Chapter 7 - The periodic table

Question 1

Explain the meaning of the term periodicity and give an example using the elements in period three

Answer 1

Periodicity is the gradual change in a property across a period that is repeated across each period. For example, the atomic radius of atoms across period three gradually falls.

Question 2

Briefly explain what is meant by ionisation energy

Answer 2

The ionisation energy is the energy required to remove an outer electron from the attractive force of the nucleus.

Question 3

What is the first ionisation energy?

Answer 3

The first ionisation energy is the energy required to remove an electron from each of one mole of gaseous atoms.

Question 4

Why does the first ionisation energy decrease down the group?

Answer 4

Further down the group the outer electron is further from the nucleus and shielded by electrons in more inner shells. The electrostatic attraction to the nucleus is reduced.

Question 5

Write an equation for the ionisation energy of chlorine

Answer 5

Cl(g) –> Cl+(g) + e-

Question 6

Explain whether chlorine or bromine has the lower first ionisation energy. (4 marks)

Answer 6

Bromine atoms are larger, so the outer electrons are further from the nucleus and shielded by more inner electrons. The electrostatic attraction between bromine’s outer electron and the nucleus is less, so the first ionisation energy is lower.

Question 7

Why does the first ionisation energy increase across period 2 and 3?

Answer 7

The number of protons in the nucleus increases, the outer electron is in the same shell with similar shielding. The electrostatic attraction of the outer electron to the nucleus increases.

Question 8

Why do Boron and Aluminium have lower first ionisation energies than Beryllium and magnesium? Which is an exception to the general trend.

Answer 8

The outer electrons of boron and aluminium are in a p orbital, higher in energy.

Question 9

Why does Oxygen and Sulphur have lower first ionisation energies than nitrogen and phosphorus - it’s an exception to the general trend.

Answer 9

The outer electrons of oxygen and sulphur have paired electrons in a p-orbital. These repel each other so one electron is more easily removed.

Question 10

What is the structure of the metallic elements?

Answer 10

The metallic elements have a giant metallic lattice structure.

Question 11

What is the structure of the non-metallic elements?

Answer 11

They have either a giant covalent lattice or are composed of simple molecules or atoms.

Question 12

Why is there strong bonding in metals such as lithium beryllium, sodium and magnesium.

Answer 12

There is strong electrostatic attraction between the cations (positive ions) and the delocalised electrons.

Question 13

What bonding is there in carbon and silicon?

Answer 13

Giant covalent lattice’s - The covalent bonds between the atoms are strong, these bonds are throughout the structure.

Question 14

What are the three structures of pure carbon?

Answer 14

Diamond graphite and graphene.

Question 15

What is the bonding like in simple molecules like oxygen, fluorine and nitrogen?

Answer 15

They are molecules with strong covalent bonds between atoms, but weak intermolecular forces between the molecules.

Question 16

What is bonding like in noble gases?

Answer 16

There are weak interatomic forces between the atoms

Question 17

Explain the boiling points in metals, carbon and silicon and other non-metals.

Answer 17

Metals have high boiling points due to the strong electrostatic attraction between the cations and delocalised electrons.
Carbon and silicon have high boiling points due to the strong covalent bonds that have to be broken.
The other non-metals have low boiling points due to weak intermolecular forces.

Question 18

Explain conductivity in in giant covalent structures

Answer 18

Giant covalent lattices are non-conductors of electricity, the only exceptions are graphene and graphite.

Question 19

Explain the solubility of metals

Answer 19

Metals do not dissolve.

Question 20

Explain the electrical conductivity of metals

Answer 20

Metals have delocalised electrons that can move so they are good conductors. Graphite and graphene are good conductors because they have delocalised electrons.

Question 21

Explain the solubility of giant covalent structures

Answer 21

Giant covalent lattices are insoluble in almost all solvents. The covalent bonds holding together the atoms in the lattice are far too strong to be broken by interaction with solvents.

Question 22

Explain why the general trend is that the first ionisation energy increases across period 2

Answer 22

The first ionisation energy increases across period 2 because each subsequent atom has one extra proton. The electron being removed is in the same shell so that shielding from inner electrons is similar. Overall, the electrostatic attraction of the outer electron to the nucleus is increased meaning that more energy is required.

Question 23

Explain why the first ionisation energy of oxygen is lower than that of nitrogen?

Answer 23

In nitrogen there are no paired electrons in the 2p orbitals. In oxygen, electrons are paired in one of the 2p orbitals. These electrons repel each other.