Question

An atom of aluminum has an atomic number of 13 and a mass number of 27. How many neutrons does it have?

Answer 1

Hint: An atom comprises a nucleus having neutrons and protons which are surrounded by electrons in orbits. Number of protons (atomic number i.e. ‘ $Z$ ’) can be considered to be equal to the total number of electrons in a neutral atom. The summation of the number of neutrons and number of protons equals the mass number of an atom (denoted as’ $M$ ’). Thus, the number of neutrons = $M-Z$ .

Complete answer:
In the given question, we know the value of mass number ($M$) of the atom of Aluminium which is mentioned below:
 $$\begin{gathered} M=27 \\ Z=13 \end{gathered}$$
We already know that:
 $Massnumber=numberofprotons+numberofneutrons$
And we know that the atomic number is equal to the number of protons which means that:
 $numberofprotons=8$
In case of neutral atom, number of electrons is equal to the number of protons so:
 $numberof\text{ electr}ons=8$
Thus, the number of neutrons in Aluminum atom can be obtained by subtracting the number of protons from the mass number i.e. $M-Z$ = $27-13=14$
Hence, an atom of aluminum having an atomic number of 13 and a mass number of 27 has 14 neutrons.

Note:
Each atom of a given element has the similar number of protons while atoms of distinct elements possess distinct numbers of protons. An atom consists of the same number of protons as well as electrons. As protons as well as electrons possess equal and opposite electrical charges, atoms have no overall electrical charge (i.e. neutral).