Bonding, structure and properties of matter

- Ions are charged particles - they can be single atoms or groups of atoms

- When atoms lose or gain electrons to form ions, all they want to do is get a full outer shell like a noble gas. Atoms with full outer shell are very stable

- When metals form ions they lose electrons from their outer shell to form pos ions

- When non-metals form ions, they gain electrons into their outer shells to form neg ions

- The number of electrons lost or gained is the same as the charge on the ion. E.g. If 2 electrons are lost the charge is 2+. If 3 electrons are gained the charge is 3- 

- The elements that most readily form ions are those in group 1, 2, 6 and 7

- Group one and two elements are metals and they lose electrons to form pos ions (cations)

- Group six and seven are non-metal and they gain electrons to form neg ions (anions)

- Elements in the same group all have the same number of outer electrons. So they have to lose or gain the same number to get a full outer shell, which means that they form ions with the same charge 

- A sodium atoms (Na) is in group one so it loses one electron to form a sodium ion

- In a polymer, lots of small units are linked together to form a long molecule that has repeating sections 

- All the atoms in a polymer are joined by strong covalent bonds

- Instead of drawing out a long polymer molecule which can contain thousands or even millions of atoms, you can draw the shortest repeating section, called the repeating unit

- To find the moleculer formula of a polymer, write down the molecular formula of a reapeating unit in brackets and put an 'n' outside 

- The intermolecular forces between polymer molecules are larger than between simple covalent molecules, so more energy is needed to break them. This means most polymers are solid at room temp

- The intermolecular forces are still weaker than ionic or covalent bonds, so they generally have lower bp than ionic or giant molecular compounds

- In giant covalent structures, all the atoms are bonded to each other by strong covalent bonds 

- They have very high melting and boiling points as lots of energy is needed to break the covalent bonds between the atoms

- They don't contain charged particles, so they don't conduct electricity - not even when molten (except for a few weird exceptions e.g. graphite)

- The main examples are diamond and graphite, which are both made from carbon atoms only, and silicon dioxide 

- Diamond is very hard

- Diamond has a giant covalent structure, made up of carbon atoms that each form four covalent bonds. 

- Those strong covalent structures take a lot of energy to break and give diamond a very high melting point

- It doesn't conduct electricity because it has no free electrons or ions

Graphite contains sheets of hexagons:

- In graphite, each carbon atom only forms three covalent bonds, creating sheets of carbon atoms arranged in hexagons

- These aren't any covalent bonds between the layers - they're only held together weakly, so they're free to move over each other. This makes graphite soft and slippery, so it's ideal as a lubricating material

- Graphite's got a high melting point - the covalent bonds in the layers needs lots of energy to break

- Only three out of each carbon's four outer electrons are used in bonds, so each carbon atom has one electron that's delocalised and can move. So graphite conducts electricity and thermal energy

Graphene is one layer of graphite:

- Graphene is a sheet of carbon atoms joined together in hexagons. The sheet is just one atom thick, making it a two-dimensional compound

- The network of covalent bonds makes it very strong, it's also incredibly light, so can be added to composite materials to improve their strength without adding much weight 

- Like graphite, it contains delocalised electrons so can conduct electricity though the whole structure. This means it has the potential to be used in electrons 

- Fullerenes are molecules of carbon, shaped like closed tubes or hollowed balls

- They're mainly made up of carbon atoms arranged in hexagons, but can also contain pentagons (rings of five carbon atoms) or heptagons (rings of seven carbon atoms)

- Fullerenes can be used to cage other molecules. The fullerene structure forms around another atom or molecule, which is then trapped inside. This could be used to deliver a drug into the body

- Fullerenes have a huge surface area, so they could help make great industrial catalysts - individual catalyst molecules could be attached to the fullerenes - they also make great lubricants 

- Fullerenes can form nanotubes  tiny carbon cylinders 

- The ratio between the length and diameter of nanotubes is very high

- They also have high tensile strength (don't break when stretched)

- Tech that uses very small particles such as nanotubes is called nanotechnology. Nanotubes can be used in electronics or to strenghten materials without adding to much weight, such as tennis racket frames 

- Metals also consist of a giant structure

- The electrons in the outer shell of the metal atoms are delocalised. These are strong forces of electrostatic attraction between the positive metal ions and the shared negative electrons 

- These forces of attraction hold the atoms together in a regular structure and are known as a metallic bonding. Metallic bonding is very strong

- Substances that are held together by metallic bonding include metallic elements and alloys

- It's the delocalised electrons in the metaliic bonds which produce all the properties of metals 

Most metals are solid at room temp

- The electrostatic forces between the metal atoms and the delocalised sea of electrons are very strong, so need lots of energy to be broken

- This means that most compounds with metallic bonds have very high melting and boiling points, so they're generally solid at room temp

- The delocalised electrons carry electrical current and thermal energy through the whole structure, so metals are good conductors of electricity and heat 

- The layers of atoms in a metal can slide over each other, making metals malleable - this means that they can be bent or hammered or rolled into flat sheets

- Pure metals often aren't quite right for certain jobs - they're often too soft when they're pure so are mixed with other metals to make them harder. Most of the metals we use everyday are alloys - a mixture of two or more metals or a metal and another element. Alloys are harder and so more useful than pure metals 

- Different elements have different sized atoms. So when another element is mixed with a pure metal, the new metal atoms will distort the layers of metal atoms, making it more difficult for them to slide over each other. This makes alloys harder than pure metals

- Materials come in 3 states - solid, liquid and gas. These are three states of matter. Which state something is at a certain temp depends on how strong the forces of attraction are between the particles of the material. How strong the forces are depends on three things:

- the material (structure of the substance and the type of bonds holding the particles together)

- the temp

- the pressure

You can use the model called particle theory to explain how the particles in a material behave in each of the three states of matter by considering each particle as a small, solid, inelastic sphere

Solids:

- In solids, there are strong forces of attraction between particles, which holds them close together in fixed positions to form a very regular lattice arrangement 

- The particles don't move from their positions, so all solids keep a definite shape and volume, and don't flow like liquids 

- The particles vibrate about their positions - the hotter the solid becomes the more they vibrate (causing solids to expand slightly when heated)

Liquids:

- In liquids, there's a weak force of attraction between the particles. They're randomly arranged and free to move past each other, but they tend to stick closely together

- Liquids have a definite volume but don't keep a definite shape, and will flow to fill the bottom of a container

- The particles are constantly moving with random motion. The hotter the liquid gets, the faster they move, this causes liquids to expand slightly when heated 

Gases:

- In gases, the force of attraction between the particles is very weak - they're free to move and are far apart. The particles in gases travel in straight lines

- Gases don't keep a definite shape or volume and will always fill any container 

- The particles move constantly with random motion. The hotter the gas gets, the faster they move. Gases either expand when heated, or their pressure increases 

Particle theory is a great model for explaining the three states of matter, but it isn't perfect. In reality, particles aren't solid or inelastic and they aren't spheres - they're atoms, ions or molecules. Also, the model does't show the forces the particles, so there's no way of knowing how strong they are 

State symbols tell you the state of the substance in an equation

(s) - state (l) - liquid (g) - gas (aq) - aquesous (dissolved in water)

Physical changes don't change particles - just their arrangement or their energy:

1) When a solid is heated, its particles gain more energy

2) This makes the particles vibrate more, which weakens the forces that hold the solid together

3) At a certain temp, called the melting point the particles have enough energy to break free from their positions. This is called melting and the solid turns into a liquid

4) When a liquid is heated, again the particles get even more energy

5) This energy makes the particles move faster, which weakens and breaks the bonds holding the liquid together

6) At a certain temp, called the boiling point, the particles have enough energy to break their bonds. This is the boiling (evaporating) The liquid becomes a gas 

7) As a gas cools, the particles no longer have enough energy to overcome the forces of attraction between them

8) Bonds form between the particles 

9) At the boiling point, so many bonds have formed between the gas particles that the gas becomes a liquid. This is called condensing 

10) When a liquid cools, the particles have less energy, so move around less

11) There's not enough energy to overcome the attraction between the particles, so more bonds form between them

12) At the melting point, so many bonds have formed between the particles that they're held in place. The liquid becomes a solid. This is freezing.

You might be asked to predict what state a substance is in at a certain temp. If the temp below the melting point of a substance it'll be a solid. If it's above the boiling point, it'll be gas. If it's in between 2 points, then it's a liquid