Metals and Non-metals on the Periodic Table

Elements can be divided into two broad categories:

  • Metals
  • Non-metals

In the image below, you can see the location of metals and non-metals on the periodic table.

The periodic table with a line separating the non-metals from the metals.

  • The metals are on the left side of the separating line
  • The non-metals are on the right side of the separating line

There are also elements that display properties of both metals and non-metals. These elements are called metalloids or semi-metals.


Most of the elements in the periodic table are metals, and we can divide them into two broad categories:

  • Group 1 and 2 – Highly reactive metals
  • Transition metals (the middle section) – Less reactive metals

When metals react, they lose electrons to gain a full outer shell. This full outer shell will give them the same electronic structure as noble gases (group 0). For example, let’s look at the metal sodium (Na) reacting with chlorine:

A depicted sodium atom giving an electron to a chlorine atom. An arrow points to the positive sodium ion and the negative chlorine ion as a result of the electron transfer.

In this reaction, sodium, which is a metal, loses an electron to obtain a full outer shell. This forms a positively charged sodium ion (Na+). On the other hand, chlorine, which is a non-metal element, gains an electron to achieve a full outer electron shell. This forms a negatively charged chloride ion (Cl).

Let’s look at some more examples of metal reactions.

Example – group 1

Lithium is a group 1 metal which has 3 electrons in total and 1 electron in its outer shell. This makes it highly reactive, as it will readily lose its outer shell electron in a reaction.

When lithium reacts, it loses its outer shell electron, which results in a full outer shell with 2 electrons. However, this results in an imbalance, as the number of electrons and protons in the atom is no longer equal. Lithium originally had 3 electrons and 3 protons, so the overall charge was 0 (as protons have a positive charge and electrons have a negative charge).

After losing an electron, lithium has 3 protons in the nucleus but only 2 electrons, giving it an overall charge of +1. As lithium is charged, it is now an ion and we can draw it like this:

Lithium atom becoming a positive lithium ion due to the loss of an electron.

We write the charge in the top right corner.

Example – group 2

Another example of a highly reactive metal is beryllium, which is a group 2 metal. Beryllium starts out with 4 electrons in total and 2 electrons in its outer shell. During a reaction, beryllium loses two electrons in its outer shell to obtain a full outer shell.

Initially, beryllium had 4 electrons and 4 protons in the nucleus, so an overall charge of 0. However, after the reaction, beryllium lost two electrons, resulting in an overall charge of +2. This makes beryllium a positive ion, and we can draw it like this:

A Beryllium atom becoming a positive Beryllium ion due to the loss of 2 electrons.


In contrast to metals, non-metal elements have a large number of outer electrons. So atoms of non-metal elements will typically obtain a full outer shell by gaining electrons in some reactions. This is because non-metal elements have a tendency to gain electrons in order to achieve a full outer shell.

  • These reactions form negative ions

Therefore, the position of an element on the periodic table can provide insights into its reactivity.