Question

An atom of calcium has 20 protons, how many electrons does it have?

Answer 1

Hint: The atomic number of an atom i.e. the number of electrons present in that very atom or the element depends upon the number of protons present in that very atom or element. Now with the help of this you can easily answer the given statement accordingly.

Complete answer:
Calcium is a metal which belongs to the s-block elements of the periodic table and comes under the category of the alkaline earth metals.
It lies in the 2nd group and 4th period of the periodic table.
It has an atomic number as 20 and the mass number as 40. It has the electronic configuration as: ${{[Ar]}^{18}}4{{s}^{2}}$.
Now considering the statement as-
The number of electrons present in an atom i.e. its atomic number is always equal to the number of the protons present in the nucleus so that the atom as a whole is electrically neutral.
And The electrons which are present in the outermost valence shell of an atom are called the valence electrons.
So, as we know that there are 20 protons in the calcium atom, thus, the number of electrons in the calcium atom are also 20 and hence its atomic number is 20.

Note:
Calcium being a metal has two electrons in its outermost shell and has a strong tendency to lose these two electrons from its outermost valence shell to acquire the stable electronic configuration of the nearest noble gas.