# How would you give the nuclear symbol for the isotope of gallium, Ga, that contains 40 neutrons per atom?

Oct 26, 2015

$\text{_31^71"Ga}$

#### Explanation:

In order to write the nuclear symbol of an isotope $\text{X}$, you need to know two things

• its atomic number - the number of protons it has in its nucleus
• its mass number - the numbe of protons and neutrons it has in its nucleus

In your case, you have to determine what the nuclear symbol will be for an isotope of gallium that contains $40$ neutrons in its nucleus.

The first thing to do here is take a look at a periodic table and make a note of gallium's atomic number.

Gallium is located in period 4, group 13 of the periodic table, and has an atomic number equal to $31$.

Since this isotope also has $40$ neutrons in its nucleus, it follows that its mass number will be

$\textcolor{b l u e}{\text{mass number" = A = "no. of protons" + "no. of neutrons}}$

$A = 31 + 40 = 71$

Now, nuclear symbol notation must follow these rules

In your case, $A = 71$ and $Z = 31$, so you have

$\text{_31^71"Ga} \to$ gallium-71