The Periodic Table (Cambridge (CIE) IGCSE Combined Science): Revision Note

The Periodic table

• 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 arrangement places elements with similar properties in the same columns

• The table is arranged:

  • In vertical columns called groups

  • In rows called periods

The period number

• Periods are the horizontal rows on the Periodic Table

• Periods are numbered from 1–7

• The period number shows the number of shells of electrons an atom has

• For example:

  • Elements in Period 2 have two electron shells

  • Elements in Period 3 have three electron shells

The group number

• Groups are the vertical columns on the Periodic Table

• They are numbered in roman numerals from I (1) to VIII (8)

• The group number shows how many electrons are in the outermost shell of the atom

• For example:

  • Group 4 elements have atoms with 4 electrons in the outermost shell

  • Group 6 elements have atoms with 6 electrons in the outermost shell

The Periodic Table

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