Question

An atom of chlorine is represented by $_{17}^{37}Cl$. How many neutrons are in the nucleus of this atom?

Answer 1

The number of neutrons in an element can be determined by the atomic mass of the considered element. At first, we would find the atomic number of a given species which would give us the information about the number of electrons, and the protons carried by the species. After that we take the difference between the atomic mass of the element and the number of protons or electrons which would give the appropriate number of neutrons.
Complete answer:
Now we know that an element is divided into three components, namely, protons, neutrons and electrons. The species which carry negative charge and tend to revolve around the nucleus of the element or atom are termed as electrons. The positively charged species which are present inside the nucleus of the atom, are termed as the protons. And the species which are neutral in charge and are also present inside the nucleus are called the neutrons.
If we consider the species which is provided to us, it is chlorine whose group number is $17$ and so it is a p-block element, and also it has the atomic number $17$. This information tells us that the element contains the same number of electrons in it. Meaning it has $17$ electrons. We know that this element is electrically neutral so the number of electrons and protons would be equal. So, it is safe to say that the number of protons is $17$.
Now in order to determine the number of neutrons of the atom we would find out the atomic mass of the atom which is $37$, as it is given in the question. Now, we would be taking the difference of both the quantities, meaning the atomic mass along with the number of protons or electrons, and we get,
$37-17=20$
Hence, the number of neutrons in the atom $_{17}^{37}Cl$ is $20$.

Note: The number of neutrons in an element could differ from the number of protons and number of neutrons. The number of neutrons of different isotopes of the same element could also differ from each other. The sum of the number of protons and neutrons is also termed as the mass number.