Unit 1-Periodicity

Question 1

What is meant by the covalent radius of an atom?

Answer 1

The covalent radius is a measure of the size of an atom.

Question 2

Explain the trend in covalent radius across a period

Answer 2

Increasing number of protons/nuclear charge pull electrons closer to nucleus reducing the covalent radius.

Question 3

Explain the trends in covalent radius down a group.

Answer 3

Atoms have more electron shells which cause an increase in shielding effect weakening the attraction for outer electrons and increasing the radius.

Question 4

What is meant by the ionisation energy of an atom?

Answer 4

The ionisation energy is the energy involved in removing one mole of electrons from one mole of gaseous atoms.

Question 5

Explain the trends in ionisation energy across a period.

Answer 5

Increasing number of protons/nuclear charge causes a greater attraction for outer electrons and therefore more energy is required to remove electrons. (ionisation energy increases)

Question 6

Explain the trends in ionisation energy down a group.

Answer 6

Atoms have more electron shells which cause an increase in shielding effect weakening the attraction for outer electrons and therefore less energy is required to remove electrons. (ionisation energy decreases)

Question 7

Magnesium has a 1^st ionisation energy of 738 kJ mol^-1

2^nd ionisation energy of 1451 kJ mol^-1

3^rd ionisation energy of 7733 kJ mol^-1

Explain this trend.

Answer 7

The third ionisation energy shows a massive increase because it requires an electron to be removed from an inner more tightly held shell.

Question 8

What is meant by an atom’s electronegativity?

Answer 8

Electronegativity is a measure of an atom’s attraction for bonding electrons.

Question 9

Explain the trend in electronegativity across a period.

Answer 9

Increasing number of protons/nuclear charge causes a greater attraction for bonding electrons (electronegativity increases)

Question 10

Explain the trend in electronegativity down a group.

Answer 10

Atoms have more electron shells which cause an increase in shielding effect weakening the attraction for bonding electrons (electronegativity decreases)

Question 11

The first 20 elements in the Periodic Table are categorised according to which four bonding and structures (hydrogen to calcium).
Give an example of each.

Answer 11

• metallic (Li, Be, Na, Mg, Al, K, Ca)
• covalent molecular (H₂, N₂, O₂, F₂, Cl₂, P₄, S₈ and fullerenes (eg C₆₀))
• covalent network (B, C (diamond, graphite), Si)
  
  • monatomic (noble gases)

Question 12

Describe bonding and structure in metallic elements.

Answer 12

Metallic bonding occurs between the atoms of metal elements. The outer electrons are delocalised (free to move).

This produces an electrostatic force of attraction between the positive metal ions and the negative delocalised electrons.

Question 13

Describe bonding and structure in covalent molecular elements.

Answer 13

Covalent molecules are small groups of atoms held together by strong covalent bonds inside the molecule and weak intermolecular forces between the molecules.

Examples (H₂, N₂, O₂, F₂, Cl₂, P₄, S₈ and fullerenes (eg C₆₀₎)

Question 14

Describe bonding and structure in covalent network elements.

Answer 14

Covalent networks are large, rigid three-dimensional arrangements of atoms held together by strong covalent bonds.

Question 15

Describe bonding and structure in monatomic elements.

Answer 15

Single, stable atoms.
Weak London dispersion forces.

Question 16

Compare the densities, melting point and electrical conductivity of elements which exists as:

1. Monatomic
2. covalent molecules
3. covalent networks
4. metallic lattices

Answer 16

1. Monatomic (noble gas) - low density, low melting point, non-conductor
2. Covalent molecular (N₂, P₄, S₈) - low density, low melting point, non-conductor
3. Covalent network - very high density, very high melting point, non-conductor (except graphite)
4. Metallic lattices (all metals) - high density, high melting point, conductor