What is the difference between an atom and isotope?

1 Answer


Isotopes are different versions of atoms of the same element.


Hydrogen comes in three versions.

Each version of hydrogen has 1 proton - this is why hydrogen has the atomic number 1.

All versions of hydrogen atoms have 1 electron in their neutral state. The number of electrons and protons are always the same in neutral (no charge) particles.

So what is the difference? The difference is in how many neutrons are found in the nucleus of the three versions.

H-1 has a mass number of 1 because it has 1 proton
(1 + 0 = 1)

H-2 has a mass number of 2 because it has 1 proton and 1 neutron
(1 + 1 = 2

H-3 has a mass number of 3 because it has 1 proton and 2 neutrons
(1 + 2 = 3)

The mass of a proton and a neutron are each 1 amu . Technically the mass of a proton is slightly different than the mass of a neutron, but you can ignore the tiny difference most of the time.

Here are a couple videos to help with this concept.

Video from: Noel Pauller

Video from: Noel Pauller

Hope this helps!