# How many neutrons are in calcium?

May 24, 2017

#### Answer:

$\text{Usually 20 neutrons............}$

#### Explanation:

Why $\text{usually.........?}$

Every calcium nucleus contains 20 positively charged, nucular particles, $\text{20 protons}$. This is what defines the nuclide as a calcium nucleus, i.e. $Z = 20$. However, the nucleus can contain varying numbers of neutrons. Most calcium nuclei (approx. 97%) contain $20$ neutrons.........to give the ""^40Ca isotope. There are much smaller percentages of the ""^42Ca and the ""^44Ca isotopes. The weighted average of all the isotopic masses gives the atomic mass reported on the Periodic Table, i.e. $40.1 \cdot g \cdot m o {l}^{-} 1$. Clear?