Electron Configuration

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.

Energy levels can hold a certain number of electrons

2

8

8

Energy levels have sublevels called “orbitals.”

S Orbitals

P Orbitals

We will work with two types:

S Orbitals can hold 2 electrons

P Orbitals can hold 6 electrons

Add up electrons the orbitals hold and you know how many electrons the energy level can hold.

2

8

8

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?

END

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

Those Crazy Electrons!

S Orbitals are sphere-shaped.

P Orbitals are dumbbell-shaped.

d & f Orbitals have wild shapes.

A Copper atom simulation!

What are Orbitals? The places electrons

probably are- They look like

Spheres Dumbbells Donut things…