The periodic table

All the different elements are arranged in a chart called the periodic table. A Russian scientist called Dmitri Mendeleev produced one of the first practical periodic tables in the 19th century. The modern periodic table is based closely on the ideas he used:

  • the elements are arranged in order of increasing atomic number
  • the horizontal rows are called periods
  • the vertical columns are called groups
  • elements in the same group are similar to each other
A section of the periodic table showing metals and non-metalsA section of the periodic table showing metals and non-metals

The main groups are numbered from 1 to 7 going from left to right, and the last group on the right is group 0. The section in the middle of the table is called the Transition Metals. You may also see all the groups numbered (including the transition metals), this time from 1 to 18. If you know what one of the elements in a group is like, you can make predictions about the other elements in a group. For example, all the elements in group 1 are reactive metals, and all the elements in group 0 are unreactive non-metals.

The zig-zag line in this diagram separates the metals, on the left, from non-metals, on the right. Hydrogen is a non-metal but it is often put in the middle.

Notice that most elements are metals, rather than non-metals.

Each element has its own chemical symbol, made from letters. Remember that you will only find elements in the periodic table and never compounds. So you won’t find substances like water or copper sulfate in the periodic table.

Making predictions using the periodic table

Groups in the periodic table contain elements with similar chemical properties. But there are usually trends in properties that allow us to make predictions. For example, in group 1:

Melting pointDensityReactivity
LithiumDecreases down the groupIncreases down the groupIncreases down the group
SodiumDecreases down the groupIncreases down the groupIncreases down the group
PotassiumDecreases down the groupIncreases down the groupIncreases down the group
RubidiumDecreases down the groupIncreases down the groupIncreases down the group

Caesium is the next element in group 1, and it can be found below rubidium. You can accurately predict that it will have the lowest melting point, the highest density and the highest reactivity of all the elements in group 1.