(1.44-1.51) covalent bonds + diagrams + properties

How is a covalent bond formed?

By atoms sharing a pair of electrons.

Define covalent bonds in terms of electrostatic attractions.

The electrostatic attraction between positive nuclei and negative shared pairs of electrons.

Which types of atoms does covalent bonding occur between?

Non-metal atoms

How is a dot-and-cross diagram drawn?

Draw circles for the outer shells of the atoms

Pair the electrons so that all atoms have full outer shells.

What is a simple molecular structure?

The term given to substances made up of covalently bonded molecules are held together through intermolecular forces.

Why are substances with simple molecular structures

gases/liquids

or solids with low melting/boiling points?

Although the atoms are covalently bonded,

the molecules are held together with weak intermolecular forces

which do not require as much energy to overcome,

resulting in easier melting/boiling.

Why do melting/boiling points of substances with simple molecular structures generally increase with increasing molecular mass?

Larger (more massive) molecules have stronger forces of attraction between them as there are more electrons.

Why do the majority of covalent structures not conduct electricity?

There are no charged, free to move particles- they are therefore generally insulators.

How many bonds can a carbon atom form?

4- four electrons in the outer shell and in Group 4

What is an allotrope?

Different structural modifications of an element.

Name three allotropes of carbon.

Diamond, graphite, buckminsterfullerene

What kind of structure is present in diamond?

A giant covalent structure

What is a giant covalent structure?

Atoms bonded to one another through strong covalent bonds, with no molecules or intermolecular forces.

Each carbon atoms forms bonds with 4 other carbon atoms, creating a tetrahedral structure.

Why does diamond have such a high boiling point?

In a giant covalent structure, strong covalent bonds between atoms need to be overcome to boil the substance. This takes a large amount of energy/heat.

Why is diamond so hard and dense?

Covalent bonds with atoms in a tetrahedral arrangement means that it is hard- although it is brittle.

Why is diamond not a conductor?

There are no free charged particles in the outer shell as they are all bonded with carbon atoms.

What is the structure of graphene?

Giant covalent structure wherein each carbon atom is bonded to three others.

What happens to the unbonded carbon atom in graphene?

It becomes part of a sea of delocalised electrons above and below each layer of carbon atoms.

Why is graphene a good electrical conductor?

Charged particles that are free to move (delocalised electrons)

What is the structure of graphite?

Made up of layers of covalently bonded carbon atoms (graphene) connected by weak intermolecular forces, surrounded by delocalised electrons.

Why does graphite have such a high sublimation point?

When boiling graphite, the strong covalent bonds between the carbon atoms need to be overcome, which requires high levels of energy.

Why is graphite slippery?

The layers are connected weakly so are easy to slip off. They are also it layers so can slide over each other.

Why is graphite a good conductor?

Many delocalised electrons means free to move, charged particles.

What is a fullerene?

A group of carbon allotropes that consist of molecules that form hollow tubes or spheres.

What is the structure of buckminsterfullerene?

A simple molecular structure with weak intermolecular forces. Each molecule is bonded with strong covalent bonds.

Why are buckyballs poor conductors?

No delocalised electrons to carry charge.