1: Ionisation Energy

Question 1

What is first ionisation energy?

Answer 1

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

Question 2

What state symbol must be used when writing ionisation energy half equations?

Answer 2

Gas

Question 3

How does a low ionisation energy affect the ability to form a positive ion?

Answer 3

The lower the ionisation energy, the easier it is to form a positive ion.

Question 4

What does a high ionisation energy mean for attraction between electrons and the nucleus?

Answer 4

A higher ionisation energy means that there is a stronger attraction between electrons and the nucleus, so more energy is required to weaken this attraction.

Question 5

Give 3 factors that can affect ionisation energy.

Answer 5

Nuclear charge.
Atomic radius.
Shielding.

Question 6

What does nuclear charge have to do with attraction towards electrons?

Answer 6

The higher the nuclear charge, the more protons in the nucleus, therefore the stronger the attraction for electrons.

Question 7

How does nuclear charge affect the size of atoms across the periodic table?

Answer 7

Across a period, atoms typically get
smaller (smaller atomic radius) due to a higher nuclear charge, leading to a stronger attraction between the nucleus and electrons, pulling the electron shells closer to the nucleus.

Question 8

If the atom has a larger atomic radius (increased distance between electrons and the nucleus) how will this affect ionisation energy?

Answer 8

The larger the atomic radius, the less attraction there is between the nucleus and outer electrons . This leads to a lower ionisation energy.

Question 9

What is shielding?

Answer 9

As the number of electrons between outer electrons and the nucleus increases, the outer electrons feel less attraction to the nucleus, as the inner shells block this.

Question 10

Define second ionisation energy.

Answer 10

The energy needed to remove an electron from each 1+ ion in 1 mole of 1+ ions to form 1 mole of gaseous 2+ ions.

Question 11

Why are second ionisation energies typically larger than first ionisation energies?

Answer 11

This is usually because the second electron is slightly closer to the nucleus. This means that there is stronger electrostatic attraction.

Question 12

What is successive ionisation energy?

Answer 12

Removing all electrons from an atom one by one until there are no electrons left in an atom.

Question 13

What have ionisation trends down group 2 provided evidence for?

Answer 13

The existence of electron shells.

Question 14

As you go down group 2, why does first ionisation energy decrease?

Answer 14

Atoms get larger. This means that the distance of the outer electron is further from the nucleus. There is also an increased shielding effect.

Question 15

Generally, as you go across a period, why does first ionisation energy increase?
Link this to nuclear charge and how it changes an atoms shape.

Answer 15

Increased nuclear charge means that the number of protons increases. This means that the charge of the nucleus is higher, leading to stronger attraction towards the electrons. This therefore means that size of the atom decreases as the higher charge pulls shells closer to the nucleus, meaning more energy is required to break this attraction.

Question 16

Explain the increase in first ionisation energy from Na to Mg in period 3, making reference to nuclear charge.

Answer 16

The magnesium atom has a higher nuclear charge than sodium as it has one more proton.

Question 17

Explain the drop in ionisation energy between Mg and Al in period 3, making reference to orbitals (atomic radius) and shielding.
What do these two effects override?

Answer 17

Aluminium’s outer electron is in the 3p orbital rather than the 3s compared to Mg. This means that the electron is further from the nucleus, so there is less attraction.
There is also additional shielding from the 3s shell.
Both of these factors override the effect of increased nuclear charge, leading to a drop in ionisation energy.

Question 18

Explain the drop in first ionisation energy between P and S, referring to electron repulsion.

Answer 18

In P, the electron is being removed from a singly occupied orbital , whereas sulfur’s outer electron is being removed from an orbital containing 2 electrons. Repulsion between 2 electrons in an orbital means that electrons are easier to remove from shared orbitals, as electrons are ‘unhappy’ in them.

Question 19

How can a successive ionisation graph tell you the period of an element?

Answer 19

There are large jumps in ionisation energy when a new shell is broken into. The number of outer electrons is equal to the period.