�鶹Լ��

The periodic table brings order to information about the chemical elements. It helps chemists to understand why elements react as they do.

There are more than 100 elements which are arranged in the periodic table and each is represented by a symbol. A section of the periodic table is shown below which illustrates how the elements are arranged.

The gives more information.

The chemical elements are arranged in order of increasing atomic number.

The horizontal rows are called periods and the vertical columns are called groups.

Elements in the same group have similar chemical properties. This is because they have the same number of outer electrons and the same valency.

An example of a group in the periodic table is the alkali metal group. This video clip shows some of the reactions that occur with this group.