Question

An element X has atomic number 20 and it has mass number 40 a)write the electronic configuration of the element
b) state the valency of the element
c) calculate the number of neutrons in it

Answer 1

For element X,

Z=20

A=40

a). 1s2 2s2 2p6 3s2 3p6 4s2

b). The valency is 2 (no. of electrons in outermost shell is 2)

c). A(mass number) = Z(no. of protons) + no. of neutrons

    no. of neutrons=A-Z

                              =40-20

                              =20