# Question #021e1

May 15, 2017

$36$ neutrons.

#### Explanation:

One way we have of differentiating between various nuclides of the same element is by writing the name of the element followed by a hyphen and the mass number of the nuclide.

In your case, you would have zinc-66, a nuclide of zinc that has a mass number equal to $66$.

Now, an atom's mass number, $A$, tells you the number of protons, which is given by the atomic number, $Z$, and neutrons present inside the atom's nucleus.

$\textcolor{b l u e}{\underline{\textcolor{b l a c k}{\text{mass number = no. of protons + no. of neutrons}}}}$

Alternatively, you can write

$A = Z + \text{no. of neutrons}$

Grab a Periodic Table and look for zinc, $\text{Zn}$. You'll find it located in period 4, group 12. Look at its element box and make a note of its atomic number.

As you can see, zinc has

$Z = 30$

You already know from the nuclide's isotope notation that

$A = 66$

This means that you have

$\textcolor{\mathrm{da} r k g r e e n}{\underline{\textcolor{b l a c k}{\text{no. of neutrons} = 66 - 30 = 36}}}$