# Why is it the percentage abundance is the reason why there are isotopes?

someone told me that isotopes exist because of the percentage abundance. . . why?

Isotopes are just atoms of the same element: same protons, but different amounts of neutrons. Percentage of abundance gives us the atomic mass unit which is an average. So, isotopes enable percentage abundance; percentage abundance enables AMU's
Isotopes exist, and thus there is percent abundance. Isotopes came first.
And isotope is an atom - the same kind of atom, that simply has a different number of neutrons. When we look at allllllllllll of the atoms of a certain element, if we weighed them, the mass of all of them would not necessarily be the mass of any of them, it would be something called a weighted average, which has to do with the amount of each atom present.

For example: let's make this simple. Let's say that nature has determined that we have an element X that has 4 isotopes. THe mass of one of the isotopes is 10 and 50% of allllll of the atoms of element X are this isotope.

The second isotope has a mass of 11 and 10% of alllllll of hte atoms of element X have this mass

The third isotope has a mass of 12 and 25% of allllllll of the atoms of element X have this mass.

The fourth isotope has a mass of 14 and 15% of allllll of the atoms of element X have this mass.

The average mass is due to the natural presence of each isotope.

% x mass = mass contribution

Summation of mass contributions of all naturally occurring isotopes = average mass (which is what is printed on the periodic table)

10 x 0.50 = 5
11 x 0.10 = 1.1
12 x 0.25 = 3
14 x 0.15 = 2.1

Average mass = 5 + 1.1. + 3 + 2.1 = 11.2

notice that the average mass is not equal to any of the actual masses of the individual isotopes (this happens more often than not - which is why none of the average masses are whole numbers on the periodic table).

Summary: isotopes are there - how much is due to nature/evolution/the development of this particular planet.

Isotopes and their percentages are set on this planet as they are - with each isotope came it's particular amount (just like everyone's arms and legs and head take up a general amount on a person's whole body - we never see a person with a head the size of their torso!! or arms as long as their legs!!)
an atom is defined by the number of protons it contains ie H 1
He 2 Li 3

however the number of nuetrons can vary within a type of element, making Isotopes

for example isotops of hydrogen are

protium 0 neutrons
deuterium 1 neutrons
tritium 2 neutrons

all three have different atomic weights, the atomic weight of hydrogen is an average that considers the % abundance.

isotopes do not exist because of the percentage abundance. The percent abundance is just an estimate to how much of one isotope exists in nature.

isotopes occur due to nuclear reactions/decay. These nuclear reactions are very small (involve one or a couple atoms) and occur all the time.

for example tritium can be formed when a high energy cosmic ray frees a neutron and accelerates it. If the fast neutron contacts a nitrogen atom a nuclear reaction occurs producing Carbon-12 and tritium.

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