Physics GCSE 4.3 Particle Model of Matter and 4.4 Atomic Structure

Solids

Strong forces of attraction

Holds the particles close together in fixed position creating a regular lattice structure

Definite shape and structure

Can vibrate

When heated - they vibrate more and when the temperature hits that object’s melting point - the particles break free of their bonds - solid melts into a liquid

Liquids

Have weak forces of attraction between particles therefore are free to move

They are still compact therefore have a definite volume

Their shape can change therefore it can flow to fit a container

When heated, the particles gain more energy therefore move around faster. The bonds between particles weaken until the temperature hits the substance’s boiling point and the bonds break - turning the liquid to a gas

When liquid is cooled down, the particles won’t have enough energy to overcome the attracting between the molecules and even more bonds will form, keeping the particles in place to form a solid - Freezing

Gases

Forces of Attraction between different particles are very weak - free to move around by themselves

Don’t keep a definite shape or volume - Always fill a container

Gases are constantly moving with random motion (straight lines in any direction) - get deflected by solid walls and other particles

When heated, the particles get more energy and expand (in a expandable container like a balloon) or if the container is fixed, the pressure will increase

If gas is cooled down, the particles won’t have enough energy to overcome forces and bonds will start to form again between particles, condensing the gas into liquid

States of matter in a closed system

Changes in state won’t change the mass - still the same number of particles

Density of the substance will change - Solid (highest density), Gas (lowest density)

Density

Measure of how much mass a substance has, per unit of volume

Density (kg/m³)= mass (kg) /volume (m³)

How to find Density of Solids?

Mass: Place the solid a measuring scale to measure the mass

Volume:

• Regular Shape (cube) : Measuring length, width and height and multiplying together

• Irregular Shape: Eureka Can filled with water with an empty measuring cylinder under the outlet. The irregular shape can be placed in the eureka can and the volume of water exactly equal to that of the solid will flow out of the can into the measuring cylinder

Use equation to find Density

How to find Density of Liquids?

Mass: Empty measuring cylinder on balance and zero the balance. Then add liquid to measuring cylinder and record the mass of the volume of liquid

Volume: measured using measuring cylinder

Use equation to find density

The larger the volume, the more accurate the density: minimises the effects of uncertainty

Can also take multiple measurements to calculate a mean

Latent Heat

If a change of state happens:

The energy needed for a substance to change state is called latent heat. When a change of state occurs, the energy supplied changes the energy stored (internal energy) but not the temperature.

Specific Latent Heat (of vaporisation and fusion)

The specific latent heat of a substance is the amount of energy required to change the state of one kilogram of the substance with no change in temperature.

Cooling: Amount of energy released by change in state

Specific Latent heat of vaporisation: Energy change when a substance changes between a liquid and Gas

Specific Latent heat of Fusion: Energy change when a substance changes between a solid and liquid

Specific Latent Heat equation

E = ml

Energy (J) required or released = mass (kg) x Specific Latent Heat (J/kg)

Factors affecting Gas Pressure

• Temperature

• Concentration

• Volume

Factors affecting Gas pressure - Temperature

• When gas is heated up, the particles have more kinetic energy and therefore move around faster

• As they are moving around faster, there are more collisions with the walls of the container and each collision involves more force

• Therefore pressure increases with temperature

Factors affecting Gas pressure - Concentration

• Increasing the number of particles in a container but keeping the volume the same increases the concentration

• This increases the amount of collisions with the container wall and other particles

• Therefore pressure increases with concentration

Factors affecting Gas pressure - Volume

• Making the container smaller but keeping the number of particles the same increases the number of particles per unit of volume (higher concentration)

• More collisions

• As volume decreases, pressure increases

Flexible containers (balloon)

Changes in temperature and concentration changes the volume of the container rather than the pressure

Increase in the number and force of collisions will cause the balloon to expand

Pressure and Volume

Pressure and volume are inversely related

Pressure (Pascals) x Volume (m³)= constant value

pV = Constant OR p₁V₁ = p₂V₂

John Dalton’s discoveries

• Substances were made of atoms that were like tiny hard spheres 

• Each chemical element had its own atoms that differed in mass 

• Believed that they could not be divided or split

• In chemical reactions, atoms rearranged themselves and combined with other atoms in new ways

JJ Thomson’s Discoveries

• Discovered electron - tiny, negatively charged particle that was found to have a mass about 2000 times smaller than the lightest atom 

• Plum Pudding Model - Negatively charged electrons must be embedded in a cloud of positive charge

• Atoms don’t carry a charge so charges in atom must balance out 

Ernest Rutherford Discoveries

• Fired positively charged alpha particles at a thin sheet of gold 

• Some of the particles deflected to the side and some came back the way they were fired

• Rutherford Suggested Nuclear Model - Compact Nucleus with all the dense positively charged protons and negative charge existed as a cloud around the nucleus  

Niels Bohr Discoveries

• Noticed that light given out when atoms were heated only had specific amounts of energy

• Bohr proposed that electrons are orbiting nucleus in fixed energy levels or shells at set distances which prevent the atom from collapsing 

Energy is given out when electrons fall to a lower energy level

James Chadwick’s Discoveries

• Second subatomic particle proposed to explain missing mass in atoms 

Neutrons must have no charge but have the same mass as a proton