Complete Chemistry Revision Notes - AQA GCSE chemistry
1. Atomic structure and the periodic table
Atoms, elements and compounds
All substances are made of atoms and it is the simplest unit of matter. There are about
100 different types of atom found naturally on Earth.
Some substances are made up of only one type of atom. These substances are called
elements.
Elements differ from each other by their properties. Elements such as copper, silver and
gold are shiny, solid metals. Some elements such as oxygen, nitrogen, and chlorine are
non-metals, and they remain as gases at room temperature.
Element such as mercury and bromine are liquids. Each atom has its own symbol .
• Elements are listed in the periodic table. There are about 100 different elements.
• Elements can be classified as metal or non-metal depending on their properties.
• The columns in the periodic table are called groups and contain similar elements.
• The rows in the periodic table are called periods. Elements show a gradual change
in properties across a period
These different atoms combine in different ways and in different ratios to give
compounds.
Element: Elements contain only one type of atom
Compound: Compounds contain more than one type of atom.
• Compounds are formed from elements by chemical reactions. Chemical
reactions always involve the formation of one or more new substances, and often
involve a detectable energy change.
• Compounds contain two or more elements chemically combined in fixed
proportions and can be represented by formulae using the symbols of the atoms
from which they were formed.
• Compounds can only be separated into elements by chemical reactions.
Chemical reactions can be represented by word equations or equations using
symbols and formulae.
,Complete Chemistry Revision Notes - AQA GCSE chemistry
• Compounds are made up of different types of atom bonded together . Some
compounds are made from just two types of atom (e.g., water, made from atoms
of hydrogen and oxygen). However, most compounds consist of more than two
different types of atom.
Mixtures
A mixture consists of two or more elements or compounds not chemically combined
together. Mixtures can be separated by physical processes such as filtration,
crystallisation, simple distillation, fractional distillation and chromatography. These
physical processes do not involve chemical reactions and no new substances are made.
Separating Techniques- You will learn this section in detail in Chemical analysis.
Mixtures can be separated by physical processes such as filtration, crystallisation, simple
distillation, fractional distillation and chromatography. These physical processes do not
involve chemical reactions.
Simple distillation
Type of mixture separated: soluble solid dissolved in a liquid (usually water) e.g.
salty water
Two soluble liquids can be separated base on their boiling points. e.g. separation of
alcohol from water
liquid boils off and condenses in the condenser. The thermometer will read the boiling
point of the pure liquid.
, Complete Chemistry Revision Notes - AQA GCSE chemistry
Fractional distillation
Type of mixture separated:
Soluble liquids with different boiling points e.g. crude oil , mixture of alcohols
The fractionating column has a temperature gradient and is hotter at the bottom than at
the top.
When a mixture of soluble liquids is heated all liquids are evaporated. The liquid with
the lower boiling point, however, forms the greatest percentage of vapour.
As the vapour moves up the fractionating column it becomes more rich with the
component that has the lowest boiling point. This is due to the vapour mixture
condensing and evaporating as it moves up the column.
A thermometer measures the temperature of the fractions before they condense. The
liquid with the lowest boiling point will be the first 'fraction' to collect.
1. Atomic structure and the periodic table
Atoms, elements and compounds
All substances are made of atoms and it is the simplest unit of matter. There are about
100 different types of atom found naturally on Earth.
Some substances are made up of only one type of atom. These substances are called
elements.
Elements differ from each other by their properties. Elements such as copper, silver and
gold are shiny, solid metals. Some elements such as oxygen, nitrogen, and chlorine are
non-metals, and they remain as gases at room temperature.
Element such as mercury and bromine are liquids. Each atom has its own symbol .
• Elements are listed in the periodic table. There are about 100 different elements.
• Elements can be classified as metal or non-metal depending on their properties.
• The columns in the periodic table are called groups and contain similar elements.
• The rows in the periodic table are called periods. Elements show a gradual change
in properties across a period
These different atoms combine in different ways and in different ratios to give
compounds.
Element: Elements contain only one type of atom
Compound: Compounds contain more than one type of atom.
• Compounds are formed from elements by chemical reactions. Chemical
reactions always involve the formation of one or more new substances, and often
involve a detectable energy change.
• Compounds contain two or more elements chemically combined in fixed
proportions and can be represented by formulae using the symbols of the atoms
from which they were formed.
• Compounds can only be separated into elements by chemical reactions.
Chemical reactions can be represented by word equations or equations using
symbols and formulae.
,Complete Chemistry Revision Notes - AQA GCSE chemistry
• Compounds are made up of different types of atom bonded together . Some
compounds are made from just two types of atom (e.g., water, made from atoms
of hydrogen and oxygen). However, most compounds consist of more than two
different types of atom.
Mixtures
A mixture consists of two or more elements or compounds not chemically combined
together. Mixtures can be separated by physical processes such as filtration,
crystallisation, simple distillation, fractional distillation and chromatography. These
physical processes do not involve chemical reactions and no new substances are made.
Separating Techniques- You will learn this section in detail in Chemical analysis.
Mixtures can be separated by physical processes such as filtration, crystallisation, simple
distillation, fractional distillation and chromatography. These physical processes do not
involve chemical reactions.
Simple distillation
Type of mixture separated: soluble solid dissolved in a liquid (usually water) e.g.
salty water
Two soluble liquids can be separated base on their boiling points. e.g. separation of
alcohol from water
liquid boils off and condenses in the condenser. The thermometer will read the boiling
point of the pure liquid.
, Complete Chemistry Revision Notes - AQA GCSE chemistry
Fractional distillation
Type of mixture separated:
Soluble liquids with different boiling points e.g. crude oil , mixture of alcohols
The fractionating column has a temperature gradient and is hotter at the bottom than at
the top.
When a mixture of soluble liquids is heated all liquids are evaporated. The liquid with
the lower boiling point, however, forms the greatest percentage of vapour.
As the vapour moves up the fractionating column it becomes more rich with the
component that has the lowest boiling point. This is due to the vapour mixture
condensing and evaporating as it moves up the column.
A thermometer measures the temperature of the fractions before they condense. The
liquid with the lowest boiling point will be the first 'fraction' to collect.
