Question

The notation for an isotope of sodium $${}_{11}^{23}Na$$. Which row gives the composition of a neutral atom of this isotope of sodium?

	Number of protons	number of neutrons	number of electrons
A	11	12	11
B	11	12	12
C	11	23	11
D	12	11	12

(A) A
(B) B
(C) C
(D) D

Answer 1

Hint: In order to find the Number of protons, number of neutrons and number of electrons present in the neutral sodium atom, we must be able to determine the mass number and atomic number from $${}_{11}^{23}Na$$. After determining the mass number and atomic number, we can calculate the number of protons, number of neutrons and number of electrons present in the sodium molecule from that value.

Complete step by step answer:
- From the question we can see that sodium $${}_{11}^{23}Na$$ is having an atomic number Z = 11 and mass number A = 23. What is a mass number and what is an atomic number? Mass number is defined as the sum of the number of protons and number of the neutrons present in the nuclei. It is denoted by A. Atomic number is defined as the number protons or number of electrons present in the atom. It is denoted by Z.
- Since it is given that $${}_{11}^{23}Na$$ is a neutral atom, then the number of protons and electrons will be equal.
- Therefore, number of protons = number of electrons=atomic number = 11.
From the mass number given, we can calculate the number of neutrons present in the atom.
As we know mass number is the sum of protons and neutrons, therefore subtracting the number of protons from the mass number, it will give the number of neutrons present.
Mass number = 23
Number of protons = 11
Number of neutrons = Mass number - number of protons
Number of neutrons = 23 - 11 = 12.
Therefore, Number of protons, number of neutrons and number of electrons in the neutral sodium atom are equal to 11, 12 and 11 respectively.
So, the correct answer is “Option A”.

Additional information: Dalton in his theory said that atoms are tiny and indivisible particles which cannot be divided into any further. It was later discovered that atoms can have subatomic particles such as protons, neutrons, electrons, alpha particles, beta particles, etc. Among these protons, neutrons and electrons are fundamental particles of an atom.

Note: Number of protons and number electrons present in an atom will not be equal at all times. It is possible only when the atom present is a neutral atom. When the number of protons present in an atom is greater compared to the number of electrons, then the atom is said to be a cation. When the number of electrons present is greater than protons, then the atom is said to be an anion.