Isotopes

In a periodic table, there are two values that are given for each element.

The number on the top of an element is known as the atomic number and the number on the bottom is the atomic mass.

For example, sodium has an atomic number of 11 and an atomic mass of 23.

Atomic number - number of electrons and protons in the neutral of the element.

Atomic mass - Quantity of matter contained in an element.

When we are looking at isotopes. Isotopes are different versions of an element. The isotopes of an element have a varying number of neutrons in their nucleus.

First, you need to understand that only a change in proton number creates a new element. A change in electron or neutron number doesn't create a new element. So one element can have different versions that have a different number of neutrons.

For example, oxygen has 8 electrons and 8 protons, but it has different isotopes with a varying number of neutrons. Oxygen has three different isotopes. There is oxygen-16 which has 8 neutrons, oxygen-17 which has 9 neutrons, and oxygen-18 which has 10 neutrons.

A common question when it comes to isotopes is:

Do different isotopes have different chemical properties?

The answer is no, they don’t. The number of electrons and the exchange of electrons determines the chemical properties of an element. All isotopes in a neutral state have the same number of electrons, so they don't have varying chemical properties. The only difference between the isotopes would be in their atomic mass. This is because when there is an increase or decrease in neutron number the amount of matter in the atom will change which will affect the mass of the atom.

The atomic mass given to an element in the periodic table is known as the relative atomic mass. The relative atomic mass is like a relative average of all the different isotopes of an element. It is a relative average value because different isotopes are present in varying quantities in nature.