Electrons and groups

A section of the periodic table. Moving across period two, elements have the electronic structure 2.1 to 2.8. Moving down group two, elements have electronic structure 2.2, 2.8.2 and section of the periodic table

Columns in the periodic table – groups

  • The vertical columns in the periodic table are called groups.
  • The elements in any one vertical column are in the same group.
  • The groups are numbered from left to right.
  • Elements in the same group have similar chemical properties.
  • The number of electrons in the outer shell of all the elements in a group is the same as the group number.


  • All the Group 1 elements – lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs) and francium (Fr) – have one electron in the outer shell.
  • The Group 7 elements – fluorine (F), chlorine (Cl), bromine (Br), iodine (I) and astatine (At) – have seven electrons in the outer shell.
  • Group 0 elements – helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) and radon (Rn) – have full outer shells. (Group 0 is sometimes called Group 8).

Rows in the periodic table – periods

Elements in the same horizontal row are in the same period. The periods are numbered from top to bottom.

The period number is the same as the number of occupied electron shells.

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