Electron Configuration

Chapter 3 Section 3.2

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 travel around the nucleus

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 of an electron is never known!!

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? Overhead notes here

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 orbitals hold and you know how many electrons the 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 unusual shapes.

S Orbitals are sphere-shaped.

P Orbitals are dumbbell-shaped.

d & f Orbitals have wild shapes.

A Copper atom simulation!

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.

What are Orbitals? The places electrons

probably are- They look like

Spheres Dumbbells Donut things…Ab

roller

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?

A. General Rules Pauli Exclusion Principle

Each orbital can hold TWO electrons with

opposite spins. We note this with two arrows

going in the opposite directions. You can use

any symbol you choose but use something.

A. General Rules Aufbau Principle

Electrons fill the lowest energy orbitals first.

“Lazy Tenant Rule” You see the ground floor is easy but climbing the stairs is hard work!

Ground Floor

RIGHTWRONG

A. General Rules Hund’s Rule

Within a sublevel, place one e- per orbital before pairing them.

“Empty Bus Seat Rule”

O 8e-

Orbital Diagram

Electron Configuration

1s2 2s2 2p4

B. Notation

1s 2s 2p

Shorthand Configuration

S 16e-

Valence Electrons

Core Electrons

S 16e- [Ne] 3s2 3p4

1s2 2s2 2p6 3s2 3p4

B. Notation Longhand Configuration

s-block

1st Period

1s1 1st column of s-block

C. Periodic Patterns Example - Hydrogen

1

2

3

4

5

6

7

C. Periodic Patterns Shorthand Configuration

Core e-: Go up one row and over to the Noble Gas.

Valence e-: On the next row, fill in the # of e- in each sublevel.

Writing electron configuration 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

1s2 2s2 2p3

Writing Electron Configuration Nitrogen has seven

electrons 1s2 2s2 2p3

Neon has ten electrons

How would Ne be written?

1s2 2s2 2p6

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.(Its attitude) How many valance electrons does carbon have?

1s2 2s2 2p2

How many valance electrons does Beryllium have?

1s2 2s2

Those Crazy Electrons!