What are the different forms called in an element that has forms with different numbers of neutrons?

1 Answer
Jul 1, 2018

Answer:

You speak of isotopes....and let us consider one simple example....

Explanation:

As far as we know most matter in this universe is hydrogen... And this is composed atom with ONE defining proton in is nucleus, about which a single electron, of charge opposite to the proton, whizzes about. And we represent the most common isotope of this species as #""^1H#, #"protium"#...

The nuclear core CAN contain another massive particle, the neutron, and such an atom we would represent as #""^2H#, i.e. the deuterium isotope...the which has approx. 1% abundance. This is still hydrogen, (because #Z=1#), but it is TWICE as massive than garden variety hydrogen. And this is the #""^2H#, #"deuterium isotope"#. And the presence of another neutron in the nucleus gives #""^3H#, i.e. #"the tritium isotope..."#

If you look up the atomic masses on the Periodic Table, you find that most elements have non-integral atomic masses, given that they are calculated on the basis of an envelope of isotopes of DIFFERENT abundance...

e.g. iron metal... #5.845%; ""^54Fe;# #91.754%; ""^56Fe;# #2.119%, ""^57Fe;# #0.282%, ""^58Fe.# The weighted average of these isotopic masses gives the atomic mass we read on the Periodic Table, #Fe, 55.845(5)*g*mol^-1#..