C1 - Particles

There are strong forces of attraction between particles, which hold them in fixed positions in a very regular lattice arrangement The particles do not move from their positions, thus do not flow The particles vibrate about their positions - the hotter the solid becomes, the more they vibrate (causing them to expand slightly when heated) §

There is some force of attraction between the particles. They are free to move past each other, but they do tend to stick together Liquids 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 which causes them to expand slightly when heated.

There is next to no force of attraction between the particles - they are free to move They travel in straight lines and only interact when they collide Gases don’t keep a definite shape or volume and will always fill any container When particles bounce off the walls of a container, they exert a pressure on the walls 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

There is no space for the particles to move into

In the solid state, the particles vibrate around fixed positions and cannot move from place to place

A physical change happens when a substance changes state or shape, or breaks into pieces. No new substances are made and many can be reversed.

Freezing juice to make an ice lolly Mixing sand with water Dissolving sugar in water

A chemical change is a change that produces one or more new substances During the reaction, bonds between atoms break and the atoms change places - the reactants rearrange themselves to form different products. The properties of the new substances are often very different from the properties of the original substance Many chemical changes are difficult or impossible to reverse

Cooking eggs, cakes and other foods Steel rusting An acid reacting with an alkali to make a salt and water

Electrostatic forces of attraction

The forces between particles The size of particles The space between particles

He described atoms as solid spheres and said that different spheres made up the different elements

In 1897, J.J. Thomson concluded from his experiments that atoms were not solid spheres His measurements of charge and mass showed that an atom must contain even smaller, negatively charged particles - electrons He changed the ‘solid sphere’ idea into a new model known as the ‘plum pudding model’

In 1909, Rutherford and his students Geiger and Marsden, conducted the famous gold foil experiment. They fired positively charged alpha particles at an extremely thin sheet of gold

From the plum pudding model, they were expecting the particles to pass straight through the sheet, or be slightly deflected at most. Whilst most of the particles did go straight through, some were deflected more than expected and very few were deflected backwards.

He came up with the theory of the nuclear atom to explain his new evidence. There’s a tiny, positively charged nucleus at the centre, surrounded by a ‘cloud’ of negative electrons

Bohr suggested that electrons can only exist in fixed orbits or shells, and not anywhere in between. Each shell has a fixed energy.

The atom is made up of three subatomic particles: Protons Neutrons Electrons

Particle: Relative Mass: Relative Charge: Proton 1 +1 Neutron 1 0 Electron 0.0005 -1

The nucleus is in the middle of the atom It contains protons and neutrons It has a positive charge because of the protons Almost the whole mass of the atom is concentrated in the nucleus The nucleus has a radius of between 10^-15m to 10^-14m

Electrons move around the nucleus in electron shells (or orbitals) They are negatively charged They are very small, however their shells cover a lot of space The volume of their orbitals determines the size of the atom - atoms have a radius of about 10^-10m Electrons have virtually no mass and often taken as 0

The number of protons

They form when atoms (or groups of atoms) gain or lose electrons Negative ions form when atoms gain electrons - they have more electrons than protons Positive ions from when atoms lose electrons - they have more protons than electrons

Isotopes are different forms of the same element, which have the same number of protons but a different number of neutrons They have the same atomic number (number of protons), but different mass numbers (number of protons + neutrons)