Atoms and Molecules

• Everything is made up of tiny particles called atoms
• Atoms are too small to be seen except with the world’s most powerful microscopes
• There are over 100 different types of atom
• Atoms can join together with links called chemical bonds

Atoms are made up of protons, neutrons and electrons The protons and neutrons are gathered together in the nucleus Protons carry a single positive electrical charge Neutrons have no electrical charge Around the nucleus are the electrons Each electron carries a single negative electrical charge Normally the number of protons and electrons are the same and so electrical charges cancel out: An atom has no overall electrical charge

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Atoms are identified by their atomic number and mass number

• The atomic number of an atom is the number of protons in its nucleus
  • The illustrated atom has atomic number 2
  • The atomic number decides what kind of atom it is
• The mass number is the total number of protons and neutrons
  • Protons and neutrons have a mass of 1 AMU (atomic mass units)
  • Electrons have such a tiny mass that it is not important in labelling atoms

Each atom is described as follows

the illustrated atom is Helium – this would be written as;

The Periodic Table

The periodic table is divided into metals at the left and non-metals at the right

• Metals are shiny and conduct heat and electricity well.
• Non-metals are usually dull coloured and do not conduct electricity or heat well.

The periodic table is divided into 8 groups numbered 1-7 then 0:

• Chemicals in each group have similar properties.

The periodic table is divided up into rows called Periods

• The properties of chemicals change as you go along a period.

In between group 2 and 3 are the transition metals

Elements in the Periodic Table

• Group 1 of the periodic table contains the alkali metals: Group 2 contains the alkali earth metals.
  • In water these react to form an alkali.
  • In water they also give off hydrogen gas.
• Group 7 are called halogens:
  • They are non-metals.
  • They are poisonous.
  • They are coloured.
• Group 0 are the noble gases
  • They do not combine with other elements to form compounds

Solids Liquids and Gases

• Most elements in the periodic table are solid:
  • A solid has a fixed volume and a fixed shape.
• Mercury and Bromine are liquids:
  • Liquids have a fixed volume, but take the shape of their container.
• Some elements are gases:
  • A volume of a gas changes to fill the container and its shape changes to fit its container.
  • The noble gases on group 0 are all gases, so are Nitrogen, Oxygen, Fluorine, Chlorine and Hydrogen.
  • Hydrogen is a transparent, odourless gas which is lighter than air:
    • It burns with a pop.
    • It is used in weather balloons, to make margarine, and as an alternative fuel in cars.
  • Oxygen is a transparent, odourless gas:
    • It relights a glowing splint.
    • It is used in breathing equipment, cutting equipment (oxy-acetylene) and for breathing.
  • Nitrogen is a transparent, odourless gas:
    • Nitrogen will not support burning
    • It is found in fertilisers
    • The air is mostly nitrogen and oxygen but there are some other gases in the air, these make up the remaining 1%
      • Nitrogen – 78%
      • Oxygen – 21%
      • Other gases – 1%

Chemical Reactions

Atoms can join together chemically to make different substances:

• A molecule is a group of atoms held together chemically.
• An element is a substance that is made up of one type of atom.

• A compound is a substance in which two or more elements are joined together chemically.

• When a compound is made, by combining elements – heat energy is given out.
  

• To split a compound into its elements; energy must be put in:
• Some compounds can be split into elements by using electrical energy.
  • This is called electrolysis

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• The word equation for this reaction is
  • Nickel chloride ® nickel + chlorine

• Oxygen and iron (or steel) combine to form the compound iron oxide
  • Iron oxide is commonly called rust;:
  • Water must be present for rusting to occur.
  • The word equation for this is:
    • Iron + oxygen ® iron oxide.
    • We say this as “iron reacts with oxygen to give iron oxide”.
  • We call iron and oxygen the reactants.
  • We call iron oxide the product.

• Iron and steel can be protected from rust by:
  • Oil and grease
  • Painting
  • Covering with plastic
  • Coating with zinc (galvanising)
    

• When sodium reacts with chlorine the word equation is:
  • Sodium + chlorine ® sodium chloride.
  • The chemical equation is: Na + Cl ® NaCl.

• Two elements join together chemically to form a compound.
  • The ending –ide on the word chloride tells us there is no oxygen in the compound.
  • There are only sodium atoms and chlorine atoms in sodium chloride.

• Some chemicals such as copper sulphate have an –ate ending:
  • The chemical equation is
  • 2Cu + S + 40 ® Cu₂SO₄
  • This means that there is oxygen in the compound.
  • The compound contains copper, sulphur and oxygen.

Vocabulary

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