ionisation energies

Question 1

What is the definition of first ionisation energy?

Answer 1

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

Question 2

What is the equation for the first ionisation energy?

Answer 2

X(g) –> X+ (g) + e-

Question 3

What is the general equation for ionisation energy?

What is n?

Answer 3

X(n-1)+ –> X(n)+ + e-

The number of ionisation energies

Question 4

Is ionisation energy in exothermic or endothermic process? Why?

Answer 4

endothermic - energy is required to overcome the attraction between the nucleus and the electron

Question 5

How does the number of ionisation energies affect how easy it is to form an ion?

Answer 5

The lower the ionisation energy, the easier it is to form an ion

Question 6

What are the three factors affecting ionisation energy?

Answer 6

1. Nuclear charge
2. Atomic radius or distance from the nucleus
3. Shielding

Question 7

How does the nuclear charge affect ionisation energy?

Answer 7

The higher the nuclear charge, the more protons there are in the nucleus, therefore the more positively charged nucleus is. If the nucleus is more positively charged it will attract electrons more strongly and therefore making it harder to remove.

Question 8

How does the atomic radius affect ionisation energy?

Answer 8

The more shells an element has, the further away an electron is to the nucleus. This means there is less forces of attraction between the nucleus and the electron meaning it is easier to remove

Question 9

How does the amount of shielding affect ionisation energy?

Answer 9

As the number of electrons between the outer electrons and the nucleus increases, the outer electrons feel less attraction towards the nucleus. The inner shells of electrons lessen the pull of the nucleus for the outer electrons therefore, the more shielding an element has, the harder it is for the electron to be removed.

Question 10

What does an element with a high ionisation energy mean?

Answer 10

There is a stronger attraction between the electron and the nucleus so more energy is needed to remove this electron

Question 11

What is the general trend in first ionisation energies down a group in the periodic table?
Why?
(3 things)

Answer 11

There is a general decrease in ionisation energy
This is because:
1. There is more shielding as there are more shells
2. The distance from the nucleus increases
3. The nuclear charge increases however the amount of shielding and atomic radius outweighs the increasing nuclear charge
Therefore it gets easier to remove and electron

Question 12

What is the general trend in first ionisation energies across a period in the periodic table?
Why?
(3 things)

Answer 12

There is a general increase in ionisation energy because:
1. The nuclear charge increases as there are more protons
2. The atoms get smaller so the atomic radius decreases
3. Shielding is the same
Therefore it gets harder to remove and electron

Question 13

In period 3, why does the ionisation energy decrease from magnesium to aluminium if there is a general increase in ionisation energy?

Answer 13

The outer electron in magnesium is an S sub shell. However, the outer electron in aluminium is in a p sub shell, so it is higher in energy than the outer electron in magnesium. This means the less energy is needed to remove it

Question 14

EXAM QUESTION:

Describe and explain the general trend of ionisation energy across period three

Answer 14

A general increase
- increased nuclear charge and more protons
- shielding remains the same
- atomic radius decreases
Anomalies - between Mg to Al
- The outer electron in magnesium is an S sub shell. However, the outer electron in aluminium is in a p sub shell, so it is higher in energy than the outer electron in magnesium. This means the less energy is needed to remove it

Question 15

How do you deduce which group it is from a set of ionisation energies?

Answer 15

From the set, find the largest jump from one element to another. Then subtract one from the number of the element
e.g. If the largest jump is between the second at third element, than the group number will be 2

Question 16

What is the second ionisation energy defined as?

Answer 16

The enthalpy change from the removal of one mole of electrons from one mole of gaseous 1+ cations to form one mole of gaseous 2+ cations at standard temperature and pressure

Question 17

What is the equation for the second ionisation energy?

Answer 17

X+ (g) –> X2+ (g) + e-

Question 18

What should you always include when writing in ionisation energy equation? (2 things)

Answer 18

1. State symbols

2. The corrects charge on the ion

Question 19

How does the first and successive ionisation energies in periods and groups give evidence for electron configuration in sub shells?

Answer 19

1. Within each shell, successive ionisation energies increase. This is because the electrons are being removed from an increasingly positive ion - there’s less repulsion amongst the remaining electrons so they held together more strongly by the nucleus
2. The big jumps in ionisation energy happen when a new shell is broken into - an electron is being removed from the shell closer to the nucleus