Periodicity

Question 1

What is periodicity?

Answer 1

The regular periodic variation of properties with atomic number and position in the Periodic Table

Question 2

What is thermal decomposition?

Answer 2

The breaking up of a chemical substance with heat into at least 2 chemical substances

Question 3

What is a displacement reaction?

Answer 3

A reaction in which a more reactive element displaces a less reactive element from an aqueous solution of the latter’s ions

Question 4

What is disproportionation?

Answer 4

Oxidation and reduction of the same element in a redox reaction

Question 5

What is the trend in first ionisation energy down a group?

Answer 5

It decreases

Question 6

What is the trend in first ionisation energy across a period?

Answer 6

It increases

Question 7

Explain the trend in first ionisation energy down a group

Answer 7

The outer electron is further away from the nucleus and is shielded by electrons in more inner shells so the electrostatic attraction to the nucleus decreases

Question 8

Explain the trend in first ionisation energy across a period

Answer 8

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

Question 9

What are the 2 exceptions to the general trend in first ionisation energy across a period

Answer 9

IE of group 3 is lower than group 2 as the outer electron is in a p-orbital which is higher in energy so evidence for sub-shells
IE of group 6 is lower than group 5 as the outer electron has paired up with another electron in a p-orbital so these repel each other and evidence for spin pairing in atomic orbitals

Question 10

What do the exceptions in the trend in first ionisation energy across a period support?

Answer 10

The Bohr model of the atom

Question 11

Give 3 examples of giant covalent lattices

Answer 11

Diamond
Graphite
Graphene

Question 12

Outline diamond

Answer 12

Tetrahedral structure
Poor electrical conductivity as no delocalised electrons as all outer shell electrons are used for covalent bonds
Hard as tetrahedral shape allows external forces to be spread throughout lattice

Question 13

Outline graphite

Answer 13

Strong hexagonal layer structure but weak van der Waals’ forces between layers
Good electrical conductivity as there are delocalised electrons between layers
Soft as bonding within each layer is strong but weak forces between layers allow layers to slide easily

Question 14

Outline graphene

Answer 14

Essentially a single layer of carbon in the from of graphite
Good electrical conductivity
Outstanding mechanical strength with respect to its thinness

Question 15

Name 5 points/properties of giant metallic lattices

Answer 15

1) Strong electrostatic attraction between cations and delocalised electrons
2) Can conduct electricity due to delocalised electrons even in solid state
3) High melting and boiling points as attraction strong as high temps are needed to break these bonds
4) Ductile (can be drawn or stretched) and malleable (can be hammered into shape)
5) This is because of delocalised electrons as they can move which allows atoms or layers to slide past each other

Question 16

Name 6 points/properties about giant covalent lattices

Answer 16

1) Strong covalent bonds between atoms
2) These bonds are throughout the structure
3) High melting and boiling as high temperatures needed to break strong covalent bonds
4) Cannot conduct electricity as no free charged particles except in graphite (and graphene) - electrons are localised
5) Insoluble in both polar and non-polar solvents because covalent bonds are too strong to be broken down by either polar or non-polar solvents
6) Silicon is a metalloid and has a limited number of delocalised electrons that can move through the structure, giving a low conductivity

Question 17

What type of bonding, structure and forces is present Group 1-3 (except Boron)?

Answer 17

Metallic, giant metallic and strong forces between cations and electrons

Question 18

What type of bonding, structure and forces is present Group 4?

Answer 18

Covalent, giant covalent and strong forces between atoms

Question 19

What type of bonding, structure and forces is present Group 5-8?

Answer 19

van der Waals’ forces, simple molecular and weak forces between molecules

Question 20

What happens between groups 1-4?

Answer 20

General increase in melting points as difference in ionic charge increases

Question 21

What happens between groups 4-5?

Answer 21

Sharp decrease in melting point as from giant structures to simple molecular and strong forces to weak intermolecular forces

Question 22

What happens between groups 5-8?

Answer 22

Comparatively low melting points