Electrons and Ionisation Energy

Atomis orbital

A region of space around the nucleus that can hold up to 2 electrons, with opposite spin

What is the shape of a s-orbital?

Spherical

What is the shape of a p-orbital?

Dumbell

Sub-shell

A group of orbitals with the same shape within a shell

What is the order for filling for sub-shells?

1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶

How are electrons paired?

With opposite spin

Why are orbitals of the same energy (snd shell) occupied singly first?

To reduce repulsion

First ionisation energy

The energy required to remove one electron from each atom in one mole of gaseous atoms, to form one mole of gaseous 1+ ions.

What are the first and second ionisation energies for sodium?

First ==> Na_(g) ——> Na⁺_(g) + e^-

Second ==> Na⁺_(g) ——> Na²⁺_(g) + e^-

What factors affect Ionisation energy?

• Atomic radius - greater atomic radius = less nuclear attraction - greatest affect on nuclear charge.

• Nuclear charge - greater nuclear charge = greater nuclear attraction.

• Electron shielding - greater electron shielding = less nuclear attraction, can only be done by full shells.

What factors affect atomic radius?

• Nuclear charge - greater nuclear charge = smaller atomic radius

• Electron shielding - greater electron shielding = greater atomic radius

• Remember to state overall affect to nuclear attraction

What happens to first ionisation energy as you go down a group?

• Nuclear charge increases

• Electron shielding increases

• Atomic radius increases

• Nuclear attraction decreases

• First ionisation energy decreases

What happens to first ionisation energy as you go across a period?

• Nuclear charge increases

• Electron shielding stays the same

• Atomic radius decreases

• Nuclear attraction increases

• First ionisation energy increases

Why do successive ionisation energies always increase?

As each electron is removed, the outer shell electron is drawn closer to the nucleus (atomic radius decreases). The nuclear attraction is greater so more energy is needed to remove the next electron.

What is the general trend in first ionisation energies across a period?

General increase

What is the general trend in first ionisation energies down a group?

Sharp decrease

Why is there a decrease in first ionisation energy between Mg and Cl?

Mg=>1s²2s²2p⁶3s²

Al=>1s²2s²2p⁶3s²3p¹

Al has an unpaired electron, in an orbital on its own, the 3p sub shell is also slightly higher energy then 3s sub shell, so experiences a lesser nuclear attraction. This means that it is easier to remove, so has a lower fires ionisation energy.

Why is there a decrease in first ionisation energy between P and S?

P - 3s(2e^-) 3p(e^-)(e^-)(e^-)

S - 3s(2e^-) 3p(2e^-)(e^-)(e^-)

S has an extra electron in a pair, so experiences repulsion, meaning that it requires less energy to remove, and has a lower first ionisationenergy