2. Bonding, structure and the properties of matter

Types of strong bond

Ionic, covalent, and metallic bonds.

Particles for ionic bond

Ionic - ions.

Particles for covalent bond

Covalent - atoms.

Particles for metallic bond

Metallic - metal atoms and delocalised electrons.

Elements forming ionic bond

Ionic - metals and non-metals.

Elements forming covalent bond

Covalent - non-metals only.

Elements forming metallic bond

Metallic - metals only.

Bonding in a metal

A regular arrangement of positive metal ions surrounded by a sea of delocalised electrons.

Force holding metal together

Electrostatic attraction between positive ions and delocalised electrons.

Reason metals have high melting points

Strong electrostatic forces require a lot of energy to break.

Reason metals are good electrical conductors

Delocalised electrons can move and carry charge through the structure.

What is an alloy?

A mixture of a metal with other elements.

Properties of alloys compared to pure metals

Alloys are usually harder and less malleable.

Reason why alloys are harder

Different sized atoms distort the layers, making it harder for them to slide.

How an ionic bond forms

Electrons are transferred from a metal atom to a non-metal atom.

Direction electrons move in ionic bond

From the metal to the non-metal.

What is an ion?

A charged particle formed when atoms gain or lose electrons.

How to know how many electrons to move

Equal to the number needed to get a full outer shell.

How to determine number of each type of ion

The total positive and negative charges must balance.

Draw a lithium ion

A lithium atom with 2 electrons (Li⁺) and square brackets around it with a + charge.

Draw an oxide ion

An oxygen atom with 8 electrons (O²⁻) and square brackets around it with a 2− charge.

Name of overall structure made by an ionic compound

Giant ionic lattice.

Force holding an ionic compound together

Strong electrostatic attraction between oppositely charged ions.

Reason ionic compounds are solids at room temperature

They have high melting points due to strong forces between ions.

Formula of compound with two A ions and one B ion

A₂B.

Problem with dot and cross model of ionic bonding

It doesn't show the structure or scale of the lattice.

Problem with ball-and-stick model of ionic bonding

Bonds are shown as sticks, which don't exist in real ionic lattices.

Circumstances ionic compounds can conduct electricity

When molten or dissolved in water.

Reason ionic compounds conduct electricity when molten or dissolved

Ions are free to move and carry charge.

How a covalent bond forms

Atoms share pairs of electrons.

Small covalent molecule

Water (H₂O), carbon dioxide (CO₂), methane (CH₄), ammonia (NH₃), hydrogen (H₂), oxygen (O₂), nitrogen (N₂), chlorine (Cl₂).

Ways to draw small covalent molecules

Dot and cross diagrams; displayed formula.

Force holding small covalent molecules together in a solid

Weak intermolecular forces.

Boiling points of small covalent molecules

Low boiling points due to weak intermolecular forces.

Electrical conductivity of small covalent molecules

Do not conduct electricity as they have no free electrons or ions.

Polymer

A long chain molecule made from repeating units called monomers.

Monomer

A small molecule that can join together with others to form a polymer.

Bonds holding monomers together in a polymer

Covalent bonds.

Naming a polymer

Add 'poly' in front of the monomer name in brackets, e.g. poly(ethene).

Polymers at room temperature

They have large molecules with strong intermolecular forces.

Example of a polymer

A section of repeating units in a long chain, with bonds extending out of brackets.

Giant covalent structures

Diamond, graphite, silicon dioxide, graphene.

State of giant covalent structures

Solids.

Element in diamond and graphite

Carbon.

Bonding in diamond

Each atom bonded to 4 others in a rigid lattice.

Bonding in graphite

Each atom bonded to 3 others in layers.

Why diamond is hard

Strong covalent bonds in a rigid structure.

Why graphite is soft and slippery

Layers slide over each other due to weak forces between them.

Why graphite can conduct electricity

It has delocalised electrons that move between layers.

Graphene

A single layer of graphite, one atom thick.

Uses for graphene

Electronics and composite materials.

Fullerenes

Molecules of carbon shaped like tubes or spheres.

First fullerene discovered

Buckminsterfullerene (C₆₀).

Carbon nanotubes

Cylindrical fullerenes with very high strength and conductivity.

Uses for carbon nanotubes

Reinforcing materials, electronics, nanotechnology.

Size of nanoparticles

1-100 nanometres in size.

Size of fine and coarse particles

Fine: 100-2,500 nm; Coarse: 2,500-10,000 nm.

Other name for coarse particles

PM10 (Particulate Matter 10).

Properties of nanoparticles vs bulk materials

They have a very high surface area to volume ratio.

Uses for nanoparticles

Sunscreens, catalysts, drug delivery, electronics, antibacterial coatings, deodorants.