# What is the isotopic distribution of gallium metal?

Nov 28, 2017

Well what are the common gallium isotopes?

#### Explanation:

This site reports two common gallium isotopes, ""^69Ga, with 60.1% abundance, and ""^71Ga, with 39.9% abundance.

Now for gallium, $Z = 31$, i.e. in each and every gallium nucleus there are 31 massive, positively charged particles; this is what defines the element as gallium. And so in ""^69Ga, there must be $69 - 31 = 38 \cdot \text{neutrons}$....and in ""^71Ga, there must be $71 - 31 = 40 \cdot \text{neutrons}$.... The protons and the neutrons constitute most of the element's mass...

Nov 28, 2017

There are different isotopes of Gallium, all of which have a different amount of neutrons.

#### Explanation:

The problem is that there are multiple isotopes of Gallium. What this means is that there are Gallium atoms with different amounts of neutrons.

You have to first figure out which isotope of Gallium you want to analyze before trying to calculate the amount of neutrons.

If we decide to pick the most abundant isotope, it is ""^69Ga. Then we can subtract the atomic number, $31$, to get that there are $38$ neutrons.

The reason you might see a single number for an atomic mass of an element in a periodic table for example, is because those have averaged out the atomic masses of all the isotopes depending on how abundant they are. If the mass contains decimals, this is a big clue that it is not an atomic mass of a single isotope.