Question

How many neutrons and protons does a typical neutral atom of phosphorus have?

Answer 1

Hint For an atom Atomic number (${\text{Z}}$) is always equal to the number of electrons or number of protons and Atomic mass (${\text{A}}$) is equal to the sum of the number of neutrons and protons.

Complete step by step solution:
Phosphorous is placed at the ‘V A’ group of the p - block in the periodic table and it is denoted as ${}_{{\text{15}}}^{{\text{31}}}{\text{P}}$.
-Upper quantity describes the atomic mass of the atom which is equal to $31$ and lower quantity describes the atomic number of that atom which is equal to $15$.
-Relation between atomic number, electrons and protons are described as follow:
Atomic number (${\text{Z}}$) = No. of electrons = No. of protons
From above relation it is clear that, number of electrons which are present outside the nucleus in the orbital of phosphorus atom is equal to $15$ and number of protons which are present inside the nucleus is also equal to $15$, because the atomic number (${\text{Z}}$) of phosphorous is $15$.
-Relation between atomic mass, protons and neutrons are described as follow:
Atomic mass (${\text{A}}$) = No. of protons + No. of neutrons
It is given that, atomic mass of phosphorus = $31$
And also we know that number of protons in phosphorus = $15$
So, number of neutrons = Atomic mass (${\text{A}}$) - No. of protons
No. of neutrons = $31 - 15 = 16$.

Hence $16$ neutrons and $15$ protons are present in the phosphorus atom.

Note: Here some of you may count the number of electrons always equal to the atomic number of that atom, which is not always correct because if an atom present in the form of ion then the number of electrons are not equal to the atomic number of that atom.