Question

How to calculate the number of electrons?

Answer 1

Hint: Before answering this question, we should know that the atomic number is given by the total number of protons present in the nucleus of an atom. It is represented by Z. The element has atoms that consist of the same number of protons and have the same atomic number. Different elements have atoms that have the same atomic number. For example, The atomic number of carbon is 6 whereas the atomic number of oxygen is 8.

Complete answer:
The outermost subatomic particle of an atom is known as an electron. These electrons are negatively charged in nature and they revolve around the nucleus in an atomic orbit. These outer electrons are also termed as valence electrons of an element. Now, looking into the inner side of the nucleus where most of an element lies, that is protons and neutrons. Protons are stable and positively charged subatomic particles whereas neutrons possess neutral charge. Protons and neutrons have almost the same mass i.e $1.67\times {{10}^{-24}}$grams whereas electrons have much lesser mass compared to protons and neutrons i.e $9.1\times {{10}^{-28}}$.
As we know, the number of protons in a nucleus of the atom is equal to the atomic number (Z).
The number of electrons in an atom is equal to the number of protons.
Therefore, Atomic Number (Z) = Number of electrons = number of protons.

Note:
Mass number
The mass number of an atom is a combination of the number of protons and neutrons. It is represented by A. Nucleons is the term used to represent both protons and neutrons. Carbon has 6 protons and 6 neutrons, The mass number of it is 12. The number of neutrons can vary whereas the number of protons remains the same. The weight of an electron is equal to 0 which makes the atomic mass of an atom the same as of mass number. Atoms that are of the same element can have a different number of electrons which are called ions and a different number of neutrons that are isotopes.
Mass number = no. of protons + no. of neutrons, Now with the help of this formula we can easily solve the question.