Why does the normal hydrogen atom lack a neutron

[abodunrine]

why is hydrogen the only element in the periodic table that lacks a neutron?

 

[mfb]

Two or more protons without any neutrons are not stable - their electrostatic repulsion is larger than the nuclear force. With an additional neutron, the nuclear force is stronger (and the electromagnetic force a bit weaker), and 3He is stable.

 

[mathman]

why is hydrogen the only element in the periodic table that lacks a neutron?

Right after the big bang the only nucleons were free protons and neutrons (which decay into protons). Nuclear fusion started to take place resulting in a lot of helium nuclei plus a small amount of other light nuclei, deuterons and Lithium nuclei. The net result was that the universe (after cooling down enough to form atoms) was about 75% H1 and 25% He4 and trace amounts of the others. The rest of the elements got created in stars and supernovae. However most of the universe is still H1 and He4.