Chemistry GCSE AQA: Chapter 3 - Structure and Bonding

Ionic bonding

• Particles are oppositely charged ions

• Occurs in compounds formed from metals combined with non-metals

Covalent bonding

• Particles are atoms which share pairs of electrons

• Occurs in most non-metallic elements and in compounds of non-metals

Metallic bonding

• Particles are atoms which share delocalised electrons

• Occurs in metallic elements and alloys

Electrons in ionic bonding

• Metal atoms lose electrons to become positively charged ions

• Non-metal atoms gain electrons to become negatively charged ions

• These oppositely charged ions are strongly attracted to one another by electrostatic forces

Groups of metals and non-metals in ionic bonding

• Metals in Groups 1 and 2

• Non-metals in Groups 6 and 7

Structure of ionic compounds

• A giant structure of ions (giant ionic lattice)

• Held together by strong electrostatic forces of attraction between oppositely charged ions

• The forces in the lattice act in every direction

Properties of ionic compounds

• High melting and boiling points - strong bonds between the ions which takes a lot of energy to overcome

• When solid, they cannot conduct electricity - ions are held in place

• When they are liquid (molten) or dissolved in water they carry electric current - ions are free to move

Electrons in covalent bonding

• Non-metal atoms (compound) share pair(s) of electrons to make covalent bonds - only in outer shell

• Held together by electrostatic forces of attraction between positively charged nuclei and shared pair of electrons

Examples of simple molecular substances

• Hydrogen (H2) - single covalent bond

• Chlorine (Cl2) - single covalent bond

• Oxygen (O2) - double covalent bond

• Nitrogen (N2) - triple bond

• Methane (CH4) - four covalent bonds

• Hydrogen Chloride (HCl) - single covalent bond

Properties of simple molecular substances

• Held together by strong covalent bonds but weak intermolecular forces

• Very low melting and boiling points - little energy required to break weak intermolecular forces (increase with size of the molecules)

• Don't conduct electricity - no free electrons or ions

Effect of increased molecule size

As molecule size increases:

• Strength of intermolecular forces increases

• More energy required to break them

• Melting/boiling point increases

Polymer

• Long chain of monomers (repeating units)

• Joined together by strong covalent bonds

• Strong intermolecular forces

Giant covalent structures (macromolecules)

• All atoms are bonded to each other by strong covalent bonds

• In a giant lattice structure

Properties of giant covalent structures

• High melting and boiling point - hard to overcome strong covalent bonds

• Non conductors of electricity, except graphite

Structure of diamond

• Each carbon atom is bonded to 4 other carbons (4 strong covalent bonds)

• Arranged in giant lattice

Properties of diamond

• Does not conduct electricity

• Very hard

• High melting / boiling point

• Insoluble in water

Uses of diamond

• Jewellery

• Cutting head in drills

Structure of graphite

• Arranged in layers of hexagonal rings (no covalent bonds between layers, only weak intermolecular forces)

• Each carbon atom joined to three other carbons (three covalent bonds)

• Each atom has one delocalised electron

Properties of graphite

• Conducts electricity (delocalised electrons free to carry charge throughout its structure)

• Soft (layers slide over each other)

Uses of graphite

• Pencils

• Electrolysis

• Lubricant

Structure of silicon dioxide

• Giant covalent structure

• Each silicon atom is covalently bonded to 4 oxygen atoms

• Each oxygen atom is covalently bonded with 2 silicon atoms

Properties of silicon dioxide

• Very hard

• High melting/boiling point

• Insoluble in water

• Does not conduct electricity

Structure of graphene

• One layer of graphite (one atom thick)

• Contains delocalised electrons

Properties of graphene

• Strong

• Light (can be added to composite materials to improve strength without adding much weight)

• Can conduct electricity

Uses of graphene

• Electronics and composites

Structure of fullerenes

• Carbon atoms arranged in hexagonal rings (can be with five or seven carbon atoms)

• Form hollow, cage-like molecules (e.g. C60)

Uses of fullerenes

• Delivering drugs to the body (can 'cage' other molecules by forming around another atom/molecule)

• Industrial catalysts (due to large surface area)

• Lubricants

Structure of buckminsterfullerene

• Hexagonal rings of carbon atoms

• 60 carbon atoms (C60)

• Spherical shape

Structure of nanotubes

• Hollow carbon cylinders formed from fullerenes

Properties of nanotubes

• High ratio between length and diameter of nanotube

• Can conduct both electricity and thermal energy

• High tensile strength (don't break when stretched)

Uses of nanotubes (nanotechnology)

• Electronics

• Strengthen materials without adding much weight

Advantage of 2D ball and stick model

• Shows which atoms are bonded to each other

Disadvantage of 2D ball and stick model

• Does not show true shape of the molecule

Advantage of 3D ball and stick model

• Shows the shape of a molecule

Disadvantage of 3D ball and stick model

• Does not show how it is bonded via electrons

Advantage of dot and cross diagram

• Shows electrons from each atom

Disadvantage of dot and cross diagram

• It is a 2D representation

Structure of metals

• Giant structure of positive ions

• Arranged in layers

• Sea of delocalised electrons

• Strong forces of electrostatic attraction between positive metal ions and negative electrons

Properties of metals

• High melting/boiling points (electrostatic forces require a lot of energy to break down)

• Good conductors of electricity and heat (delocalised electrons free to carry charge throughout the metal)

• Soft (layers of atoms able to slide over each other)

• Malleable

• Ductile

• Shiny

Factors affecting strength of forces of attraction of particles in a material

• Material (structure of the substance, type of bonding)

• Temperature

• Pressure

Particle theory

• Energy needed for a change of state depends on strength of forces between particles

• Stronger forces between particles mean higher melting/boiling points

Limitations of particle theory

• Model shows no forces between particles

• Particles shown as solid spheres

Particles in solids

• Strong forces of attractions between particles, holding them close together in fixed positions to form regular lattice arrangement

• Particles don't move from their positions - keep a defined shape and volume

• Particles vibrate about their positions - the hotter the solid becomes, the more they vibrate (slightly expand when heated)

Particles in liquids

• Weak force of attraction between particles

• Randomly arranged and free to move, but tend to stick closely together

• Have definite volume but not definite shape - will flow

• Constantly moving in random directions - the hotter the liquid gets, the faster they move (expand when heated)

Particles in gases

• Very weak force of attraction between particles

• Free to move and far apart

• Don't keep definite shape or volume - always fill space

• Move constantly with random motion - the hotter the gas gets, the faster they move (expand or pressure increases when heated)

State symbols

• solid (s)

• liquid (l)

• gas (g)

• aqueous (aq) - dissolved in water

Particles during melting (solid to liquid)

• Solid is heated and particles gain more KE

• Particles vibrate more, weakening the intermolecular forces holding the solid together

• At melting point, particles have enough energy to break free from their positions (temperature stays the same during this)

• Solid is now a liquid

Particles during boiling/evaporating (liquid to gas)

• Liquid is heated, the particles gain more KE

• Particles move faster, weakening and breaking bonds holding the liquid together

• At boiling point, particles have enough energy to break their bonds (temperature stays the same during this)

• Liquid is now a gas

Particles during condensation (gas to liquid)

• Gas cools, particles no longer have enough energy to overcome forces of attraction

• Bonds form between the particles

• At boiling point, many bonds have formed between particles

• Gas is now a liquid

Particles during freezing (liquid to solid)

• Liquid cools, particles have less KE so move around less

• Particles no longer have enough energy to overcome forces of attraction

• Bonds form between the particles

• At melting point, many bond have formed between particles so they are held in place

• Liquid is now a solid

Sublimation

• Solid to gas

Properties of nanoparticles

• Diameter between 1nm to 100nm

• Contain only few hundred atoms

• Large surface area to volume ratio

Uses of nanoparticles

• Catalysts (large SA:Vol ratio)

• Nanomedicine - could be used to deliver drugs (can be absorbed more easily by the body)

• Electronic circuits (can conduct electricity)

• Deodorants (silver nanoparticles have antibacterial properties)

• Sunscreens (better at protecting from harmful UV rays and provide better skin coverage)

Disadvantages of nanoparticles

• May have undiscovered side effects (possibly toxic)

• Unknown long-term impacts