bonding

How are covalent bonds formed?

By atoms sharing electrons.

Which type of atoms form covalent bonds between them?

Non-metals.

Describe the structure and bonding of a giant covalent substance.

Billions of atoms bonded together by strong covalent bonds.

Describe the structure and bonding of small molecules.

Small numbers of atoms group into molecules with strong covalent bonds between atoms and weak intermolecular forces between molecules.

Describe the structure and bonding of polymers.

Many identical molecules joined by strong covalent bonds in a long chain, with weak intermolecular forces between the chains.

Why do giant covalent substances have high melting points?

It takes a lot of energy to break the strong covalent bonds between the atoms.

Why do small molecules have low melting points?

Only a small amount of energy is needed to break the weak intermolecular forces.

Why do large molecules have higher melting and boiling points than small molecules?

The intermolecular forces are stronger in large molecules.

Why do most covalent substances not conduct electricity?

They do not have delocalised electrons or ions.

Describe the structure and bonding in graphite.

Each carbon atom is bonded to three others in hexagonal rings arranged in layers – it has delocalised electrons and weak forces between the layers.

Why can graphite conduct electricity?

The delocalised electrons can move through the graphite.

Explain why graphite is soft.

Layers are not bonded so can slide over each other.

What is graphene?

One layer of graphite.

Give two properties of graphene.

Strong, conducts electricity.

What is a fullerene?

Hollow cage of carbon atoms arranged as a sphere or a tube.

What is a nanotube?

Hollow cylinder of carbon atoms.

Give two properties of nanotubes.

High tensile strength, conduct electricity.

Give three uses of fullerenes.

Lubricants, drug delivery (spheres), high-tech electronics.

What is an ion?

Atom that has lost or gained electrons.

Which kinds of elements form ionic bonds?

Metals and non-metals.

What charges do ions from Groups 1 and 2 form?

Group 1 forms 1+, Group 2 forms 2+.

What charges do ions from Groups 6 and 7 form?

Group 6 forms 2–, Group 7 forms 1–.

Name the force that holds oppositely charged ions together.

Electrostatic force of attraction.

Describe the structure of a giant ionic lattice.

Regular structure of alternating positive and negative ions, held together by the electrostatic force of attraction.

Why do ionic substances have high melting points?

Electrostatic force of attraction between positive and negative ions is strong and requires lots of energy to break.

Why don’t ionic substances conduct electricity when solid?

Ions are fixed in position so cannot move, and there are no delocalised electrons.

When can ionic substances conduct electricity?

When melted or dissolved.

Why do ionic substances conduct electricity when melted or dissolved?

Ions are free to move and carry charge.

Describe the structure of a pure metal.

Layers of positive metal ions surrounded by delocalised electrons.

Describe the bonding in a pure metal.

Strong electrostatic forces of attraction between metal ions and delocalised electrons.

What are four properties of pure metals?

Malleable, high melting/boiling points, good conductors of electricity, good conductors of thermal energy.

Explain why pure metals are malleable.

Layers can slide over each other easily.

Explain why metals have high melting and boiling points.

Electrostatic force of attraction between positive metal ions and delocalised electrons is strong and requires a lot of energy to break.

Why are metals good conductors of electricity and thermal energy?

Delocalised electrons are free to move through the metal.

What is an alloy?

Mixture of a metal with atoms of another element.

Explain why alloys are harder than pure metals.

Different sized atoms disturb the layers, preventing them from sliding over each other.

How big are nanoparticles?

1–100 nm.

How are nanomaterials different from bulk materials?

Nanomaterials have a much higher surface area-to-volume ratio.

What is the relationship between side length and surface area-to-volume ratio?

As side length decreases by a factor of ten, the surface-area-to-volume ratio increases by a factor of ten.

What are nanoparticles used for?

Used in healthcare, electronics, cosmetics, and catalysts.