Ionisation Energy Questions

Question 1

Define first ionisation energy

Answer 1

First ionisation energy is 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

Define successive ionisation energy

Answer 2

Successive ionisation energies are a measure of the energy required to remove each electron in turn

Question 3

Write an equation, including state symbols, for each of the following processes:
First ionisation of manganese

Answer 3

Mn(g) → Mn+(g) + e-

Question 4

Write an equation, including state symbols, for each of the following processes:
First ionisation of sulfur

Answer 4

S(g) → S+(g) + e-

Question 5

Write an equation, including state symbols, for each of the following processes:
Second ionisation of copper

Answer 5

Cu+(g) → Cu2+(g) + e-

Question 6

Write an equation, including state symbols, for each of the following processes:
Third ionisation of potassium

Answer 6

K2+(g) → K3+(g) + e-

Question 7

Write an equation, including state symbols, for each of the following processes:
Fifth ionisation of phosphorus

Answer 7

P4+(g) → P5+(g) + e-

Question 8

Give the electron configuration for the ion produced (above) in the first ionisation of sulfur

Answer 8

S+(g) has 15 electrons so is 1s22s22p63s23p3

Question 9

Give the electron configuration for the ion produced (above) in the fifth ionisation of phosphorus

Answer 9

P5+(g) has 10 electrons so is 1s22s22p6

Question 10

State and explain the trend in first ionisation energies as a Group is descended.

Answer 10

• First ionisation energy decreases as a Group is descended, because
Down a Group:
• The number of shells increases / so there is a bigger atomic radius;
• There is more shielding effect due to inner shell electrons;
• The increased shielding effect and increased distance of the outer electron from the nucleus far outweigh the increase in nuclear charge;
• So the nuclear attraction decreases down a Group, hence less energy is needed to remove the outer electron.

Question 11

State and explain how the first ionisation energy of fluorine compares to the first ionisation energy of carbon.

Answer 11

Fluorine has a higher first ionisation energy than Carbon, because
• F has (3) more protons / higher nuclear charge than C
• The outer electron fills the same shell in both F and C (hence same shielding)
• The nuclear attraction is higher in F (hence F has a smaller atomic radius).

Question 12

Explain why there is an increase in first ionisation energy between Na and Al.

Answer 12

• Al has (2) more protons / higher nuclear charge than Na
• The outer electron fills the same shell in both Na and Al (hence same shielding)
• The nuclear attraction is higher in Al (hence Al has a smaller atomic radius).

Question 13

Explain why there is a decrease in first ionisation energy between F and Na.

Answer 13

• Na has one more shell than F (cannot say atomic radius is bigger as given in question!)
• The outer electron in Na experiences more shielding than in F;
• The increased shielding effect (and distance) far outweigh the increase in nuclear charge in Na;
• So the nuclear attraction in Na is weaker than in F;
• So less energy is needed to remove the outer electron in Na (than in F).