10-34 J*s As long as you have one number, you can solve for any of the other two unknowns!

What has more energy, 106.1 or blue light (475 nm)? We know that 106.1Mhz is 7.030x10-26 J! What is 475nm? Determine the frequency, and THEN determine the energy. c = λ ν Then E=h ν

Quantum Mechanics Classical (Newtonian) mechanics describe objects larger than atoms “Makes sense” to us, because it’s what we see most days. Quantum mechanics describes the motion of subatomic particles and atoms Doesn’t “make sense” All matter can be described as waves! Heisenberg uncertainty principle It is impossible to know the velocity AND a position of a particle. It cannot be observed because the act of observing it moves the particle.