Valence Electron is an outer shell electron connected with the Atom. In atomic chemistry, it takes part in chemical bonding between atoms (only if the outer shell is open). These electrons can exist in the outermost shell of an atom, but in case of transition elements, they can also live in an inner shell.

The valence electron plays a vital role in atomic chemistry. It helps in defining the chemical properties of the element. The no. of valence electrons determines the reactivity and bonding capacity of an atom. As per the bonding theory, particles which have valence electrons share them with others to form chemical bonds. The higher the no. of valence electron results in a highly chemically reactive element.

So, to find the reactivity of an atom we need to determine the no. of valence electron. There are different ways to assess valence electrons for both Transitional Elements & Non-transitional elements.

For Non-Transition Elements-

In a perfect periodic table, you’ll see that each column is marked with numbers (from 1 to 18). As per the periodic table rule, The elements present in a column have the same no. of valence electron in their outermost shell.

Unfortunately, if your periodic table has not been assigned with numbers for each group, you can manually start numbering them from 1 to 18. For Example, above the column/group with H (Hydrogen) on the top, you have to write 1, and for the column/group starting with Be (Beryllium), you have to write 2 and so on.

As we’re continuing with non-transitional elements, we will ignore the transition elements (which are in the rectangular box, i.e. group 3 to 12) from the periodic table.

Okay, then. Now locate the element of which you want to find the valence electrons. If it’s a transitional element, then scroll down to the next part of this article. But if it’s non-transitional, then let’s find out with these step by step together.

For easy understanding, let’s pick one common element, Oxygen. The atomic no. of oxygen is 8. It is at the top of the group 16. In this method, we can find out the no. of valence electrons from the group number. The rule is, “The one’s place of the group number is the no. of a valence electron,”i.e.:

• Group 1: 1 Valence Electron
• Group 2: 2 Valence Electron
• Group 13: 3 Valence Electron
• Group 14: 4 Valence Electron
• Group 15: 5 Valence Electron
• Group 16: 6 Valence Electron
• Group 17: 7 Valence Electron
• Group 18: 8 Valence Electron {Except Helium (He), which has two valence electrons)

As Oxygen is in group 16, the no. of valence electron for Oxygen is 6.

For Transition Elements-

When it comes to valence electrons, Transition elements behave differently than non-transition elements. Explaining further, when particles got arranged in an atom, they got fit to a particular path for their orientation which is called orbitals. The particles that add in the last orbit, they show the nature of valence electron for sometimes. But after that, they don’t. Instead the electrons in the inner shell act like a valence electron. So the no of valence electron varies on how the element gets manipulated.

As we have done earlier, the group no. Can tell the no of valence electrons. But in the case of Transition Element, it shows a range of possible electron number. Those are:

• Group 3: 3 valence electrons
• Group 4: 2 to 4 valence electrons
• Group 5: 2 to 5 valence electrons
• Group 6: 2 to 6 valence electrons
• Group 7: 2 to 7 valence electrons
• Group 8: 2 or 3 valence electrons
• Group 9: 2 or 3 valence electrons
• Group 10: 2 or 3 valence electrons
• Group 11: 1 or 2 valence electrons
• Group 12: 2 valence electrons

I hope that this explanation has given you a clear idea for how to determine the valence electron of an atom.