Year 7 Science Revision Notes

Chemical Reactions Key Notes

Indicators + Acid & Alkali Hazards
Dilute laboratory acids and alkalis are irritants, which causes your skin to become
red or blistered
Strong acids and alkalis are corrosive as they can damage other materials by
wearing them away (destroying skin)!
An indicator is a special chemical that changes to a different colour in an acid or
alkali
The strength of an acid or alkali is measured by the pH scale – universal
indicator can tell you the pH of a solution as each colour has a separate pH value

Hazard symbols are used on bottles (and vehicles) that contain hazardous
chemicals – they can be identified by anyone, regardless of language



Neutralisation

The chemical reaction between an acid and alkali is called neutralisation

If you add just the right amount of acid and alkali together a neutral solution is
formed (the pH value gets close to pH 7 - neutral)

Acid + Alkali  Salt + Water

E.g. a bee sting is acidic, and can be neutralised with just the right amount of the
alkali bicarbonate of soda

A wasp sting is alkaline, and can be neutralised with just the right amount of the
acid vinegar

Chemical & Physical Changes

Chemical reactions happen anywhere that new substances are made

There are usually some obvious changes during a chemical reaction, including
 A change in colour
 A gas coming off (you may see fizzing or bubbling)
 A change in temperature (the reaction mixture may get hotter)
 A solid may be formed when two solutions are mixed together

Ice melting into water is an example of a physical change - no new substances
are formed during physical changes

Acid + Metal (Including H2 Test)
Many metals react with acids – producing the gas hydrogen
A burning splint is the test for this, producing a squeaky pop when it ignites
There are 3 tests we can do to find out what gas it is: -

 If it is carbon dioxide it will put out a lit splint / turn limewater cloudy when
it is bubbled through

 If it is oxygen, it will relight a glowing splint
 If it is hydrogen, it will ignite with a squeaky pop

Acid + Carbonates (Including CO2 Test)
When a metal carbonate reacts with acid, it fizzes and seems to disappear
The carbonate and the acid have reacted, producing a salt, water and carbon
dioxide

Metal carbonate + acid  salt + water + carbon dioxide
There are 3 tests we can do to find out what gas it is: -

 If it is carbon dioxide it will put out a lit splint / turn limewater cloudy when
it is bubbled through

 If it is oxygen, it will relight a glowing splint
 If it is hydrogen, it will ignite with a squeaky pop

Combustion
Combustion is the scientific name for burning
Combustion is the reaction when a substance burns and reacts with oxygen,
producing heat and light energy
Combustion results in the formation of both carbon dioxide & water
When substances burn, reacting with oxygen, the new products formed are
called oxides

Methane + Oxygen → Carbon Dioxide + Water
For a fire to take place there are three essential components: -

 Heat
 Oxygen
 Fuel

Explosives & Rusting
When a chemical releases a large amount of energy very quickly an explosion
occurs

An explosion is a chemical reaction, which causes huge amounts of gas to form
as well as releasing a lot of heat

The chemical reactions need oxygen to take place: -
 If the reaction needs oxygen from the air it is a combustion reaction
 If the reaction does not need additional oxygen from the air it is a
decomposition reaction

Rusting occurs when iron or steel is in contact with both water and oxygen

Rusting is a chemical reaction, which produced the reddish-brown iron oxide

We can prevent rusting by removing one of the requirements – i.e. remove the
water from contacting the iron (by painting it)

Cells & Reproduction Key Notes

Organs

A group of similar cells is called a tissue

A group of different tissues is called an organ

An organ is made from a group of different tissues, which all work together to do
a particular job

Both animals and plants have organs: -

Animals: -

 Heart
 Lung
 Stomach
 Brain
 Kidney
 Liver

Plants: -

 Leaf
 Root
 Stem
 Flower

Organs can work together do perform specific jobs – these are called organ
systems

The skeleton has three main functions: -
 Supporting the body
 Protecting some of the vital organs
 Helping the body move

Antagonistic muscles
Muscles work by getting shorter. We say that they contract, and the process is
called contraction.
Muscles are attached to bones by strong tendons. When a muscle contracts, it
pulls on the bone, and the bone can move if it is part of a joint.
Muscles can only pull and cannot push. This would be a problem if a joint was
controlled by just one muscle. As soon as the muscle had contracted and pulled
on a bone, that would be it, with no way to move the bone back again. The
problem is solved by having muscles in pairs, called antagonistic muscles.
Biceps and triceps
The elbow joint lets our forearm move up or down. It is controlled by two
muscles, the biceps on the front of the upper arm, and the triceps on the back
of the upper arm. The biceps and the triceps are antagonistic muscles.

 when the biceps muscle contracts, the forearm moves up

 when the triceps muscle contracts, the forearm moves down.

This solves the problem. To lift the forearm, the biceps contracts and the triceps
relaxes. To lower the forearm

Cells

A cell is the basic building block for both animals and plants

Cells are extremely small (we need a microscope to see them)

Animal cells contain: -

Part Function

Nucleus Controls what happens in the cell (but it is not a
‘brain’)!

Cell Membrane Controls what substances can enter and exit the cell

Cytoplasm Where chemical reactions take place (jelly-like
substance)

Plant cells contain (as well as the parts found in an animal cell): -

Part Function

Chloroplasts Where photosynthesis occurs (contain chlorophyll (which is
Vacuole green))
Cell wall
Contains cell sap (a solution of sugar and salt) helping with
rigidity
Made of cellulose, which gives support to the cell

Many organisms are multi-cellular - they are made up of lots of cells, not just one!
Many of these cells are specialised, sharing out the life processes (they work
together as a team, supporting the organism)
Animal specialisation – red blood cell (large surface area to carry oxygen); nerve
cell (long and can carry electrical signals); male sex cell (sperm with long tail for
movement); female sex cell (large cytoplasm as energy store)
Plant specialisation – root hair cell (large surface area to absorb water and
minerals); leaf cell (lots of chloroplasts to aid photosynthesis)

Specialised animal cells (red blood cell; nerve cell; egg cell; sperm cell): -

Specialised plant cells (root hair cell; leaf cell): -

Microscopes
A microscope makes things appear much bigger than they actually are – they
magnify them

This means we can view objects which are too small to be seen using the naked
eye

1. Place the smallest objective lens (the smallest lens) over the hole in the
stage

2. Turn the coarse focusing wheel to make the gap between the stage and
the objective lens as small as possible

3. Place a slide on the stage, and secure with the clips. The slide contains
what you want to see (your specimen)

4. Adjust the light source so light goes up through the stage
5. Look into the eyepiece lens
6. Turn the coarse focusing wheel slowing, until your specimen is in focus
7. To see your specimen in more detail, turn the next largest objective lens

over your specimen
8. Use the fine focusing wheel to get your image into focus again - do not

use the coarse focusing wheel - this can break your slide!
A specimen is the object we look at under a microscope. The specimen needs to
be thin, so light can pass through it
We use a coverslip between the slide and specimen which helps flatten it out. It
also helps keep the specimen in place, and stops it drying out

Magnification = magnification eyepiece lens x magnification objective lens

Ecology & Classification Key Notes

Habitats, Environmental Factors & Sampling Techniques
Habitat – the place where an organism lives
Environment – the conditions within the habitat
Different habitats can have some very different environments (conditions in the
habitat). The main factors are: -
 Amount of light / light intensity
 Amount of water (fresh / salt)
 Temperature
 Oxygen levels
 Nutrients
 Shelter
Different habitats are able to support different organisms, however plants and
animals develop features to adapt to their environment – they become better
suited to the conditions

Polar bears live in the Arctic, which is very cold. Adaptations of a polar bear
include: -
 Black skin to absorb heat well
 White appearance to camouflage it against the snow and ice
 Thick layers of fat and fur for insulation
 Wide feet with hair on their soles to avoid slipping

Camels live in deserts, which are hot and dry during the day but cold at night.
Adaptations of a camel include: -
 They can go for a long time without water (fat stored in hump)
 Slit-like nostrils and two rows of eyelashes to help keep the sand out
 Wide, flat feet to help them walk on the sand
 Thick fur to keep the sun off their skin (+ keep warm at night)

Cactuses live in deserts, which are hot and dry during the day but cold at night
with <25mm rainfall per year. Adaptations of a cactus include: -
 No leaves and small surface area (reduces water loss)
 Thick stem to store water
 Spines to stop herbivores eating them
 Shallow but extensive roots to absorb water as quickly as possible

Biologists often want to find out what organisms are present in an environment /
what these organism do /where these organisms go etc…
Often it isn’t feasible to identify all the organisms present, so instead samples
can be taken
Samples look at a small section, allowing us to predict what the whole is like –
e.g. would couldn’t feasibly measure the height of every blade of grass, but we
could look at a small sample grass and get an idea of what all the rest may be
like : -

 Tagging – e.g. a few whales can be tagged and tracked, to give us an idea of
where their migration routes are

 Pitfall traps – e.g. a small trap can be set to collect a range of organisms
within an area

 Quadrat – e.g. a quadrat is thrown in an area, and the number of organisms
within the quadrant are counted to give an estimate for a much larger area

A quadrat is a 1m2 sampling square

A quadrat is randomly placed in different locations, and the organisms within the
quadrat are counted so an average can be taken (the more samples, the more
accurate this method is)

Quadrats are usually used for plants, but they can also be used to estimate some
animal population sizes (as long as these only move a little)!

Adaptation & Predators & Prey

Many habitats do not stay the same all the time: -
 Daily changes to the environment include: -
 Changes in the amount of light (between day and night)
 Changes in the temperature
 Changes in the amount of water (i.e. rainfall / tidal variations)

Seasonal changes to the environment include: -
 Changes in temperature between the seasons (warm in summer, cold in

winter)
 Changes in the amount of light (between long daylight hours in the summer to

shorter days in the winter)
 Changes in vegetation due to conditions (lots of vegetation in summer, to

bare trees and snow-covered grown in winter)

Daily change: -
 Most flowers open their petals during the day (for pollination), but close them

at night for protection
 Some animals avoid predation by being nocturnal (come out at night) –

however some predators specialise at hunting during the night!
 Factors such as the tide (in or out) also affect the distribution of organisms

Seasonal change: -
 Some organisms hibernate during the cold winter months when food is scarce
 Different sized coats are grown by animals, e.g. a summer and winter coat
 Insects spend the winter as pupae
 Animals store food during plentiful times in preparation for when food

becomes scarce
 Some organisms migrate
 Flowers die off in winter as there are fewer birds or insects to pollinate tem
 Deciduous leaves lose their leaves (in case of permafrost)

Hibernation occurs in some organisms, whereby they slow their body functions
(e.g. breathing; metabolism; heart rate). This saves the organism a great deal of
energy (but they must store a great amount of energy during the summer when
food is plentiful), e.g. bats; tortoises; hedgehogs. *Bears are not true hibernators,
they only slow down (slow heart rate) but their body temperature remains the
same.

A predator is an animal which eats other animals for food, e.g. sharks, man,
tigers, lions, hawks, crocodiles, trap-door spiders etc…

Prey is the animal which gets eaten by the predator, e.g. seals, chicken,
antelope, zebra, buffalo, mice, beetles etc…

Food Chains / Webs & Pyramids Of Number / Biomass
A food chain shows what is eaten by what – each arrow means ‘eaten by’

E.g. rabbit  fox means the rabbit is eaten by the fox
Energy is transferred from one organism to another, in the direction of the arrow.
Food chains are never very long (usually only 4/5 stages at most) – why is this?

The arrow shows the energy being transferred from one organism to the next -
between each step energy is lost in a variety of ways, including: -
 Growth of the organism
 Reproductive costs
 Lost through waste products (poo)
 Lost through heat

This is why food chains are never that long - as lots of energy is lost from one
stage to the next

In most habitats organisms normally eat / are eaten by more than one other
organism. To represent this we use food webs (like food chains but they interlink
with one another), e.g. a pond

Producer - utilise the sun’s energy to produce their own food, e.g. plants and
algae

Consumer - organisms that require eating other organisms for their energy
supply. These can be primary consumers which eat the producers; secondary
consumers which eat the primary consumers; or tertiary consumers which eat the
secondary consumers etc…

Carnivore - an organism that eats other consumers, e.g. lion

Herbivore - an organism that eats other producers (plants), e.g. cow

Omnivore - an organism that eats both producers and consumers, e.g. human

The population of each organism in a food chain can be shown in a sort of bar
chart called a pyramid of numbers. The more organisms there are, the wider the

bar. The producer in the food chain always goes at the bottom of the pyramid of
numbers
E.g. clover  snail  thrush  hawk

Pyramids of number show how many organisms there are in a habitat
A pyramid of number for the food chain below might look like this: -

However they may not always look like classical pyramids: -

Biomass means the amount of biological material
The pyramid shows the amount of biological material at each level

*All food chains require light from the Sun – producers convert this light energy
into food via photosynthesis
Taxonomy
Many organisms share common features, which allow them to be grouped based
on these features – this is classification
The classification system begins with very big groups (lots of organisms) and
moves down into smaller groups (fewer organisms)
The biggest groups are called the kingdoms, of which there are 5

Animals are grouped into invertebrates (no backbone) and vertebrates (with a
backbone). The vertebrates are then sub-divided into 5 classes: -

Invertebrates: -

*You will not be expected to know all of the above
Keys are used to identify creatures – it involves a series of questions which have
two possible answers
The two answers divide the group into two parts (leading onto further questions)

Inherited & Environmental Variation

Offspring get half of their inherited features from each parent

During fertilisation, the nucleus from the sperm cell joins with the nucleus in the
egg cell, and a new nucleus is formed with all the genetic information needed

Some variations are inherited, whilst other variations are due to environmental
factors

Inherited variation is a characteristic you have got from your parents: -
 Gender
 Eye colour
 Hair colour
 Skin colour
 Lobed or lobeless ears

Offspring are similar, but not identical to their parents

During fertilisation ½ the genes are transferred from the male (sperm), and ½
from the female (egg)

This is why you inherit characteristics from both your mum and your dad (½ from
each)

Likewise, your siblings (brothers and sisters) also have ½ the genes of your
mum, and ½ of your dad (but your are not identical to them because the genes
can mix slightly)

Thousands of genes make up a living organism, and these can sometimes come
in different forms - e.g. a gene for blue eyes, and a gene for brown eyes. This is
why your parents may both have one eye colour, but you might have another

Variation in a feature as a result of the surroundings, is called environmental
variation, for example: -
 Hair length
 Language
 Weight
 Tattoos
 Scars

Characteristics of animals and plants can be affected by factors such as climate,
diet, accidents, culture and lifestyle

If you eat too much you will become heavier, and if you eat too little you will
become lighter

A plant in the shade of a big tree will not be able to photosynthesise as quickly as
one in the sunshine, so it will be smaller.

Energy Key Notes

Fuels & How Humans Obtain Fuel

Fuels are substances that release energy when they burn

Some fuels are better than others - e.g. one fuel may be easier to store, give off
more heat and pollute less

Energy is the ability to ‘do some work’ - everything that happens needs energy
(e.g. heating; cooking; lighting; movement of vehicles; and keeping us alive)!

A fuel is something that can release energy, making it useful for us to ‘do some
work’ such as moving a car; running across a field; heating a room; sending a
rocket into space…

Energy can be in many different forms, such as light, heat, sound, electrical,
kinetic (movement), nuclear etc…
Food is required by the body, along with oxygen, so that cells can respire.
Respiration occurs in every cell – it is the process of releasing energy. Every cell
in our body respires, converting this food (glucose) into energy (needed for
growth; repair; movement etc…)

Different foods have different amounts of energy in them – this is measured in
kilojoules (kJ) and calories (cal). This information is shown on the labels of foods,
as well as showing you what is contained within them

 Fat
 Carbohydrates (sugar / starch levels)
 Protein
 Vitamins
 Minerals
 Fibre
 Water

Fossil Fuels

The fossil fuels are coal; natural gas; and oil

They formed millions of years ago from the remains of living things

Coal was formed from plants, and oil and natural gas from sea creatures. When
the living things died, they were gradually buried by layers of rock

The buried remains were put under pressure and chemical reactions heated
them up, gradually changing into fossil fuels

Coal is used in power stations and to heat some homes

Natural gas is the gas we use for cooking and heating, and in Bunsen burners at
school

Crude oil is separated into lots of different substances at oil refineries, including
camping gas, petrol, diesel and kerosene (jet fuel)

Energy Origins (Renewable & Non-renewable)

Fossil fuels are non-renewable energy resources - once they have all been used
up they cannot be replaced

Renewable energy resources can be replaced, never running out

Energy can be transferred from many different resources - in non-renewable
resources such as fossil fuels, energy is stored chemically in the fuel, and
burning them releases this energy

Energy can also be transferred from renewable resources, such as solar cells,
where energy is absorbed from sunlight and turned into electricity

Nearly all the energy we use originally came from the Sun

Heat and light from the Sun provide us with energy directly

Plants also store the Sun’s energy through photosynthesis (utilising light to make
sugar from carbon dioxide and water)

Coal, oil and natural gas were formed from the remains of dead plants and
animals (the energy in these fuels came from the bodies of the plants and
animals)

The animals got their energy from the plants they ate, and the plants got their
energy from the Sun!

Solar power utilises sunlight directly

Wind is caused by the Sun heating up the Earth (convection currents)

Waves are caused by the build up of this wind

Hydroelectric power relies on water movement (which fell as rain after being
evaporated by the Sun’s energy)

*Only tidal energy (caused by the Sun and Moon’s gravity); nuclear energy
(energy stored within uranium); and geothermal energy (heat from the Earth) do
not originate in the Sun!

Forces & The Solar System Key Notes

Forces
A force is a push or a pull on an object

Contact forces - two objects in contact with each other
Non-contact forces - a force that acts over a distance

Types of force: -
 Gravitational Force - acting straight downwards
 Magnetic Force - push / pull exerted by a magnet
 Electrical Force - a force between two charged objects
 Reaction Force - force from the surface, usually acting straight upwards
 Contact Force (push / pull forces) - force which results in the object speeding

up, for example, due to an engine / rocket
 Friction - friction between surfaces slowing an object down. This can include

air resistance - (special type of frictional force) where air in the atmosphere
slows down a moving object
 Tension Force - pulling of a rope / cable from opposite ends
 Elastic Force - compression / extension of a spring or elastic product

We represent forces using arrows - the arrow points the way the force is working
The arrow also represents the size of the force - the bigger the arrow, the
greater the force is - these arrows always come in pairs…

Speed is a measurement of how quickly something is traveling at, which can be
in m/s; km/h; mph; cm/year etc…
Friction is a force which occurs when two objects interact

If an object has no force propelling it, it will slow down and eventually stop due to
friction. Friction occurs between solid surfaces which are gripping / sliding past
each other (e.g. a tyre on the road / marble down a ramp)
Resistance (drag) from the air or liquid - as you move air or liquid particles collide
into you (this is why a parachute slows you down and to go very fast cars need to
become streamlined)
Friction increases as speed increases - more speed = more air particles colliding
into you

Why Things Float
The reason some objects float and others sink is due to density
Density is an equation of an object’s mass divided by its volume

Density = mass / volume
If an object is more dense than water, it sinks
If it is less dense, it floats!
Objects will either sink of float, depending upon their density - if they are more
dense than water, they sink, less dense, and they float
The shape of an object has a lot to do whether it sinks or not - 100kg of steel will
sink, but 100kg of steel shaped into a boat will float, because overall the volume
of the boat is much bigger (it contains a great deal of space which isn’t steel), so
its overall density is reduced
*Buoyancy defined: an object in a fluid experiences an upward force equal to the
weight of the fluid displaced by the object – if the boat can displace a greater
mass of liquid than its own mass, then it will float!

Mass, Weight & Space
Mass is the amount of stuff there is (in kg)
Weight is caused by the pull of gravity (in N/kg) - this will be different if you are
own the Earth / Moon / in a black hole!

There are 9 planets in our solar system: Mercury, Venus, Earth, Mars, Jupiter,
Saturn, Uranus, Neptune and Pluto

The planets that make up our solar system are all very different. Some are near
to the sun, and experience very hot temperatures. Others are very far away, and

are much colder. Whilst Earth is just the right distance away to allow life to
flourish - not too hot, and not too cold!
The size of the planets also varies, from the tiny planet Pluto, to the gas giant
Jupiter - however all the planets have one thing in common - they all orbit the sun
(go around it) due to the sun’s gravity
Some planets, like Earth, have moons, which orbit the planet
It is the sun’s gravity (its pull force) which keeps all the planets orbiting around it
The force of gravity gets smaller as you get further away, meaning the closest
planets to the sun experience a strong force of gravity, whilst those further away
experience less
This means that it takes longer for the outer planets to orbit the sun - what else
do you think differs as you get further from the sun?

Moons are heavenly bodies which orbit other planets - gravity of the Earth keeps
our moon in orbit
Earth has one moon, but some planets have many of them
Earth’s moon has no atmosphere, so we could not live on it - in fact Earth’s Moon
is pretty boring - just a big lump of rock with lots of impact craters!
We only see the Moon because it reflects sunlight and it takes the moon 28 days
to orbit the Earth

As the Moon orbits the Earth we see different amounts of it - the different phases
of the Moon.
We can only see the part of the Moon which reflects sunlight, and this depends
on where the Moon is during its orbit around the Earth

Years and seasons
Years
A planet's year is the time it takes to make one complete orbit around the Sun.
The Earth goes once round the Sun in one Earth year. That's 365 Earth days.
We've seen already that different planets take different lengths of time to orbit the
Sun. That means their years are different lengths. Mercury has a year of just 88
Earth days, and Neptune has a year of 164 Earth years.
Seasons

The Earth's axis is the imaginary line through the centre of the Earth between the
South and North poles. This axis is tilted slightly compared to the way the Earth
orbits the Sun.

We get different seasons (winter, spring, summer and autumn) because the
Earth is tilted. This is how it works:

 When the northern hemisphere is tilted towards the Sun it is summer in
the UK.

 When the northern hemisphere is tilted away from the Sun it is winter in
the UK.

When it is summer in the northern hemisphere, it is winter in the southern
hemisphere.

Because of the tilt of the Earth's axis the Sun moves higher in the sky in summer,
when we tilt towards it, than in winter.

West East

Life & Deep Space
There are more than a billion galaxies in the universe - each galaxy has millions
of stars, of which the vast majority have planets orbiting them
So chances are somewhere in the universe there will be a planet similar to Earth,
able to support life (i.e. not too big; not too close / far from star)
Stars form from clouds of dust, which spiral together due to gravitational
attraction. The gravity compresses the matter so much that intense heat
develops, causing a nuclear fusion reaction
Stars emit light and radiation (unlike planets) due to this nuclear reaction - they
are the sources of light!
But remember - the sun is a star too! It just looks different to all the other twinkles
in the sky, because it is so much closer to us than any other star!

The stars seem to move across the sky because the Earth is rotating. Just like
we see the sun rise and set, the stars seem to move across the sky as the Earth
spins.
Constellations are groups of stars which may resemble something. We make up
constellations, so it makes it easier for us to spot individual stars
It helps as it breaks the night sky up into manageable bits, so you may be able to
identify a group of stars very quickly and easily, e.g. The Big Dipper

Particles Key Notes

Particles & Particle Arrangement
All materials are made up of particles. The particle theory says that all things
are made of tiny pieces, called particles. Solids, liquids and gasses all have
different arrangements of these particles, giving them their special properties.
Solids, liquids and gases are the three states of matter

Solids: -
 The particles are very close together
 The particles are arranged in a regular pattern
 The particles cannot move from place to place, but the particles can
vibrate in a fixed position
 Solids are held together by strong forces called bonds
 Solids have a fixed shape, e.g. wood, plastic, steel, ice (solid water)

Solids have a fixed shape because the particles cannot move from place to place

Solids cannot be compressed because the particles are very close together, and
have no space to move into

Liquids: -
 The particles are close together
 The particles are arranged in a random way
 The particles can move around each other - the bonds in a liquid are
strong enough to keep the particles together, but weak enough to let them
move around
 Liquids flow, and can change shape, e.g. water, lemonade, mercury, (all
liquids at room temp.)

Liquids can change shape because the particles can move around each other

Liquids cannot be compressed because the particles are close together, and
have no space to move into

Gases: -
 The particles are far apart
 The particles are arranged in a random way
 The particles can move quickly, in all directions - there are no bonds
between the particles in a gas
 Gases flow, and completely fill their container, e.g. air, helium, chlorine
(gas at room temp.)

Gases can move quickly in all directions, filling their container

Gases can be compressed because the particles are far apart, and have space
to move into

Heat

Melting (solid  liquid) such as ice to water. When a substance melts, the fixed
particles become able to move around each other.

Evaporating (liquid  gas) such as water to water vapour. When a substance
evaporates, some particles gain enough energy to move fast enough to escape
the force of attraction from the other particles and escape.

Condensing (gas  liquid) such as water vapour to water. When a substance
condenses, the high energy particles loose energy, and the force of attraction
from the other particles becomes sufficient to keep all the particles together
(although they can still flow other each other)

Freezing (liquid  solid) such as water to ice. When a substance freezes the
particles go from being able to move around each other, to being fixed in place

Boiling is very similar to evaporating (liquid  gas). When you evaporate a liquid,
some of the particles get enough energy to escape the force of attraction from
the other particles in the liquid.

Boiling is the same as this, but if you heat the liquid even more it will boil - this is
where virtually all the particles have enough energy to overcome the forces of
attraction and escape.

Expansion: -
 Substances expand (get bigger) when they are heated up. The particles
stay the same (the number of particles + their size is the same). But they
take up more room!
 Solids - particles vibrate more and take up more room
 Liquids - move around each other more quickly and take up more room
 Gases - move more quickly in all directions, and take up more room

Contraction: -
 Substances contract (get smaller) when they are cooled down
 When we cool objects, the number of particles and their size remains the
same; they just take up less room!

Diffusion

Diffusion is the net movement of particles from an area of high concentration, to
an area of low concentration

When a smelly gas such as a deodorant is let loose in a room, its particles mix
with the particles of air. The particles of smelly gas are free to move quickly in all
directions. Eventually they spread through the whole room - this is called
diffusion.

You don’t need to wave your arms around to mix the smelly particles - it mixes on
its own. Diffusion in gases is very quick, because the particles in a gas move
quickly, so they can get from one side of the class to the other quickly.

Diffusion is the mixing of particles, which occurs in gases and liquids but not
solids

Diffusion can occur in gases and in liquids, because their particles are able to
move

Diffusion is slower in liquids than in gases because the particles move more
slowly

But diffusion cannot occur in solids - this is because the particles are fixed in
place - they are not able to move (they can only vibrate), so do not mix

Before diffusion After diffusion

Adding heat to the gas or liquid causes diffusion to happen quicker. This is
because the particles have even more energy, and move around much quicker
(mixing quicker)

Gas Pressure

Gas pressure causes a balloon / tyre to keep its shape

The pressure is caused by the trapped gas particles colliding into the sides of the
container they are in

The more particles there are in there, the greater the pressure becomes (until
you try to put too many particles in, when often the balloon pops)!

If a gas is heated up, its particles move around more quickly. They will hit the
sides of the balloon harder, and more often. This will then increase the pressure
(and the balloon expands)

Heat it up too much, and you’ll create too much pressure inside, causing the
container to explode.

The opposite happens when you cool it - the particles move slower, crash into
the sides with less force, and less often, decreasing the pressure (so the balloon
shrinks)

Solute, Solvent & Solution Key Terms

 Solution - the mixture formed when a substance dissolves in it
 Solute - the substance that dissolves
 Solvent - the liquid in the solution
 Dissolve - mixing of a substance in a liquid
 Soluble - a substance which can dissolve (mix in a liquid)
 Insoluble - a substance which cannot dissolve (mix in a liquid)
 Saturated – the point at which no more solute can dissolve in the solvent
 Solubility – the amount of solute which can dissolve in our solvent

A solution is always transparent - even it has a colour. If our liquid remains
cloudy, then the solute has not completely dissolved. If a substance will not
dissolve (insoluble) then it will settle and be obvious.

When something dissolves its particles spread throughout the solvent, forming a
solution

The particles diffused quicker when they were heated - more heat gives them
more energy, so the move (and mix) quicker

The solubility of most substances increases as the temperature does

This means most substances become more soluble in hot water, rather than cold
water, meaning it becomes easier to wash our dishes!

Separating

Filtration can separate an insoluble solid from a liquid (remember insoluble
means it does not dissolve).

Evaporation can separate a soluble solid from a liquid (a soluble substance
dissolves in water to form a solution).

Evaporation helps us separate because some water particles are given enough
energy to escape the attraction of the other particles. If we heat the water for a
long enough, eventually all our particles are given enough energy to escape, just
leaving salt

Salt cannot be separated using filtration, because the particles are too well mixed
- this means that they would pass straight through the filter paper.

Distillation can separate a liquid from a solution (water from salty water).
Distillation works by evaporating the liquid from the solution. It is then cooled and
condensed into a separate container. The salt does not evaporate, so we have
successfully separated the two

It is really important you know the boiling temperature of the liquid you want

The liquid will only be removed once it reaches this boiling point (at which point it
can be condensed and collected)

This means different substances can be separated, based on their boiling
temperature - this is the science behind distillation

Chromatography is a way to separate dissolved substances, which have different
colours, such as ink and plant dyes

It works because some substances dissolve in the liquid better than the others.
The better a substance dissolves, the higher up the filter paper it travels

 The start line is drawn in pencil so more colour spots are not added!
 The molecules moved upwards
 The ink is drawn well above the solvent level to stop it dissolving in the

solvent

Earth Science Key Notes

Properties of rocks
A rock is made of grains that fit together. Each grain in the rock is made from a
mineral, which is a chemical compound
The grains in a rock can be different colours, shapes and sizes – this is what
gives them different textures
In some rocks the grains fit together and there are no gaps. Their grains are
interlocking and these rocks are sometimes called crystals

In other rocks the grains are rounded, and do not fit together (there are lots of
gaps). Their grains are non-interlocking

Rocks with rounded grains are more likely to absorb water than rocks with
interlocking grains because the water can get into the gaps between the grains.
Rocks that absorb water are called porous
Rocks with rounded grains are usually softer and more crumbly than rocks with
interlocking grains
Sedimentary, igneous and metamorphic rocks
Sedimentary rocks often have layers showing deposition of sediment through
different time periods

Sedimentary rocks consist of lots of small grains – these grains are often weakly
held together, so the rocks are soft and crumbly (as well as often being porous)
Sedimentary rocks has the oldest layers at the bottom and the youngest layers at
the top
Sedimentary rocks may contain fossils of animals and plants trapped in the
sediments as the rock was formed – fossils are only found in sedimentary rocks

 Rocks are deposited at the bottom of a lake / sea (after being transported
from rivers)

 The deposited rocks build up in layers, called sediments (this is
sedimentation)

 The weight of the sediments on top squashes the sediments at the bottom
(compaction)

 The water is squeezed out from between the pieces of rock and crystals of
different salts form – the crystals form a sort of glue that sticks or cements
the pieces of rock together (cementation) which may take millions of years
Sedimentation  Compaction  Cementation

As soon as plants and animals die they begin to rot away – however, sometimes
the dead plants and animals can be turned into fossils (rock copies of the original
plant or animal)
Fossils forms when dead plants or animals become covered in a layer of
sediment, which initially protects them…

 An organism dies, and settles on the sea floor

 Gradually it is covered with sediment, which protects it, and over time the
layers build up

 As the layers build up the pressure increases, causing sedimentary rock to
form

 The dead organism undergoes a series of chemical changes resulting in
rock-like minerals taking the place of the original chemicals

 Over millions of years the original organism is replaced with minerals, and
a rock-like copy of the organism is left

The earliest fossils are found in the deepest parts of the rock (over time more
and more sediment is laid down, meaning organisms which dies the longest time
ago are found in the deepest parts)

Igneous rocks are formed within the Earth (where temp. is hot enough to melt
rock)
Molten (liquid) rock forms when rocks melt, called magma. When the magma
cools and solidifies igneous rocks are formed

Igneous rocks contain interlocking crystals, which are held together very
strongly and make the rock hard

The crystals in igneous rocks have a disorderly arrangement
Igneous rocks never contain fossils (as the rock has been melted, destroying the
fossils)
When magma cools above the surface, extrusive igneous rocks are formed
When magma cools below the surface, intrusive igneous rocks are formed
If the rock cools slowly there is time for lots of particles to move and stick
together (bond) = large crystals
If the rock cools quickly only a few particles can move and stick (bond) together =
small particles

Metamorphic rocks are formed from existing sedimentary rocks that are changed
because of heat or pressure
Earth movements may cause rocks to be deeply buried or squeezed - these
rocks are heated and put under great pressure but they do not melt (if they melt
they become igneous rocks)
The minerals they contain are changed chemically, forming metamorphic rocks

The Rock Cycle
The Earth's rocks do not stay the same forever
They are continually changing due to processes such as weathering Earth
movements - the rocks are gradually recycled over millions of years – this is the
rock cycle

Rock weathering & how water shapes the land
Rocks are different shapes and sizes because they are changed by the
conditions in their environment
Rocks gradually wear away – this is known as weathering
There are three types of weathering: -

1. Physical weathering
2. Chemical weathering
3. Biological weathering
Physical weathering is caused by changes such as changes in temperature,
freezing and thawing, and the effects of wind, rain and waves…

Temperature - when a rock gets hot it expands a little, and when a rock gets cold
it contracts a little. If a rock is heated and cooled many times, cracks form and
pieces of rock fall away (this type of physical weathering happens a lot in
deserts, because it is very hot during the day but very cold at night)
Freezing and thawing – water expands when it freezes

 If water gets into a crack in a rock and then freezes, it expands and
pushes the crack further apart

 When the ice melts later, water can get further into the crack
 When the rock freezes again, it expands and makes the crack even bigger

- this process of freezing and thawing can continue until the crack
becomes so big that a piece of rock falls off
Wind, rain and waves – the wind can blow tiny grains of sand against a rock
wearing the rock away and weathering it
Chemical weathering is caused because rainwater is naturally slightly acidic
because carbon dioxide from the air dissolves in it

Minerals in rocks may react with the rainwater, causing the rock to be weathered
– this is chemical weathering

Some types of rock are easily weathered by chemicals, such as limestone and
chalk whilst some types of rock are not easily weathered by chemicals, such as
granite and gabbro

The burning of fossil fuels produces oxides of sulphur and nitrogen, causing rain
to become more acidic (acid rain)
This type of acid rain reacts more quickly with rock minerals, weathering them
more rapidly

Biological weathering is where animals and plants wear away rocks. Burrowing
animals such as rabbits can burrow into a crack in a rock, making it bigger and
splitting the rock
Plant roots can grow in cracks – as they grow bigger, the roots push open the
cracks and make them wider and deeper, eventually causing pieces of rock to fall
away
People can cause biological weathering by walking. Over time, paths in the
countryside become damaged due to the boots wearing them away
Weathering is the wearing away of rocks – this can be via a physical, chemical,
or biological process
Erosion is the movement of the broken pieces away from the site of weathering

Rivers and streams can move pieces of rock – this is transportation
Fast flowing rivers can transport large rocks, but slow moving rivers can only
transport tiny pieces of rock
As the pieces of rock are carried along by the water, they bash against each
other and the river bed, gradually wearing away become smaller and more
rounded

Finally the transported rocks are deposited when the river does not have enough
energy to carry them
Very large rocks need a huge amount of energy to carry them – as the river
slows energy is lost causing the large rocks to be deposited first
Acid rain
Normal rainwater has a pH of around 5.6 – this means it is naturally slightly
acidic. This natural acidity is due to CO2, which dissolves in rainwater, forming
carbonic acid
Acid rain has a higher than normal acid level (a low pH). Acid rain may contain
weak solutions of carbonic, sulphuric, and nitric acids
Where it falls over a prolonged period it can cause damage to the environment…

These chemicals can occur naturally, for example sulphur is released at active
volcanic sites
However, the vast majority of these chemicals are pollutants, produced from cars
and power stations
When these dissolve in rainwater they produce strong acids (sulphuric acid and
nitric acid) forming acid rain

Acid rain can be devastating: -
 Trees lose some of the protection in their leaves, leaving them more at
risk from frost and diseases
 Tree roots may also become stunted, so they can't take up as many
nutrients
 Soils lose some of their nutrients
 Increasing acid levels may cause problems for aquatic animals and plants
(e.g. fish may have trouble breathing)
 Acid rain may dissolve the stonework and mortar of buildings causing
structural problems

Acid rain pollution may also cause acid rain many miles away from the source

Sulphur dioxide is formed when coal, containing sulphur, is burned in power
stations – this can be removed within the power station before being released
into the atmosphere
Nitrogen oxides are formed when petrol burns in vehicle engines – this can be
converted into harmless gases using a catalytic converter

Acid rain can dissolve rocks, which release carbon dioxide (a greenhouse gas)
Acid rain also increase soli acidity, inhibiting plant growth (which usually absorb
CO2)
Ozone

The Earth is surrounded by a deep layer of gas called the atmosphere (a mixture
of gases, including nitrogen, oxygen, argon and carbon dioxide)

Oxygen in the atmosphere can change its physical state from O2 to O3 which is
know as ozone

There is very little ozone at ground level but much more at very high altitudes (in
the stratosphere)
The ozone layer protects us from harmful rays emitted by the sun
Ultra-violet light (UV) can cause both skin cancer and damage to the eyes, such
as cataracts (this is where the lens does not allow light to pass through easily,
blurring vision)
In the past century we have been rather good at damaging the ozone layer…
This has been via the use of chlorofluorocarbons (CFCs), e.g. fly spray;
refrigerator coolants; aerosol sprays – the chlorine reacts with O3 and breaks it
down. Highflying jet aircraft exhaust gases also react with the ozone: Concorde
was especially bad for this

If the ozone continues to be destroyed as it is then we will experience a much
higher concentration of the UV radiation emitted by the sun, which can cause
skin cancer