Question

There are two stable isotopes of nitrogen, $^{14}N$ and ${^{15}}N.$ How many protons and neutrons does each isotope have?

Answer 1

In order to solve this question, we should know that atomic number of an atom represents its number of protons whereas the mass number of an atom represents sum of number of protons and number of neutrons so, here we will compare the mass number and atomic number of each isotope and then figure out number of proton and number of neutrons in each isotope of nitrogen atom.

Complete step by step answer:
Since, An atom X is always represented as ${}_Z^AX$ where A represents atomic mass and Z represents atomic number. And Isotopes are those pairs of elements which have the same atomic number Z but different mass number A. According to the question, we have two isotopes of nitrogen atom whose atomic number is $Z = 7$ so, atomic number remain same for isotopes and atomic number is number of protons in an atom hence, number of proton in each isotope $^{14}N$ and ${^{15}}N$ are $7.$

Now, mass number for isotope $^{14}N$ is $14$ let us assume number of neutrons are $n$ the mass number is sum of number of protons which are $7$ and number of neutron n so, we have
$14 = 7 + n$
$\Rightarrow n = 7$ number of neutrons in isotope $^{14}N$. Similarly for isotope $^{15}N$ is $14$ let us assume number of neutrons are n’ the mass number is sum of number of protons which are $7$ and number of neutron n’ so, we have
$15 = 7 + n'$
$\therefore n' = 8$

Hence, the number of protons in isotopes $^{14}N$ and ${^{15}}N$ are $7.$ and number of neutrons are $7$ and $8$ respectively.

Note: It should be remembered that, only when atomic number is same for two elements then only they are said to be isotopes, don’t confuse it with isobars which are elements which have the same mass number but different atomic number and the number of electrons are always equal to that of the number of protons in an neutral atom.