Question

An atom of an element contains $29$ electrons and $35$ neutrons. Deduce
(i) the number of protons and
(ii) the electronic configuration of the element

Answer 1

In the ground state of an atom of an element, the number of electrons and the number of protons remain the same, in order to maintain the neutrality of the atom. The number of neutrons in an atom is equal to the difference of mass number and atomic number of the element.

Complete answer:
The number of electrons in the ground state of an atom is equal to its atomic number. The mass number of an element is defined as the total number of nucleons present in the nucleus of an element. The nucleons comprise of both neutrons and protons.
Thus, for an element, say X, the atomic number (Z) and mass number (A) can be represented symbolically as ${}^A{X_Z}$ or ${}_Z^AX$ .
(i) As per the question, the number of electrons = $29$
The number of neutrons = $35$
Hence, the number of protons = $29$
(ii) Now, we have to look for the electronic configuration of the element. The electronic configuration is defined as the number of electrons distributed in the various atomic orbitals of the element. As per the question, the total number of electrons in the ground state of the provided element is $29$, which means that the atomic number of the element is also $29$. Thus, the element is identified as copper ($Cu$ ) and the electronic configuration is:
$Cu = 1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}4{s^2}3{d^9}$

Note:
With the knowledge of the total number of electrons of an element, the electronic configuration and the total number of protons can be calculated. The term ‘ground state’ is mentioned in order to explain the term atomic number of the element without any loss or gain of an electron in it.