Question

Following Dalton’s theory, scientist were curious to know the answer of the question:

What makes the atoms of one element different from the atoms of another element?

Answer 1

Atoms of different elements differ in the number of protons in their nucleus. This number is called the atomic number (Z) and it decides the identity of an element. For example, hydrogen has 1 proton, helium has 2 and sodium has 11. Since an atom is neutral, the number of electrons also equals the number of protons, which further decides its chemical behaviour.