Elements and Reactivity Revision Notes
Elements
• There are just over 100 elements in the Periodic Table.
• Elements are made up of one type of atom.
• Every element has a name, atomic number and symbol.
Element Symbols
• Each element can be represented by a one or two letter symbol.
• The first letter is always a capital letter, if there is a second letter in
the symbol it is lower case.
• e.g. C is the symbol for carbon ; Cl is the symbol for chlorine
Arrangement of Elements in the Periodic Table
Elements can be sorted in different ways:
• metals and non-metals
• solids, liquids and gases
• naturally occurring and man-made
Metals and Non-Metals
Metals
Examples: Copper, Tin and Lithium
Most elements in the Periodic Table are
metals and they are found to the left-hand side.
Non-Metals
Examples: Nitrogen and Carbon
Poor conductors of heat and electricity
Low melting and boiling points
Solids, Liquids and Gases
Examples of solids: Magnesium, Carbon and Sulphur
Examples of Liquids: Mercury and Bromine
Examples of Gases: Oxygen, Nitrogen and Helium
Natural and Man-Made
Examples of Natural: Copper and Hydrogen
Examples of Man-made: Californium and Einsteinium
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Groups in the Periodic Table
Elements with similar properties are found in the same vertical column. This is
called a group.
Group 1- The Alkali Metals
• These elements are very reactive and so are stored under oil.
• They all react quickly with water releasing hydrogen gas and forming an
alkaline solution.
• As you go down Group 1 the metals become more reactive.
Group 7- The Halogens
• These elements have coloured vapours and are very reactive.
• As you go down the group the elements become less reactive and the
melting and boiling points get higher.
Group 8/0- The Noble Gases
• These elements are very unreactive (inert).
• Argon is used in filament lamps
• Helium is lighter than air and used in balloons
Structure of the Atom
• All atoms have a small central nucleus containing
protons and neutrons
• Particles called electrons orbit the nucleus
• Protons, neutrons and electrons have different
masses and charges
Particle
Proton
Electron
Neutron
Charge
+1
-1
0
Location
Found inside the nucleus
Found in energy levels around the nucleus
Found inside the nucleus
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Mass
1
~0
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Atomic Number
• All elements in the Periodic Table are listed in order of increasing atomic
number.
• The atomic number is the number of protons there are in the nucleus of
an atom.
• In an atom, the number of negative electrons always equals the number
of positive protons.
• Atoms therefore do not have an overall electrical charge- they are
neutral.
Molecules, Mixtures and Compounds
Molecules
• Molecules are small groups of atoms are joined
together.
• Molecules of an element contain only one type of atom
e.g. an oxygen molecule contains only oxygen atoms.
Compounds
• Compounds are new substances formed when atoms of
two or more elements chemically join together.
• Molecules of a compound contain two or more types of
atom e.g. H2O is a molecule of water.
Mixtures
• A mixture is a collection of two or more substances,
elements or compounds, which are not chemically joined.
• Air is an example of a mixture of gases:
– 79% Nitrogen
– 20% Oxygen
– 1% Other Gases.
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Chemical Formulae
• The chemical formula of a substance tells us the elements that present
and how many atoms of each element there are in a molecule of the
substance.
e.g. the formula for carbon dioxide is CO2. It
contains one carbon atom and two oxygen atoms.
Substance
Formul
a
Name and type of
atoms in molecule
Element or
Compound
Water
HO
2 Hydrogen atoms
1 Oxygen atom
Compound
Hydrogen
H
2 Hydrogen atoms
Element
Methane
CH
1 Carbon atom
4 Hydrogen atoms
Compound
2
2
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Naming compounds
Compounds with a name ending in -ide contain the two elements indicated in
the name.
A compound ending –ite or –ate means that the compound contains three
elements, one of which is oxygen.
Examples
Sodium Sulphate contains the elements Sodium, Sulphur and Oxygen.
Lead nitrite contains the elements Lead, Nitrogen and Oxygen.
Copper chloride contains the elements Carbon and Chlorine.
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Breaking up Compounds
• Breaking up compounds into their elements is usually much more difficult
than making compounds.
• Some compounds can be broken up using Electrolysis
• Electrolysis uses electricity to breakdown a compound into its elements.
Electrolysis of Copper Chloride
• Copper chloride is a compound that can be broken up into its elements,
copper and chlorine, by passing an electric current through a solution of
it.
• This is called electrolysis.
• Brown copper metal forms at the negative electrode and bubbles of
chlorine gas form at the positive electrode.
Chemical Reactions
• When a chemical reaction occurs a new substance is always formed.
Signs of a Chemical Reaction
When a chemical reaction occurs a new substance is always formed.
Some signs that show that a chemical reaction has occurred include:
• a gas being given off
• a solid forming
• a colour change
• a temperature change in the reaction mixture
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Metal Ores
• Most metals have to be extracted from naturally occurring compounds in
the earth’s crust called metal ores.
• The more reactive a metal is the more difficult it is to extract from its
compounds.
Breaking up Copper oxide and Silver oxide
• Copper metal can be extracted from the compound copper oxide by
heating it with carbon powder.
copper oxide + carbon  copper + carbon dioxide
• Silver is a very unreactive metal. Silver can be obtained from silver oxide
by heating alone.
silver oxide  silver + oxygen
Rates of Reaction
• Three factors which can affect the speed of a chemical reaction are:
– particle size of reactants
– temperature
– concentration of reactants
When two reactions are compared only one variable should be changed to
make the comparison fair.
Particle Size of Reactants
As the particles size of the
reactants decreases, the speed of
the reaction increases.
This is because when smaller
particles are used, there is a larger
surface area.
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Concentration of Reactants
As the concentration of
reactants increases, the
speed of the reaction also
increases.
Temperature of Reactants
As the temperature of the
reactants increases, the
speed of the reaction also
increases.
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