The Periodic Table (CIE IGCSE Chemistry)

• There are over 100 chemical elements which have been isolated and identified
  • 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
  • Elements are arranged on the periodic table in order of increasing atomic number
  • The table is arranged in vertical columns called groups and in rows called periods

The period number

• Periods are the horizontal rows that show the number of shells of electrons an atom has and are numbered from 1 - 7
• Elements in Period 2 have two electron shells, elements in Period 3 have three electron shells

The group number

• Groups are the vertical columns that show how many outer electrons each atom has
• They are numbered from 1-7 with a final group called Group 0 (instead of Group 8)
• 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 group number can help determine the charge that metal and non-metal ions form
• For metals, the group number corresponds to the number of electrons it will lose to achieve a full outer shell and the charge of the metal ion
  • Sodium is in Group 1, it will lose 1 electron and form an ion with a 1+ charge
  • Magnesium is in Group 2, it will lose 2 electrons and form an ion with a 2+ charge

• For non-metals in Group 7 and 6, they will gain 1 and 2 electrons respectively to gain a full outer shell 
  • E.g. non-metals in Group 7 gain 1 electron to form ions with a 1- charge
  • Non-metals in Group 6 gain 2 electrons to form ions with a 2- charge

The Periodic Table

All elements are arranged in the order of increasing atomic number from left to right