Major topics Low stake topics TJNOTES
GCSE Chemistry Notes
PAPER I
Atoms, Elements and Cmpounds
• An element is a substance that only contains one type of atom (each atom has the
same number of protons)
• Compounds = contain two or more different elements chemically combined in a
fixed proportion – for example, magnesium sulfide
• Compounds will often have completely different properties to the elements from
which they were produced – if we want to separate a compound back into its
elements, we need to use a chemical reaction
• Mixtures = contain different elements or compounds not chemically bonded
together – to separate mixtures, we use physical separation techniques rather
than chemical reactions
• Chemical reactions involve the formation of new products and substances, and
also tend to have a detectable energy change
• Just remember compounds ≠ molecules – compounds must be two or more
different elements joined together, molecules are just two or more of any
elements joined together, they could be the same element
Mixtures and Separation
• Physical separation techniques are used to separate mixtures only NOT
compounds
There are 4 physical separation techniques:
(1) Filtration – used to separate an insoluble solid from a liquid it is suspended
(not dissolved) in
• To do this, we use a filter funnel and filter paper folded in the shape of a cone
• Pour the mixture into the filter paper and funnel, the solid is too large to fit
through the pores of the filter paper so only the water passes through and solid
remains on the filter paper – so they are separated
• (2) Crystallisation – used to obtain and separate a soluble solid from a liquid
that it is dissolved in
• We can either leave the solution to evaporate slowly at room temperature or we
can heat it using a Bunsen burner, tripod and gauze
• This causes the water to evaporate, leaving crystals of the solid behind, this
works because water will have a lower boiling point than the solid dissolved in it
,Major topics Low stake topics TJNOTES
(3) Simple distillation – this is used, like crystallisation, to separate a soluble
solid from a liquid. However, this is used when we actually want to keep the
liquid, and cannot simply evaporate it off
• First, we evaporate the liquid by heating it to a high enough temperature using a
Bunsen burner and then condensing the vapour by cooling it in another
container
(4) Fractional distillation – this is used to separate a mixture of 2 different
liquids. These liquids must have different boiling points for this physical
separation technique to work
• We connect a flask to a fractionating column full of glass beads and again to a
condenser and another beaker
• Heat the flask using a Bunsen burner until the temperature of the thermometer
at the top of the column reaches the boiling point of the first liquid
• At this point, both liquids will be evaporating but only the liquid with the higher
boiling point will condense and drop back down once it reaches the top of the
column. The lower boiling point liquid will not condense and will pass into the
condenser, cool and form a pure liquid. The remaining liquid will be the other
higher-boiling point liquid
• If the two liquids have similar boiling points, it is much harder to separate them
(5) Chromatography – used to separate substances in a solution based on their
different solubilities
• Again, here no chemical reactions take place, and no new substances are made
because it is a physical separation technique
• Draw a pencil line on the bottom of chromatography paper (pencil does not
dissolve in the solvent)
• Draw a dot of first colour on pencil line and dot of second colour on the pencil
line
• Place bottom of paper in solvent (a liquid that allows substances to dissolve into
it) like water and ethanol
• The solvent makes its way up the paper and the ink is dissolved into it
• Due to the different solubilities, the different substances in the mixture will
travel up the paper at different rates depending on its attraction to the stationary
or mobile - highly unlikely you’ll be asked on this on paper 1 bc it is low-stakes +
a small topic
,Major topics Low stake topics TJNOTES
Development of the model of the atom
The very early model of the atom was JJ Thomson’s plum pudding model:
• The plum pudding model described the atom as a ball of positive charge with
electrons embedded within it
• However, Rutherford conducted an alpha particle scattering experiment
whereby positively-charged alpha particles were fired at an extremely thin sheet
of gold foil
• If the plum pudding model was true, the particles should have passed straight
through or only be slightly deflected at most because the positive charge was
thought to be very spread out throughout the atom
• But, whilst most particles did go straight through, a small number of particles
were deflected more than expected and a small number were even deflected
backwards, so plum pudding could not be right
• Rutherford came up with the idea of the nuclear model of the atom where there
is a small, positively charged nucleus at the centre where most of the mass and
positive charge is concentrated with a cloud of electrons surrounding the
nucleus and the atom being mainly empty space
• The fact that a small number of positive alpha particles were deflected meant
that the mass wasn’t evenly spread out and that positive charge must be
concentrated in the centre
• Later on, Bohr realised that the cloud of electrons wouldn’t work as the electrons
would be attracted to the nucleus, causing atom to collapse
• Bohr’s model suggested that all electrons orbited the nucleus in shells and aren’t
anywhere in between – his theory of atomic structure was then supported by
many experiments and helped to explain other observations of the time
,Major topics Low stake topics TJNOTES
• Years later, Rutherford and others gave the conclusion that the nucleus could be
divided into smaller particles with the same charge as hydrogen nuclei (protons)
• Chadwick carried out experiments which provided the evidence for neutral
particles in the nucleus – these later became known as neutrons
, Major topics Low stake topics TJNOTES
Atoms
• Atoms are the tiny particles everything is made up of, with a radius of about
1x10-10 metres
• This shows the nuclear model of the atom (the widely accepted model)
• The nucleus is in the middle of the atom, it contains protons and neutrons
• Protons are positively charged and neutrons have no charge (neutral) so the
overall charge of the nucleus is positive due to the protons
• The nucleus is tiny compared to the rest of the atom – the radius is 1x10-4 which
is 1/10000 the size of the atom
• Electrons orbit the nucleus in distinct shells/energy levels
• Electrons are negatively charged
• They are tiny but cover a lot of space
• They have virtually no mass in comparison to protons and neutrons but its
relative charge is the same value as the proton except negative
• An atom always has a neutral overall charge (the only time when an atom is not
neutral is when it gains or loses an electron and becomes an ion not an atom)
• Therefore, it makes sense that the number of protons = the number of electrons
in the atom
• We can use the idea that no. of protons=no. of electrons to calculate the numbers
of protons, electrons and neutrons in the atom using its periodic table symbol:
GCSE Chemistry Notes
PAPER I
Atoms, Elements and Cmpounds
• An element is a substance that only contains one type of atom (each atom has the
same number of protons)
• Compounds = contain two or more different elements chemically combined in a
fixed proportion – for example, magnesium sulfide
• Compounds will often have completely different properties to the elements from
which they were produced – if we want to separate a compound back into its
elements, we need to use a chemical reaction
• Mixtures = contain different elements or compounds not chemically bonded
together – to separate mixtures, we use physical separation techniques rather
than chemical reactions
• Chemical reactions involve the formation of new products and substances, and
also tend to have a detectable energy change
• Just remember compounds ≠ molecules – compounds must be two or more
different elements joined together, molecules are just two or more of any
elements joined together, they could be the same element
Mixtures and Separation
• Physical separation techniques are used to separate mixtures only NOT
compounds
There are 4 physical separation techniques:
(1) Filtration – used to separate an insoluble solid from a liquid it is suspended
(not dissolved) in
• To do this, we use a filter funnel and filter paper folded in the shape of a cone
• Pour the mixture into the filter paper and funnel, the solid is too large to fit
through the pores of the filter paper so only the water passes through and solid
remains on the filter paper – so they are separated
• (2) Crystallisation – used to obtain and separate a soluble solid from a liquid
that it is dissolved in
• We can either leave the solution to evaporate slowly at room temperature or we
can heat it using a Bunsen burner, tripod and gauze
• This causes the water to evaporate, leaving crystals of the solid behind, this
works because water will have a lower boiling point than the solid dissolved in it
,Major topics Low stake topics TJNOTES
(3) Simple distillation – this is used, like crystallisation, to separate a soluble
solid from a liquid. However, this is used when we actually want to keep the
liquid, and cannot simply evaporate it off
• First, we evaporate the liquid by heating it to a high enough temperature using a
Bunsen burner and then condensing the vapour by cooling it in another
container
(4) Fractional distillation – this is used to separate a mixture of 2 different
liquids. These liquids must have different boiling points for this physical
separation technique to work
• We connect a flask to a fractionating column full of glass beads and again to a
condenser and another beaker
• Heat the flask using a Bunsen burner until the temperature of the thermometer
at the top of the column reaches the boiling point of the first liquid
• At this point, both liquids will be evaporating but only the liquid with the higher
boiling point will condense and drop back down once it reaches the top of the
column. The lower boiling point liquid will not condense and will pass into the
condenser, cool and form a pure liquid. The remaining liquid will be the other
higher-boiling point liquid
• If the two liquids have similar boiling points, it is much harder to separate them
(5) Chromatography – used to separate substances in a solution based on their
different solubilities
• Again, here no chemical reactions take place, and no new substances are made
because it is a physical separation technique
• Draw a pencil line on the bottom of chromatography paper (pencil does not
dissolve in the solvent)
• Draw a dot of first colour on pencil line and dot of second colour on the pencil
line
• Place bottom of paper in solvent (a liquid that allows substances to dissolve into
it) like water and ethanol
• The solvent makes its way up the paper and the ink is dissolved into it
• Due to the different solubilities, the different substances in the mixture will
travel up the paper at different rates depending on its attraction to the stationary
or mobile - highly unlikely you’ll be asked on this on paper 1 bc it is low-stakes +
a small topic
,Major topics Low stake topics TJNOTES
Development of the model of the atom
The very early model of the atom was JJ Thomson’s plum pudding model:
• The plum pudding model described the atom as a ball of positive charge with
electrons embedded within it
• However, Rutherford conducted an alpha particle scattering experiment
whereby positively-charged alpha particles were fired at an extremely thin sheet
of gold foil
• If the plum pudding model was true, the particles should have passed straight
through or only be slightly deflected at most because the positive charge was
thought to be very spread out throughout the atom
• But, whilst most particles did go straight through, a small number of particles
were deflected more than expected and a small number were even deflected
backwards, so plum pudding could not be right
• Rutherford came up with the idea of the nuclear model of the atom where there
is a small, positively charged nucleus at the centre where most of the mass and
positive charge is concentrated with a cloud of electrons surrounding the
nucleus and the atom being mainly empty space
• The fact that a small number of positive alpha particles were deflected meant
that the mass wasn’t evenly spread out and that positive charge must be
concentrated in the centre
• Later on, Bohr realised that the cloud of electrons wouldn’t work as the electrons
would be attracted to the nucleus, causing atom to collapse
• Bohr’s model suggested that all electrons orbited the nucleus in shells and aren’t
anywhere in between – his theory of atomic structure was then supported by
many experiments and helped to explain other observations of the time
,Major topics Low stake topics TJNOTES
• Years later, Rutherford and others gave the conclusion that the nucleus could be
divided into smaller particles with the same charge as hydrogen nuclei (protons)
• Chadwick carried out experiments which provided the evidence for neutral
particles in the nucleus – these later became known as neutrons
, Major topics Low stake topics TJNOTES
Atoms
• Atoms are the tiny particles everything is made up of, with a radius of about
1x10-10 metres
• This shows the nuclear model of the atom (the widely accepted model)
• The nucleus is in the middle of the atom, it contains protons and neutrons
• Protons are positively charged and neutrons have no charge (neutral) so the
overall charge of the nucleus is positive due to the protons
• The nucleus is tiny compared to the rest of the atom – the radius is 1x10-4 which
is 1/10000 the size of the atom
• Electrons orbit the nucleus in distinct shells/energy levels
• Electrons are negatively charged
• They are tiny but cover a lot of space
• They have virtually no mass in comparison to protons and neutrons but its
relative charge is the same value as the proton except negative
• An atom always has a neutral overall charge (the only time when an atom is not
neutral is when it gains or loses an electron and becomes an ion not an atom)
• Therefore, it makes sense that the number of protons = the number of electrons
in the atom
• We can use the idea that no. of protons=no. of electrons to calculate the numbers
of protons, electrons and neutrons in the atom using its periodic table symbol:
