1.2 Periodicity

Question 1

Explain how the elements are arranged on the periodic table.

Answer 1

Elements in the periodic table are arranged in order of increasing atomic number. Elements in the same group have similar chemical properties because their atoms have the same number of electrons in their outer energy levels.

Question 2

Define covalent radius.

Answer 2

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

Question 3

Explain the trend in covalent radius across a period.

Answer 3

Across a period atomic size decreases.
Each subsequent atom has the same number of energy levels but one extra proton. This larger nuclear charge attracts the outermost electrons more strongly so ‘pulling’ them closer to the nucleus.

Question 4

Explain the trend in covalent radius down a group.

Answer 4

Down Group - atomic size increases. Each subsequent atom has one additional energy level of electrons than the previous atom so making the atom bigger.

Question 5

What is first ionisation energy?

Answer 5

First ionisation energy is the energy required to remove one mole of electrons from one mole of gaseous atoms.

Question 6

What is second ionisation energy?

Answer 6

Second ionisation energy is the energy required to remove one mole of electrons from one mole of gaseous 1+ ions.

Question 7

Explain the trend in ionisation energy across a period.

Answer 7

Across a period ionisation energy increases as each subsequent atom/ion has one additional proton so has a larger nuclear charge, so has a stronger attraction for the outermost electron, thus needing more energy to remove the outermost electron.

Question 8

Explain the trend in ionisation energy down a group.

Answer 8

Down a group, ionisation energy decreases as each subsequent atom/ion has one additional energy level of electrons, so the outermost electron is further from the nucleus, so is less strongly attracted to the nucleus. The outer electron is also more screened from the nuclear charge, so the attraction between the nucleus and outermost electron is less. This all leads to less energy being needed to remove the outermost electron.

Question 9

Define electronegativity.

Answer 9

Electronegativity is the strength of the attraction an atom involved in a covalent bond has for the shared pair of electrons in the bond.

Question 10

Explain the trend in electronegativity across a period.

Answer 10

Across a period electronegativity increases as each subsequent atom has greater nuclear charge so attracts the shared pair of electrons more strongly.

Question 11

Explain the trend in electronegativity down a group.

Answer 11

Down a group electronegativity decreases as each subsequent atom has one more level of electrons so the shared pair of electrons in the bond are further from the nucleus and are more screened from the positive charge of the nucleus so are less strongly attracted to the outermost electrons.

Question 12

Describe metallic bonding.

Answer 12

Metallic bonding is the electrostatic force of attraction between the positive metal ions and the negative delocalised electrons. It is a lattice structure.

Question 13

Name the metallically bonded elements of the first 20 elements of the periodic table.

Answer 13

Lithium, beryllium, sodium, magnesium, aluminium, potassium and calcium.

Question 14

Describe the structure of monatomic elements.

Answer 14

Monatomic elements exist as single atoms held together by London dispersion forces.

Question 15

Name the monatomic elements of the first 20 elements of the periodic table.

Answer 15

Helium, neon and argon.

Question 16

Describe the structure of covalent molecular elements.

Answer 16

Covalent molecular elements exist as molecules (atoms held together by covalent bonds). These molecules are held together by London dispersion forces.

Question 17

Name the covalent molecular elements of the first 20 elements of the periodic table.

Answer 17

H₂, N₂, O₂, F₂, Cl₂, P₄, S₈ (and fullerenes, e.g. C₆₀).

Question 18

Describe the structure of covalent network elements.

Answer 18

Covalent network elements exist as a giant network of atoms held together by covalent bonds. It is a lattice structure.

Question 19

Name the covalent network elements of the first 20 elements of the periodic table.

Answer 19

B, C (diamond, graphite) and Si.