The periodic table

This lesson covers: 

  1. The organisation of the periodic table
  2. Properties of different groups of elements
  3. Using the periodic table to predict reactivity

Properties of elements

Diagram of the periodic table highlighting periods and groups.

The periodic table is a table of all the chemical elements.


  • In 1869, Dmitri Mendeleev organised the elements into a table ordered by increasing atomic weight.
  • Mendeleev noticed that elements with similar chemical and physical properties occurred at regular intervals.
  • He arranged the elements into a table with:
  1. Horizontal rows called periods.
  2. Vertical columns called groups.

Groups of elements

Diagram of the periodic table showing groups, periods, metals, and non-metals.

The table organises elements into periods and groups based on properties:

  • Periods - The 7 horizontal rows. Properties of elements change gradually moving down each period.
  • Groups - The 18 vertical columns. Properties of elements in the same group are similar.
  • Metals - Found on the left and in the middle of the periodic table.
  • Non-metals - Found on the right side of the periodic table.

Predicting reactivity

The position of elements in groups gives clues about how reactive they are.

Group 1 - The alkali metals

Periodic table highlighting Group 1 alkali metals, Group 7 halogens, and Group 0 noble gases.
  • Group 1 elements are on the far left side of the periodic table
  • They are the most reactive metals.
  • Their reactivity increases moving down the group.

Group 7 - The halogens

Periodic table with group 1 alkali metals, group 7 halogens, and group 0 noble gases highlighted.
  • Group 7 elements are on the far right side of the periodic table
  • They are reactive non-metals.
  • Their reactivity increases moving up the group.

Group 0 - The noble gases

Periodic table highlighting Group 1 alkali metals, Group 7 halogens, and Group 0 noble gases.
  • Group 0 elements are on the far right side of the periodic table
  • They are very unreactive.
  • They have a stable outer shell of electrons.