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Things we know… Electrons are negatively charged. Electrons are very small
1/2000 that of a proton or neutron 9.108 X 10-28 grams
Electrons determine the chemical behavior of the atom.
According to Modern Atomic Theory: Electrons move around the nucleus
randomly, billions of times per second.
Not in perfect orbits like seen here in the Bohr Model,
but rather in complex patterns in a space called the “electron cloud.”
The exact location and speed of an electron is never known!!
Electron Energy Levels Atoms have energy levels where electrons
“live”
The further out an energy level is, the more energy an electron has.
Only a certain number of electrons are allowed in each energy level
n = energy level
How many energy levels does Li have?
How many energy levels does Sr have?
Determining Energy Level
Energy Levels = Periods A row on the periodic
table is called a period.
What period is Ca in? Al is in the third
period, how many energy levels does it have?
Energy levels have sublevels called orbitals
Energy levels have 1 to 4 different orbitals.
The orbitals are called S P D F
The periodic table reflects the arrangement.
Larger energy levels have more orbitals.
Besides “s” and “p” orbitals, there are also “d” and “f” orbitals.
Orbitals have different and unusual shapes.
Energy Levels have 1 – 4 orbitals Period 1 has 1
orbital, what is it? Period 2 has 2
orbitals, what are they?
How many orbitals does period 3 have?
Rules for Filling Orbitals with Electrons
Always fill the lowest energy level before going to the next energy level (electrons are lazy!)
Fill all sub-orbitals in an energy level with Only two electrons max. per sub-orbital one electron before pairing electrons up. (electrons are shy!)
Only two electrons max. per sub-orbital
When electrons pair up they have opposite “spins” indicated by an up or a down arrow.(↑ or ↓).
Writing electron configuration Electron configuration
for Helium S-orbitals always fill
first. Each s-orbital can
hold 2 electrons.
Lets Try Another! P orbitals can hold up
to 6 electrons P orbitals only fill
when the s orbital before it has filled
Nitrogen has 7 electrons
Writing Electron Configuration Nitrogen has seven
electrons Neon has ten
electrons How would Ne be
written?
Why do we need this stuff??? To determine the valance electrons
Electrons in the outermost energy level Valance electrons help determine the
chemical activity of the element. How many valance electrons does carbon have?
1s2 2s2 2p2
How many valance electrons does Beryllium have?
1s2 2s2