C5.2. Bonding, Structure and the Properties of Matter

What are the three types of strong chemical bonding?

Ionic, covalent and metallic bonding.

What is ionic bonding?

The strong electrostatic attraction between oppositely charged ions.

What is covalent bonding?

The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms.

What is metallic bonding?

The strong electrostatic attraction between positive metal ions and delocalised electrons.

Which elements usually form ionic compounds?

Metals combined with non-metals.

Which elements usually form covalent bonds?

Non-metals.

Where does metallic bonding occur?

In metals and alloys.

What happens during ionic bonding?

Electrons are transferred from metal atoms to non-metal atoms.

What happens to a metal atom when it loses electrons?

It becomes a positively charged ion.

What happens to a non-metal atom when it gains electrons?

It becomes a negatively charged ion.

Why do atoms form ions?

To obtain a stable electronic structure, usually with a full outer shell.

What ion does a Group 1 metal form?

A +1 ion.

What ion does a Group 2 metal form?

A +2 ion.

What ion does a Group 6 non-metal form?

A −2 ion.

What ion does a Group 7 non-metal form?

A −1 ion.

What is a giant ionic lattice?

A regular structure containing oppositely charged ions held together by strong electrostatic forces in all directions.

Why do ionic compounds have high melting and boiling points?

There are strong electrostatic attractions between many oppositely charged ions, requiring lots of energy to overcome.

Why do solid ionic compounds not conduct electricity?

The ions are fixed in position and cannot move.

Why do molten ionic compounds conduct electricity?

The ions are free to move and carry electrical charge.

Why do ionic compounds dissolved in water conduct electricity?

The ions are free to move through the solution and carry electrical charge.

What should you be able to draw for ionic compounds?

Dot-and-cross diagrams showing electron transfer for compounds formed from Group 1 or 2 metals and Group 6 or 7 non-metals.

What is the charge of an ion formed by a Group 1 metal?

+1.

What is the charge of an ion formed by a Group 2 metal?

+2.

What is the charge of an ion formed by a Group 6 non-metal?

−2.

What is the charge of an ion formed by a Group 7 non-metal?

−1.

How can you work out the formula of an ionic compound?

Combine ions in ratios that give an overall charge of zero.

What is the empirical formula of an ionic compound?

The simplest whole-number ratio of the ions in the compound.

What is covalent bonding?

The sharing of pairs of electrons between atoms.

What is a covalent bond?

A shared pair of electrons with strong electrostatic attraction between the electrons and the nuclei of the bonded atoms.

What are small molecules?

Substances containing a small number of atoms joined by covalent bonds.

What are examples of substances made of small molecules?

Hydrogen, chlorine, oxygen, nitrogen, hydrogen chloride, water, ammonia and methane.

What should you be able to draw for covalent substances?

Dot-and-cross diagrams for hydrogen, chlorine, oxygen, nitrogen, hydrogen chloride, water, ammonia and methane.

What does a single line represent in a displayed covalent structure?

A single covalent bond, meaning one shared pair of electrons.

What is a giant covalent structure?

A structure in which very large numbers of atoms are joined by strong covalent bonds.

What are examples of giant covalent structures?

Diamond, graphite and silicon dioxide.

What are polymers?

Very large molecules made from many repeating units joined by strong covalent bonds.

What is a monomer?

A small molecule that joins with other monomers to form a polymer.

What is metallic bonding?

The strong electrostatic attraction between positive metal ions and delocalised electrons.

What does delocalised mean?

The electrons are not associated with one particular atom and can move through the whole structure.

What is the structure of a metal?

A giant structure of atoms arranged in a regular pattern, with delocalised outer-shell electrons.

What are the three states of matter?

Solid, liquid and gas.

What happens to particles in a solid?

They are closely packed and vibrate around fixed positions.

What happens to particles in a liquid?

They are close together but can move past each other.

What happens to particles in a gas?

They are far apart and move randomly.

What happens during melting?

A solid changes into a liquid at its melting point.

What happens during freezing?

A liquid changes into a solid at its freezing point.

What happens during boiling?

A liquid changes into a gas at its boiling point.

What happens during condensing?

A gas changes into a liquid.

What determines the amount of energy needed to change state?

The strength of the forces between the particles.

What happens when a substance with stronger forces between particles changes state?

More energy is needed.

What do the state symbols (s), (l), (g) and (aq) mean?

Solid, liquid, gas and aqueous solution respectively.

What is an aqueous solution?

A substance dissolved in water.

What is the structure of an ionic compound?

A giant ionic lattice containing oppositely charged ions.

Why do ionic compounds have high melting and boiling points?

Strong electrostatic forces act between oppositely charged ions throughout the giant lattice.

Why can ionic compounds conduct electricity when molten or dissolved but not when solid?

The ions can move when molten or dissolved but are fixed in position when solid.

What are the typical properties of small molecules?

They usually have low melting and boiling points and do not conduct electricity.

Why do small molecular substances have low melting and boiling points?

There are weak intermolecular forces between molecules, which require relatively little energy to overcome.

When a small molecular substance melts or boils, what bonds are overcome?

The weak intermolecular forces between molecules, not the strong covalent bonds within molecules.

What happens to intermolecular forces as the size of molecules increases?

They become stronger.

How does increasing molecular size affect melting and boiling points?

Larger molecules generally have higher melting and boiling points.

Why don't small molecular substances conduct electricity?

Their molecules have no overall electric charge and there are no free charged particles.

What is a polymer?

A substance made of very large molecules containing many repeating units.

What type of bonding exists within polymer molecules?

Strong covalent bonds.

Why are polymers generally solid at room temperature?

The intermolecular forces between their very large molecules are relatively strong.

What is a giant covalent structure?

A structure where all the atoms are linked by strong covalent bonds.

What are the properties of giant covalent structures?

They are solids with very high melting points.

Why do giant covalent structures have very high melting points?

Large amounts of energy are required to break the many strong covalent bonds.

What are the three giant covalent structures named in the AQA specification?

Diamond, graphite and silicon dioxide.

What is the structure of diamond?

Each carbon atom forms four covalent bonds with other carbon atoms in a giant structure.

Why is diamond very hard?

Each carbon atom is strongly bonded to four other carbon atoms throughout the giant structure.

Why does diamond have a very high melting point?

Many strong covalent bonds must be broken.

Why does diamond not conduct electricity?

It has no delocalised electrons or other free charged particles.

What is the structure of graphite?

Each carbon atom forms three covalent bonds with three other carbon atoms, creating layers of hexagonal rings.

What holds the layers of graphite together?

There are no covalent bonds between the layers.

Why is graphite soft?

The layers can slide over each other because there are no covalent bonds between them.

Why does graphite conduct electricity?

One electron from each carbon atom is delocalised and can move through the structure.

How is graphite similar to metals?

Both have delocalised electrons that can carry electrical charge.

What is graphene?

A single layer of graphite consisting of carbon atoms arranged in hexagonal rings.

What are fullerenes?

Molecules made from carbon atoms arranged in hollow shapes.

What are nanotubes?

Cylindrical fullerenes made from carbon atoms.

What are some uses of fullerenes?

They can be used for drug delivery and as lubricants.

What are some uses of nanotubes?

They can be used to reinforce materials and in electronics.

What are metals made of?

Giant structures of atoms with strong metallic bonding.

Why do most metals have high melting and boiling points?

Strong metallic bonds require a large amount of energy to overcome.

Why are pure metals malleable?

The layers of atoms can slide over each other while the metallic bonding remains.

What is an alloy?

A mixture of two or more elements, at least one of which is a metal.

Why are alloys harder than pure metals?

Different-sized atoms distort the regular layers, making it more difficult for the layers to slide.

Why are pure metals often too soft for many uses?

Their regular layers of atoms can slide over each other easily.

Why do metals conduct electricity?

Their delocalised electrons can move through the structure and carry electrical charge.

Why do metals conduct thermal energy?

Their delocalised electrons transfer energy through the metal.

How does the structure of a substance affect its properties?

The type of bonding and arrangement of particles determine properties such as melting point, hardness and electrical conductivity.