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

Question

Peyton Adams · Accepted Answer

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

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#..

Olivia Anton · Answer

undefined Isotopes are distinct forms of an element with different neutron counts.