How bonding and structure are related to the properties of substances

Giant covalent molecules at room temperature

Solid

Why are they solid at room temperature

Millions of strong covalent bonds that take lots of energy to break

Giant covalent molecule 1: Diamond

Formed from carbon. Each carbon atom forms 4 covalent bonds to other carbon atoms. Very high melting and boiling points as large number of carbon atoms form large number of covalent bonds. Diamonds don’t conduct electricity because no free electrons

Giant covalent molecule 2: Silica/Silicon dioxide

Contains silicon and oxygen. Huge number of covalent bonds. Very high melting and boiling point.

Giant covalent molecules 3: Graphite

Made of carbon. High melting and boiling points. Soft and slippery, good conductor of electricity and heat. Each carbon atom form 3 covalent bonds that create hexagonal rings. Hexagonal rings arranged in layers. No covalent bonds between the layers, which makes it slippery.

Why is graphite a good conductor of heat?

Each carbon atom has one electron from outer shell that isn’t in covalent bond that can carry charge or thermal heat. They are delocalised electrons.

Solids

I extremely hard to compress as particles packed together with almost no spaces between them. Fixed shape, can’t flow. Particles vibrate but can’t move.

Liquids

Hard to compress, because particles are close together. Take shape of container, can flow as particles can move.

Gases

Easy to compress. Particles widely spaced. Gases spread out and fill the space of container because particles in gas move quickly and randomly

Melting

Solid to liquid, takes place at melting point. Energy put in to convert it to liquid. Energy required to break forces of attraction between particles in the solid. Once broken, particles can move around= liquid stat.

Liquid to solid

Freezing, takes place at same temperature as melting point.

Liquid to gas

Boiling. Takes place at boiling point.

Condensing

Gas to liquid. Same temperature as boiling point.

Limitations of simple particle model

Model assumes all particles are solid spheres, which is not true. Particles have many different shapes, not solid. It’s also assumed there are no forces between the particles, which isn’t correct.

Polymers

All molecule made up of smaller repeating units called monomers

Structure of polymers

Higher melting no boiling points than simple covalent structures but lower than large covalent structures. This is because although intermolecular forces are weak, there are many of them. Polymers are generally solids at room temperature.

2 main types of polymer

Addition polymers and condensation polymers

Graphene

Single layer of graphite= one atom thick. Excellent conductor of electricity because of delocalised electrons. Extremely strong, will be useful for new materials and electronics

Fullerenes

Molecules of carbon atoms with hollow shapes. Usually have hexagonal rings of carbon atoms but can have rings with five or seven carbon atoms.

Buckministerfullerene

C60. First fullerene discovered. 60 carbon atoms arranged in a hollow sphere. Carbon atoms form rings with either 6 carbon atoms or 5 carbon atoms.

Uses of fullerenes

1. Pharmaceutical deliveries

2. Lubricants

3. Catalysts

Carbon nanotubes

One group of fullerenes. Fullerenes shaped into long cylinders. Useful properties.

• High tensile strength (can be stretched a lot without breaking)

• Excellent conductors of heat and electricity

A use for carbon nanotubes

Reinforce materials. E.g, tennis rackets

Coarse particles (dust)

Many thousands of atoms. Diameter between 1x x10^-5 and 2.5 × 10^-6 metres.

Fine particles

Donated between 1 × 10^-7 and 2.5 × 10^-6 metres. Thousands of atoms

Nanoparticles

Diameter between 1-100 nanometres. Only a few hundred atoms.

As the particle decreases by 10

The surface area: volume ration increases 10x

Due to nanoparticles’ large surface area…

We need a much smaller quantity of nanoparticles than other particles to act as catalysts

Uses of nanoparticles

• Sun cream

• Medicine

• Cosmetics

• Catalysts

Risks of nanoparticles

It’s possible for nanoparticles to be absorbed into the body and enter cells. We don’t know consequences of this