1.5 Solid Structures

Question 1

ionic solids

Answer 1

Ionic solids (crystals) are giant lattices of positive and negative ions. Structures are made of the same base unit repeated over and over again.
The structure of the crystal depends on the relative number of ions and their sizes.

Question 2

physical properties of ionic solids

Answer 2

High melting and boiling temperatures – It takes a large amount of energy to overcome the strong electrostatic forces between the oppositely charged ions.

• Often soluble in water – The oxygen end of the water molecules is attracted to the positive ions, and the hydrogen ends of the water molecules are attracted to the negative ions.
• Hard but brittle – When force is applied, layers of ions slide over each other causing ions of the same charge to be next to each other; the ions repel each other and the crystal shatters.
• Poor electrical conductivity when solid, but good when molten or dissolved – In the solid state, the ions are
  fixed in position by the strong ionic bonds; however, when molten or dissolved, the ions are free to move

Question 3

giant covalent structure

Answer 3

Giant covalent solids consist of networks of covalently bonded atoms arranged into giant lattices.

Question 4

structure of diamond

Answer 4

each carbon atom is joined to four others by strong covalent bonds. The atoms arrange themselves in a tetrahedral shape. This
makes it very hard

Question 5

properties of diamond

Answer 5

It has a very high melting point – a lot
of energy is needed to break the numerous strong covalent bonds.

It does not conduct electricity – there are no
free electrons or ions present.

Question 6

structure of graphite

Answer 6

Graphite consists of hexagonal layers. Each
carbon is joined to three others by strong
covalent bonds. The extra electrons are
delocalized within the layer. The layers are held together by weak van der Waals forces.

Question 7

properties of graphite

Answer 7

It has a very high melting temperature – it has
strong covalent bonds in the hexagon layers.

It is soft and slippery – the weak forces between
the layers are easily broken, so the layers can
slide over each other.

It is a good conductor of electricity – the delocalized electrons are free to
move along the layers so an electric current can flow

Question 8

simple molecular solids

Answer 8

These consist of covalently bonded molecules held together by weak intermolecular forces.

Question 9

properties of simple molecular solids

Answer 9

Low melting and boiling temperatures – Although the covalent bonds within the molecules are strong, the intermolecular forces holding the molecules together are weak and do not need much energy to break.

Poor conductors of electricity – They do not contain delocalized electrons or ions.

Question 10

examples of simple molecular solids

Answer 10

1. iodine
2. ice

Question 11

iodine (simple molecular)

Answer 11

In iodine, atoms are covalently bonded in pairs to form diatomic I2 molecules. These molecules are held together by weak van der Waals forces and are arranged in a regular
pattern.

Question 12

ice (simple molecular)

Answer 12

In ice, molecules of water are arranged in rings of six held together by hydrogen bonds. In this ordered structure, the water molecules are further apart than they are in the
liquid state. Since there are large areas of open space inside the rings, ice is less dense than liquid water at 0˚C

Question 13

metals

Answer 13

Metal atoms bond together to form a giant metallic structure.

Metals consist of a regular arrangement of positive ions(cation) in a lattice surrounded by a ‘sea’ of delocalized electrons. The strong metallic bond is due to the electrostatic forces of attraction between the nucleus of the cations and the delocalized electrons.

Question 14

properties of metallic structure

Answer 14

High melting temperatures – A large energy is needed to overcome the strong forces of attraction between the nuclei of the metal cations and the delocalized electrons; the melting temperature is affected by the number of delocalized electrons per cation and the size of the cation.

Hard – The metallic bond is very strong.
Good conductors of electricity both in the solid and molten state – The delocalized electrons can carry a current because, when a potential difference is applied across the ends of a metal, they will be attracted to and move
towards the positive terminal of the cell.

Good thermal conductors because the delocalized electrons can pass kinetic energy to each other.

Malleable (can be shaped) and ductile (can be drawn into a wire) – When a force is applied to a metal, the layers of cations can slide over each other; however, the delocalized electrons move with the cations and prevent forces of repulsion forming between the layers.