Question

What is the number of protons, neutrons, and electrons respectively in a zinc-70 ion which has the symbol $\text{Z}{{\text{n}}^{2+}}$?

Answer 1

Hint: The number of protons in an atom is its atomic number and the sum of the number of protons and neutrons is called its mass number or atomic mass. Neutral atoms possess the same number of protons and electrons but when an atom gains or loses one or more electrons, it is called an ion. If an atom loses 2 electrons, it will become a cation having +2 charge as superscript.

Complete answer:
An element can exist in more than one form and it was found that there is a relationship between different forms of the same element. These forms or atoms of the same element tend to possess the same number of protons but different numbers of neutrons and are called isotopes.
The number of protons is always the same in atoms of the same element. However, the number of neutrons can be different.
Since isotopes have the same number of protons but differ in the number of neutrons, so they have the same atomic number and different mass numbers. Different isotopes of an element generally show the same physical and chemical properties as they have the same numbers of protons and electrons.
Now, the atomic number of zinc is 30 which means that a neutral zinc atom contains 30 protons and 30 neutrons. And here we are talking about an isotope of zinc having a mass number of 70. So we can write –
\[\begin{align}
  & \text{No}\text{. of protons}=30 \\
 & \text{No}\text{. of protons}+\text{No}\text{. of neutrons}=70 \\
 & \therefore \text{No}\text{. of neutrons}=70-30=40 \\
\end{align}\]
Also, zinc-70 ion is having +2 charge, i.e., it contains 2 electrons less than that in a neutral atom.
\[\begin{align}
  & \text{No}\text{. of electrons in neutral atom}=30 \\
 & \text{Charge on the atom}=+2 \\
 & \therefore \text{No}\text{. of electrons in Z}{{\text{n}}^{2+}}=30-2=28 \\
\end{align}\]
Hence, there are 30 protons, 40 neutrons, and 28 electrons respectively.

Note:
Every isotope of elements is not stable as they possess an unfavorable number of protons and neutrons in the nucleus. Sometimes such a nucleus becomes very unstable and breaks down to a more stable form releasing some particles. This process is called radioactive decay and these isotopes are referred to as radioisotopes.