Unit 1 - Periodicity: Ionisation Energy & Electronegativity

Question 1

Ionisation Energy: First Ionisation Energy

Answer 1

The first ionisation energy is the energy required to remove one mole of electrons from one mole of gaseous atoms. Ionisation energy is measured in kJ mol-1.

E(g) –> E+(g) + e- (in data book)

Question 2

Ionisation Energy: First Ionisation Energy

Trends

Answer 2

The ionisation energy decreases down a group because
* the outermost electron is further from the nucleus so is easier to remove
* screening (shielding) from the nucleus by inner shells of electrons, making it easier to remove

In general, the ionisation energy increases across a period because
* the increased nuclear charge holds the outermost electron more strongly
* the atoms are smaller so the electron is closer to the nucleus

Question 3

Ionisation Energy: Second Ionisation Energy

Answer 3

The second ionisation energy is the energy required to remove a second mole of electrons.

E+(g) –> E2+(g) + e-

The second ionisation energy is larger than the first because the remaining electrons experience a greater attractive force from the nucleus. Therefore, more energy is needed to remove the second electron.

In some cases, there is a large increase in the second ionisation energy if the electon must be removed from a shell closer to the nucleus (full outer shell).

Question 4

Electronegativity

Answer 4

Atoms of different elements have different attractions for bonding electrons. Electronegativity is a measure of the attraction an atom involved in a bond has for the electrons of the bond. The higher the electronegativity, the greater the attraction for electrons.

Question 5

Electronegativity
Trends

Answer 5

Electronegativity increases across a period because the increased nuclear charge has a greater attraction for the bonding electrons.

Electronegativity decreases down a group because the bonding electrons are:
* further from the nucleus
* shielded (screened) from the nucleus by the inner shells of electrons