Chapter 4

Electrons in Atoms

Thomsons’s ModelAtom has postitive

pieces and negative pieces.

Thought they were all mixed up together.

Called a “plum pudding” model.

Rutherford’s Model

• Discovered the nucleus

• Small dense and positive

• Electrons moved around in Electron cloud

Rutherford’s ModelDiscovered the

nucleus Very small and

positively charged Most of the atom

is empty space with electrons moving around

Bohr’s Modelo 2, 8, 8, …thingo Electrons are in “rings” or energy

levels.o Energy separates one level from

another.o Electrons can never be found in

between two levels.

More details about energy levels. All orbits are not sphere-shaped. It can only tell us the

probability of finding an electron a certain distance from the nucleus.

The Modern Model (the Quantum Mechanical Model)

There is one s orbital in every energy level

Sphere shaped

Each s orbital can hold 2 electrons Called the 1s, 2s, 3s, etc.. orbitals.

S orbitals

p orbitalsStart at the second energy level Peanut-shaped 3 different directions Each peanut (orbital) can hold 2

electrons

d orbitalsDaisy shaped (except the 5th picture)

5 d orbitals can hold 10 electronsEach d orbital can hold 2 electrons

f orbitalsStart at the fourth energy level “Funny” shapedEach funny shape holds up to 2

electrons (total= up to14 electrons)

Electron ConfigurationsTells the way electrons are arranged in

atoms. Gives more details than BohrElectrons must fill in this order

1s22s22p63s23p64s23d104p65s24d105p6…

Electron ConfigurationsLowest energy fill first.

The energy levels overlap

(ex: …4s23d104p6…)

Electrons must fill the spaces in order and cannot leave any empty spaces

This is called the Aufbau Principle

Orbital NotationStart with electron configuration and

add one box for every orbital.Show electrons by putting arrows in the

boxes. (Pointing opposite ways.)

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d4

Orbital NotationNotice in the last box the electrons

spread out before doubling up.

This is Hund’s Rule (=bus rule)

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d4

Orbital NotationNotice that only the boxes of the last

part (4d4) can have empty spaces.They have to be filled in order according

to the Aufbau Principle1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d4

Pauli Exclusion PrincipleThe 2 arrows have to point opposite ways.Two electrons in the same orbital (box)

must be spinning in opposite directions according to the Pauli

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d4