Isotopes of hydrogenHydrogen is the lightest and simplest element in the universe. It’s also the most common—about 90% of the atoms in the universe are hydrogen! But what makes hydrogen so unique? One reason is that it usually has no neutrons at all.

Atoms are made up of three particles: protons, neutrons, and electrons. Protons and neutrons are found in the nucleus (the center of the atom), and electrons orbit around the outside. Most elements have both protons and neutrons in their nucleus—but hydrogen is different.

The most common form of hydrogen has:

●     1 proton

●     0 neutrons

●     1 electron

This form is called protium. It’s the simplest atom possible. But hydrogen can also exist in two other forms, called isotopes:

●     Deuterium has 1 proton and 1 neutron

●     Tritium has 1 proton and 2 neutrons
 

Even though these are still forms of hydrogen, they have different numbers of neutrons. Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons.

So, how many neutrons does hydrogen have?
In its most common form—zero. But depending on the isotope, it can have 1 or 2.

Fun Fact; Tritium, a rare form of hydrogen with 2 neutrons, is slightly radioactive and is used to glow in watch dials and emergency signs!