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 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.
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.
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:
|Lithium||Decreases down the group||Increases down the group||Increases down the group|
|Sodium||Decreases down the group||Increases down the group||Increases down the group|
|Potassium||Decreases down the group||Increases down the group||Increases down the group|
|Rubidium||Decreases down the group||Increases down the group||Increases 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.