Hydrogen

Hydrogen has a mass number of one and an atomic number of one.

 Hydrogen atoms, therefore, contain only one proton and one electron.

No neutrons? No wonder they’re so light!

NOTE:

As shown above, hydrogen has no neutrons.

The number of protons defines an element, because it’s the only thing that remains constant; everything else can change.

Electrons can be transferred from one atom to another through ionic bonding to make ions (remember the transfer being ironed onto the t-shirt?) and the number of neutrons can also be altered to form an isotope (‘ice on top’).

It is the number of protons that defines the name of the atom.