Cemeg 1.2

Question 1

What is the ionisation energy across a period?

Answer 1

Ionisation energy increases across a period because the extra electron goes into the same shell and the electron is more strongly attracted by an increasing nuclear charge.

Question 2

What is the ionisation energy trend down a group?

Answer 2

Ionisation energy decreases on going down a group as there is greater shielding effect as the outer electrons are in higher electron shells or energy levels, which outweighs the greater nuclear charge.

Question 3

What is shielding effect?

Answer 3

The shielding effect is the decreasing attraction of the nucleus (nuclear charge) due to more inner complete electron shells.

Question 4

Why does helium have a higher 1st ionisation energy than hydrogen?

Answer 4

Helium has a greater nuclear charge than hydrogen but has no extra shielding.

Question 5

Explain why beryllium has a higher 1st ionisation energy than magnesium?

Answer 5

Beryllium has a higher 1st ionisation energy because Be has less shielding effect of the outer electron which outweighs the smaller nuclear charge.

Question 6

Explain why there is a large difference between the 1st and 2nd ionisation energies of potassium.

Answer 6

The 2nd electron is removed from an inner shell which is closer to the nucleus and has less shielding effect. After the 1st electron has been removed the effective nuclear charge is greater so the 2nd ionisation energy is much greater.

Question 7

Comparing one electron and a pair of electrons in an orbital.

Answer 7

Two electrons in the same orbital experience some repulsion from each other. This offsets the attraction of the nucleus, so that an electron is removed slightly easier from a paired orbital that expected.

Question 8

Explain why nitrogen has a higher 1st ionisation energy than oxygen.

Answer 8

The outer electron in oxygen is paired in an orbital whereas the outer electron for nitrogen is unpaired within the same shell. Since paired electrons in the same orbital experience some repulsion, it is easier to remove the outer electron of oxygen.

Question 9

ionisation energy __________ across a period

Answer 9

increases

Question 10

ionisation energy _________ on going down a group

Answer 10

decreases

Question 11

What causes the shielding effect?

Answer 11

More inner complete electron shells.

Question 12

__________ has a greater nuclear charge than __________

Answer 12

Helium, hydrogen