The Periodic Table

In the early 1800s, the periodic table was arranged in a specific way. The elements in the periodic table were arranged according to their relative atomic masses and their chemical and physical properties.

Mendeleev helped to arrange some of the elements, he tended to put those with similar properties together. An example was when Mendeleev placed iodine after tellurium because it has similar properties to the other elements in that group.

  • Gaps were also left in the periodic table, so when other elements were discovered they were placed in their correct positions.

Let’s look at the basic structure of the periodic table of elements

There are around 100 different types of atoms which make up everything on Earth and the different types of atoms are called elements.

Elements are separated into metals and non-metals. The left side of the periodic table is where the metals are found, and the non-metals are found on the right side. The metals and non-metals are separated by the red zig zag line below.


The columns in the periodic table are called groups, the elements with the similar properties are found in the same groups. For example, all the elements in group 1 tend to have similar properties. This can include melting points, boiling points and how the elements react.

Also, the group number of the elements tells us how many electrons are present in the outer shell. For example, the elements in group 1 all have 1 electron in their outer shell.

It is important to know the major groups in the periodic table:

  • Group 1 elements are called the alkali metals – Not including hydrogen (which is a non-metal) , although it has similar properties to alkali metals)
  • Group 2 elements are called the alkali earth metals
  • Group 7 element are called the halogens
  • Group 8, otherwise called group 0 are called the noble gases
  • The central block of the periodic table are called the transition metals

The rows of the periodic table are called periods. Going from left to right of a period, we can observe certain patterns. The reactivity and properties of an element can be predicted using the periodic table.

The reactivity of group 1 elements increases as you go down the group. So, potassium is more reactive than lithium.