Bonding 2 - covalent & metallic

Question 1

What is covalent bonding?

Answer 1

The electrostatic attraction between the nuclei of two atoms and the bonding pair of electrons (shared between their outershells) which hold the two nuclei together

Question 2

The relationship between bond lengths and bond strengths for covalent bonds

Answer 2

Generally, shorter bond lengths are stronger bonds

Question 3

What is dative bonding

Answer 3

A dative covalent bond is a shared pair of electrons both from one donor atom. The other atom accepts the electron pair into a vacant orbital or is an electron deficient atom

Question 4

giant covalent structures: graphite

Bonding and properties

Answer 4

Graphite:
* Each carbon atom is bonded to 3 other carbon atoms
* This means each carbon atom has one electron free which is not localised

properties:
* Soft - Layers consist of the same sized atoms that are covalently bonded, but between layers are only weak intermolecular forces, meaning they can slide over eachother very easily
* Can conduct - Delocalised electrons are free to move between the layers, carrying charge (along sheets)

Question 5

giant covalent structures: diamond

Bonding and properties

Answer 5

Diamond:
* Each carbon atom is bonded to 4 other carbon atoms in a tetrahedral manner to form a giant molecule
* The bonds are covalent, and because the bonding electrons are close to the nucleus, they are very strong

properties:
* Very hard - 4 strong covalent bonds from each carbon in 3 dimensions
* Doesnt conduct - Electrons are held tightly between atoms
* Insoluble in water & organic solvents - no attractions that would outweigh the c-c bonds

Question 6

giant covalent structures: graphene

Bonding and properties

Answer 6

Graphene:
* A one atom thick sheet of graphite
* Can be rolled into a ball to form a fullerene, or into a cylinder to form a carbon nanotube
properties:
* Can conduct - Delocalised electrons are free to move between the layers, carrying charge (along sheets)

Question 7

Structures formed by covalently bonded substances

Answer 7

Two types of structures formed by covalently bonded subtances:
* Simple molecular (e.g. iodine and ice)
* Giant covalent lattice structures (e.g. diamond, graphite, graphene, silicon, silicon dioxide)

Question 8

Simple covalent structures/molecular lattices

Answer 8

Molecular solids:
* ice
* iodine

There are strong covalent bonds between the atoms in the molecules, and weaker intermolecular forces between the molecules. When heated it is these intermolecular foces that are broken.

Question 9

What is metallic bonding?

Answer 9

The strong electrostatic attraction between a lattice of positively charged ions and the ‘sea’ of delocalised electrons that surround them.

Question 10

Conductivity of metals (metallic bonding)

& how conductivity increases across a period

Answer 10

Metals are…
* Good electrical conductors - The sea of delocalised electrons allows charge to pass through the metal

Electrical conductivity increases Na –> Mg –> Al:
* The greater the charge on the positive ion, the stronger the attractive force as number of delocalised electrons increases
* Ions that are greater in size e.g. barium, produce a weaker attraction due to the greater atomic radius

Question 11

where are giant lattices present?

Answer 11

• ionic solids (giant ionic lattices)
• covalently bonded solids, such as diamond, graphite and silicon(IV) oxide (giant covalent lattices)
• solid metals (giant metallic lattices)