Question

If an atom has an atomic number of 15 and mass number of 31, how many protons, neutrons and electrons does the atom contain?

Answer 1

Hint: In order to calculate the number of neutrons, protons and electrons present in the nucleus of an atom, we must be knowing about the concepts such as the atomic number and the mass number of the atom. From this we can easily calculate the neutrons, electrons and protons present.

Complete answer:
First let us see what an atom is. All the matter is composed of tiny particles, which are called atoms. Atoms have many subatomic particles such as protons, neutrons, electrons, alpha and beta particles. An atom is made up of nucleus with the electrons revolving around it. The nucleus is made up of the protons and neutrons. The protons and neutrons together are called nucleons. Proton is one of the subatomic particles which has a positive charge. The neutron will be having a neutral charge. The electron will also have a charge which is negative.
Let us now understand about the atomic number. The total number of the electrons or protons present in the atoms are called the atomic number, which is represented by the symbol Z.
Now let us move onto the mass number. The total number of protons and neutrons together present in the nucleus of an atom will give the mass number, which is denoted by the symbol A.
Now let us move onto the given question. The atom which is having the atomic number of 15 and mass number of 31 is Phosphorus atom.
From the atomic number, we can calculate the number of protons and the number of electrons. As the atomic number is the total number of protons or electrons.
Number of protons of phosphorus atom = number of electrons of the phosphorus atom = 15.
we can calculate the number of neutrons from the mass number. We can subtract the number of protons of an atom from the mass number of that particular atom.
Number of neutrons of phosphorus atom = mass number of phosphorus atom – number of protons of the phosphorus atom
$Numberofneutronsofthephosphorusatom=31-15=16.$
Therefore, phosphorus atom will have
$$\begin{gathered} Numberofprotons=15 \\ Numberofelectrons=15 \\ Numberofneutrons=16. \end{gathered}$$

Note: We have to remember that all protons, neutrons and electrons will be having different charges.
- The charge of the proton is positive.
- The charge of a neutron is neutral.
- The charge of the electron is negative.