Atomic Orbitals & Ionisation Energy

Question 1

Define first Ionisation Energy

Answer 1

The energy required to remove one mole of electrons from one mole of an element in its gaseous state

Question 2

Ionisation energy general equation

Answer 2

X(g) –> X+(g) + e-

Question 3

Why does it require more energy for successive Ionisation Energies?

Answer 3

As electrons further from the nucleus are easier to remove, while those closest to the nucleus need most energy as they have the strongest nuclear attraction. More energy is needed as it is already a positive ion and electrons are closer to nucleus (more attraction)

Question 4

What does a large jump in Ionisation energy show?

Answer 4

Indicates that electrons are being removed from a new energy level that’s closer to the nucleus. The number of electrons in each group corresponds to the number in each energy level.

Question 5

Trend in Ionisation Energy down group 2

Answer 5

Down the group, nuclear charge increases, but it becomes easier to remove on electron. The outermost electrons are in energy levels that are further from the nucleus, Inner electrons shield outer electrons from the nucleus’ charge & allow the outermost electrons to be removed more easily.

Question 6

Anomalies in the trend of Ionisation energy across period 3?

Answer 6

1st IE for Al is less than Mg;
- Mg; [Ne] 3s2 - Al; [Ne] 3s2 3p1
– Though Al has a higher nuclear charge than Mg, the outermost electron is in a 3p orbital which is slightly further from the nucleus than the 3s orbital, so less energy needed to remove it.
1st IE between P and S
- P; [Ne] 3s2 3p3 -S; [Ne] 3s2 3p4
– In P, each 3p orbital electron occupies a different 3p orbital but in Sulphur, one of the 3p orbitals must have 2 electrons, so repulsion between the electron pair makes it easier to remove one of them despite an increase in nuclear charge.