The Periodic Table (WJEC GCSE Chemistry: Combined Science)

• 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 Periodic Table

The Periodic Table is arranged in groups (columns) and periods (rows)

• 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

The Periodic Table showing the location of metals and non-metals

The metallic character diminishes moving left to right across the Periodic Table