Calculate the Number of Electrons

How to Calculate the Number of Electrons?

For calculating the number of electrons in an atom, atomic mass and atomic number must be known of the element. The number of electrons is equivalent to the number of protons. Atomic mass represents the sum of protons and neutrons (as they are the ones that contribute significantly to the mass of the element)  whereas the atomic number represents the number of protons. 

Here A represents the atomic mass also known as mass number.

Z represents the atomic number.

And X represents the element. 

Example: Na has an atomic number of 11. Hence, it has 11 electrons

For calculating the number of electrons in a compound, the following steps must be followed:

Obtain the atomic numbers of the elements in the compound using the periodic table.

Then multiply the atomic number with the number of elements of this type present in the molecule. Repeat for all the elements present in the molecule and add it. Let’s refer to this calculated number as M.

Subtract the charge value from M if the charge is positive. If the charge is negative, add the charge value to the M.

Example:- HCO3– 

The atomic number of H is 1, C is 6 and O is 8. 

Summation Number of element present of same type multiplied with atomic number is 

(1×1)+(1×6)+(3×8) = 31

Since the charge value is 1 and negative, we will add 1 to 31 to obtain 32.

The number of electrons in  HCO3– is 32.