Particle Model of Matter Notes
GCSE Revision Notes
Density: The mass per unit volume of a material.
Density = mass ÷ volume
ρ=m÷V
If the mass is measured in grams and the volume in cm³, then the density will be in
g/cm³.
If the mass is measured in kg and volume in m³, then the density will
be in kg/m³.
The density of a material depends on what it is ma de of an d how its pa rticles a re a rrange d.
A dense material has its particles packed tightly togethe r. The pa rticles in a less dense
material are more spread out – if you compresse d the mate rial, its pa rticles woul d move
closer together, and it would become more dense.
Solids, liquids and gases:
The three states of matter are solid (e.g. ice), liqui d (e.g. wate r),
and gas (e.g. water vapour).
The particles of a substance in each state a re the same – only
the arrangement and energy of the particles are diffe rent.
SOLIDS: Strong forces of attraction hold the particles close togethe r in a
fixed, regular arrangement. The particles don’t have much ene rgy so
they can only vibrate about their fixed positions. The density is
generally highest in this state as the pa rticles a re closest togethe r.
LIQUIDS: There are weaker forces of attraction
between the particles. The particles are close togethe r, but can move past
each other, and form irregular arrangements. They have mo re ene rgy than
the particles in a solid – they move in random directions at low spee ds.
Liquids are generally less dense than solids.
GASES: There are almost no forces of attraction
between the particles. The particles have mo re
energy than in liquids and solids – they are f ree to
move, and travel in random directions at high speeds. Gases are gene rally
less dense than liquids – they have low densities.
Measuring Density Required Practical:
Solid object
1. Use a balance to measure its mass.
2. If it’s a regular solid (cube/sphere), start by measuring its
length, width and height with a rule r. Then calculate its volume
using the relevant formula for that shape.
3. For an irregular solid, you can find its volume by submerging it
in a eureka can filled with water. The water displaced by the
object will be transferred to the measuring cylinder.
1
, 4. Record the volume of water in the measu ring cylin de r – this is the volume of the object.
5. Use the formula mass / volume = density to calculate the density of the object.
Liquid
1. Place a measuring cylinder on a balance and zero the
balance.
2. Pour 10ml of the liquid into the measu ring cylin de r an d
record the liquid’s mass.
3. Pour another 10ml into the measuring cylin de r,
repeating the process until the cylinder is full an d
recording the total volume and mass each time.
4. For each measurement, use the formula to fin d the
density.
5. Finally, take an average of your calculate d densities. This
will give you a value for the density of the liqui d.
Changes of state:
The three states of matter are solid, liquid and gas.
The changes of state are melting, boiling, evapo rating an d soli difying, as well as sublimation
(solid gas) and deposition (gas solid).
When a substance changes state, the numbe r of molecules in that substance doesn’t change
and neither does its mass. The only thing that changes is its ene rgy.
Changes of state are physical changes, this means that you don’t en d up with a new
substance – it is the same substance you sta rte d with, just in a diffe rent fo rm.
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GCSE Revision Notes
Density: The mass per unit volume of a material.
Density = mass ÷ volume
ρ=m÷V
If the mass is measured in grams and the volume in cm³, then the density will be in
g/cm³.
If the mass is measured in kg and volume in m³, then the density will
be in kg/m³.
The density of a material depends on what it is ma de of an d how its pa rticles a re a rrange d.
A dense material has its particles packed tightly togethe r. The pa rticles in a less dense
material are more spread out – if you compresse d the mate rial, its pa rticles woul d move
closer together, and it would become more dense.
Solids, liquids and gases:
The three states of matter are solid (e.g. ice), liqui d (e.g. wate r),
and gas (e.g. water vapour).
The particles of a substance in each state a re the same – only
the arrangement and energy of the particles are diffe rent.
SOLIDS: Strong forces of attraction hold the particles close togethe r in a
fixed, regular arrangement. The particles don’t have much ene rgy so
they can only vibrate about their fixed positions. The density is
generally highest in this state as the pa rticles a re closest togethe r.
LIQUIDS: There are weaker forces of attraction
between the particles. The particles are close togethe r, but can move past
each other, and form irregular arrangements. They have mo re ene rgy than
the particles in a solid – they move in random directions at low spee ds.
Liquids are generally less dense than solids.
GASES: There are almost no forces of attraction
between the particles. The particles have mo re
energy than in liquids and solids – they are f ree to
move, and travel in random directions at high speeds. Gases are gene rally
less dense than liquids – they have low densities.
Measuring Density Required Practical:
Solid object
1. Use a balance to measure its mass.
2. If it’s a regular solid (cube/sphere), start by measuring its
length, width and height with a rule r. Then calculate its volume
using the relevant formula for that shape.
3. For an irregular solid, you can find its volume by submerging it
in a eureka can filled with water. The water displaced by the
object will be transferred to the measuring cylinder.
1
, 4. Record the volume of water in the measu ring cylin de r – this is the volume of the object.
5. Use the formula mass / volume = density to calculate the density of the object.
Liquid
1. Place a measuring cylinder on a balance and zero the
balance.
2. Pour 10ml of the liquid into the measu ring cylin de r an d
record the liquid’s mass.
3. Pour another 10ml into the measuring cylin de r,
repeating the process until the cylinder is full an d
recording the total volume and mass each time.
4. For each measurement, use the formula to fin d the
density.
5. Finally, take an average of your calculate d densities. This
will give you a value for the density of the liqui d.
Changes of state:
The three states of matter are solid, liquid and gas.
The changes of state are melting, boiling, evapo rating an d soli difying, as well as sublimation
(solid gas) and deposition (gas solid).
When a substance changes state, the numbe r of molecules in that substance doesn’t change
and neither does its mass. The only thing that changes is its ene rgy.
Changes of state are physical changes, this means that you don’t en d up with a new
substance – it is the same substance you sta rte d with, just in a diffe rent fo rm.
2
