Honors Chemistry
unit 2: Atomic Structure Notes
What is atomic structure? What is an isotope?
Dogs Teaching Chemistry https://www.youtube.com/watch?v=addK0b2Isw8
What really is an atom?
An atom is the defining structure of an element , which cannot be broken by any chemical means. A typical atom consists of a nucleus of protons and neutrons with electrons orbiting this nucleus.
| Proton | Neutron | Electron |
Charge | +1 | 0 | -1 |
Location | Nucleus | Nucleus | Orbiting Nucleus |
Importance | Identity of Atom | Keeps the atom stable | Bonding |
Atomic Number
Mass Number
Net Charge
= # of Protons
= # of protons + # of neutrons
= # of protons - # of electrons
Write the correct symbol in the correct notation for a neutral atom who's atomic number= 17 and has 18 neutrons.
Isotope = atoms with the same atomic number but different mass numbers
Considering subatomic particles this means, Isotopes have the same number of but different numbers of .
Hydrogen Deuterium Tritium
On the periodic table, the number we see, is not actually the mass number but the average atomic mass.
The average atomic mass accounts for the average mass of all atoms in existence for a particular element.
What is interesting about the mass numbers on the periodic table?
How do we find the average of something?
Thankfully we don’t have to find every little atom, but it on a scale weigh it and add them all up and divide by how much there are. (That would take forever).
What we do instead, is use this nice little thing called abundance. Abundance is a percentage of the total number of atoms that an isotope makes up.
Carbon has 3 different isotopes with mass numbers 12, 13, and 14. What is its average atomic mass?
(The abundances of these isotopes, are 99% carbon-12, 1% carbon-13, and because the abundance of carbon-14 is so tiny, we wont consider it in our calculations.)
Average atomic mass = (Mass x abundance) + (Mass x abundance)
100
Honors Chemistry
unit 2: Nuclear Chemistry Notes
What is happens during nuclear decay?
Fission
Alpha decay is when a helium nuclei comes flying off a larger nucleus. These helium nuclei are called alpha particles and are represented by this:
Beta decay is when an electron flies of another nucleus. The electron in this instance is called a beta particle and is represented by this:
Gamma decay when a very high energy of light is emitted from a nucleus. This light is called a gamma ray and is represented by this:
Half life is the amount of time is taken for half of a sample to decay.
Barium-122 has a half-life of 2 minutes. A fresh sample weighing 80 g was obtained. If it takes 10 minutes to set up an experiment using barium-122, how much barium-122 will be left when the experiment begins?
Time: | 0 min | 2 min | 4 min | 6 min | 8 min | 10 min |
Mass: | | | | | | |
Honors Chemistry
unit 2: Atomic Theory & The Bohr Model Notes
What is atomic theory? How can we use the Bohr Model?
Atomic Theory: Who said what?
John Dalton: Speculated that we were made up of small particles called atoms. He believed these atoms were very small hard sphere balls, kind of like Pool Balls.
J. J. Thompson: Used a cathode ray tube. Discovered subatomic particles, one of positive charge (the proton), and one of negative charge (the electron). He believed these particles floated around in a soup of matter that was the atom.
Ernest Rutherford: Discovered the neutron (a neutrally charged particle), with his Gold Foil Experiment. Rutherford’s model predicted that electrons are distributed around a central nucleus filling up the entire space of the atom.
Atomic Theory: Who said what?
Niels Bohr: Stated that most of the atom was actually empty space. Besides a central nucleus and few very tiny electrons that orbited the nucleus at different energy levels called quanta.
Erwin Schrödinger: Discovered the electron cloud model. This model predicts that electrons are not located in an exact position but instead move from many different positions very rapidly, making a cloud of where an electron may be at a given moment.
Atomic Theory: Who said what?
Why is the Bohr model useful?
DISCLAIMER: While we know today that the exact location of the electrons around the nucleus is unknown, this model was extremely important to understanding the energy of electrons and the spectra created by certain atoms. Electrons may not be “orbiting the nucleus” at an exact location, but electrons do exist at specific energies. Because of this we can use the Bohr model to visualize what the electrons are doing.
Niels Bohr believed that the electrons orbited the nucleus in rings called orbitals. These orbitals existed at specific distances away from the nucleus. Bohr believed that electrons moved between their home or ground state location in a certain orbital and a high energy state at another orbital by absorbing and emitting energy in the form of light.
“It allows us to visualize complicated things. Electrons start out in ground states, move to excited states, and then give off light when they return. Though the electrons aren’t actually jumping up and down, their energies are increasing and decreasing as this happens. The Bohr model, though incorrect, allows us to visualize what’s happening more easily.” -Chemfiesta.com
Each possible electron orbit in Bohr’s model has a fixed energy. These are energy levels.
A quantum of energy is the amount of energy required to move an electron from one energy level to another energy level.
n stands for the energy level.
1 photon = 1 quantum of light
n=1
n=1
n=2
n=3
n=2
n=3
emits photon
absorbs
photon
The light that is emitted by an electron falling from an excited state to a ground state depends on the orbitals it travels to and from. Just like you need more energy in your car to get from your home to wilmington than from your home to school.
What wavelength of light is emitted from a n=6 to n=2??
What wavelength of light is emitted from a n=6 to n=2??
Honors Chemistry
unit 2: EMS Spectrum Math
How are wavelength, frequency and energy related? How can we calculate them?
Everything is related
But how????
The light you see is actually coming at you just like this wave.
↲
Infrared in snakes:
Radio wave image of �Antennae Galaxies
70 million light years �away
X-ray Image
of the Sun
Wavelength: the distance from one peak to the next peak.
Frequency: The number of wave peaks that pass through a point in a certain amount of time.
As Wavelength....______________
Frequency...._______________
λν = c
λ=wavelength
ν= frequency
c= speed of light (3.00 x 108 m/s)
`
What is the frequency of EMR having a wavelength of 555 nm? (EMR is an abbreviation for electromagnetic radiation.)
What is the wavelength (in nm) of EMR with a frequency of 4.95 x 1014 s¯1?
What is the wavelength (in nm) of EMR with a frequency of 4.95 x 1014 s¯1?
As Frequency....______________
Energy...._________________
E = hν
E = energy
ν= frequency
h= planks constant (6.626 x 10¯34 Joule*second)
How many Joules of energy are contained in a photon with λ = 550 nm?
Honors Chemistry
unit 2: Spectroscopy
What are spectra? How can we use an element’s spectra to calculate the wavelength, frequency, & energy?
Yesterday we talked about the Bohr Model and how electrons move from lower to higher energy states and vice versa. And while it might not happen in the exact way Mr. Bohr explained via orbitals, it does happen, and light is emitted. We can study this emission/absorption of light in something called the electromagnetic spectrum in a process called spectroscopy.
Spectroscopy goes like this:
Step 1: Add energy to your sample.
Step 2: This will cause something in the sample to go from a lower energy ground state into a higher energy excited state.
Step 3: When the sample reverts to the lower energy ground state, the energy that it absorbed will be given off.
Because everything has different energies at which this happens, you can use this unique spectrum to figure out what the sample is.
We can use the light we see to figure out the wavelength of light that is being emitted. This is super important because as we learned, light and energy is related!
Continuous spectrum: Contains all wavelengths of visible light
Emission spectrum: Contains only wavelengths of visible light emitted by an excited electron returning to a lower energy state.
Absorption spectrum: Contains all BUT the wavelengths of visible light absorbed by electrons going to higher energy levels.
Longer Wavelength
Shorter Wavelength
Each element has specific color of light that they give off when their electrons transition from the excited state to ground state. We can arrange these lights in something called a spectrum.
All elements have unique line spectra because all elements have different allowed energies for the ground and excited states. This makes it possible for us to identify elements based on their line spectra, a process known as spectroscopy.
Since each color of light is related to a specific wavelength, we can use the spectra to find out the wavelengths that certain elements reveal.
However, its hard for us to see the spectra when we look right at something, because the way our eyes work. We can use something called a spectroscope to help us view the spectrum.
Honors Chemistry
unit 2: Quantum Theory
What is quantum theory? How can we use quantum theory to explain the organization of electrons?
Your hotel looks like the diagram below:
6th floor ________ ________ ________ _______ _________
5th floor ________ ________ _________
4th floor _________
3rd floor ________ ________ _________
2nd floor _________
1st floor __________
(1) Compare this with the Hog Hilton. What are the similarities and the differences?
(2) To go between floors on the Hog Hilton did the hogs need to use energy?
Would electrons need to use energy to go between orbitals?
(3) If only ½ the energy necessary to go between the 1s and 2s orbital is available, will an electron go to the 2s orbital?
In Hog Hilton you learned how to fill up an imaginary hotel. Now we can relate this example to electron orbitals. Electron orbitals are modeled by the picture below and are grouped into principal energy levels, just like the hilton was organized by floors.
3d ___ ___ ___ ___ ___ n=3
4s ____ n=4
3p ___ ___ ___ n=3
3s ___ n=3
2p ___ ___ ___ n=2
2s ___ n=2
1s ___ n=1
Aufbau Principle: lower energy levels fill first.
Pauli Exclusion Principle: All electrons in singly occupied orbitals must have the same spin. When two electrons occupy an orbital they have opposite spins.
Hund's Rule: electrons will spread out to fill all available space before doubling up.
1) Hogs are lazy and do not want to walk up the stairs!
2) Hogs can’t stand each other except when rule #1 forces them to put up with each other.
3) If hogs are in the same room they will face in opposite directions.
4) They stink, so you can’t put more than two hogs in each room.
While Hogs only had floors 1, 2, 3..... Electron Orbitals are a bit more complicated. They fill in this order below!
Thank goodness we don't have to remember the order because we can just follow the periodic table!
(1) 7 electrons
3d ___ ___ ___ ___ ___ n=3
4s ____ n=4
3p ___ ___ ___ n=3
3s ___ n=3
2p ___ ___ ___ n=2
2s ___ n=2
1s ___ n=1
(2) 16 electrons
3d ___ ___ ___ ___ ___ n=3
4s ____ n=4
3p ___ ___ ___ n=3
3s ___ n=3
2p ___ ___ ___ n=2
2s ___ n=2
1s ___ n=1
What element is this?
4f ___ ___ ___ ___ ___ ___
6s ___
5p ___ ___ ___
4d ___ ___ ___ ___ ___
5s ___
4p ___ ___ ___
3d ___ ___ ___ ___ ___
4s ____
3p ___ ___ ___
3s ___
2p ___ ___ ___
2s ___
1s ___
Bad News: Electron orbital filling diagrams are tedious.
Good News: Some other guys thought so too because they found a way to abbreviate the filling with something called electron configurations.
For the electron configuration all we have to do is write out each of the orbitals with a little number in the superscript denoting how many electrons are in that orbital.
1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f
*Check at the end to make sure all the superscripts add up to the elements atomic number
To make it even easier we can go from this......
1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f
to this!
[Kr] 5s 4d 5p 6s 4f
⤶