The Periodic Table (WJEC GCSE Chemistry)

There are over 100 chemical elements which have been isolated and identified

Elements are arranged on the periodic table in order of increasing atomic number

• Each element has one proton more than the element preceding it

• This is done so that elements end up in columns with other elements which have similar properties

The table is arranged in vertical columns called groups and in rows called periods

• Period: These are the horizontal rows that show the number of shells of electrons an atom has and are numbered from 1 - 7

• E.g. elements in Period 2 have two electron shells, elements in Period 3 have three electron shells

Group: These are the vertical columns that show how many outer electrons each atom has and are numbered from 1 – 7, with a final group called Group 0 (instead of Group 8)

• E.g. Group 4 elements have atoms with 4 electrons in the outermost shell, Group 6 elements have atoms with 6 electrons in the outermost shell and so on

The elements can be divided into two broad types: metals and non-metals

Atoms of different elements which do not have a full outer shell of electrons, can try to achieve a full outer shell by gaining or losing electrons in chemical reactions

Elements that react by losing electrons to form positive ions are metals

• Metals are located on the left and centre of the Periodic Table 

Elements that do not form positive ions are non-metals; this includes elements that react by gaining electrons to form negative ions and Group 0 elements

• Non-metals are located on the right hand side of the Periodic Table

Most of the elements are metals and a small number of elements display properties of both types

• These elements are called metalloids or semi-metals

The metallic character of the elements decreases as you move across a period on the periodic table, from left to right, and it increases as you move down a group

This trend occurs due to atoms more readily accepting electrons to fill their valence shells