Question

The electronic configurations of three elements X, Y and Z are $2,8;$ $2,8,7;$ and $2,8,2;$ respectively. Which of the following is correct?
(A) X is a metal
(B) Y is a metal
(C) Z is a non-metal
(D) Y is a non-metal and Z is a metal

Answer 1

Hint:Firstly we should be clear that what exactly is the electronic configuration. Now it is basically the distribution of electrons of an atom or molecule (or other physical structure) in atomic or molecular orbitals.

Complete answer:Firstly we should be aware with the question is regarding the field of electronic configuration for the element.
In the field of atomic physics and the quantum chemistry, the electron configuration is considered as the distribution of electrons of an atom or molecule (or other physical structure) in atomic or molecular orbitals.
Now we can say that the Electronic configurations are the ones that describe each electron as moving independently in an orbital, and also in an average field created by all other orbitals. Mathematically, we can say that the configurations are described by Slater determinants or configuration state functions.
Generally, we can say that metals have a lesser number of electrons in their outermost shell which can generally be a maximum of three electrons. So, we can say that from the given options of compounds Y cannot be a metal and X has a complete electronic configuration in the valence shell and is not a metal.
$$X-2,8;$$ is the electronic configuration of a noble gas (Ne) with a valency of $$0$$ .
$$Y-2,8,7;$$ is the electronic configuration of a non-metal or halogen (Cl) with a valency of $$1$$ .
$$Z-2,8,2;$$ is the electronic configuration of a metal (Mg) with a valency of $2$ .

Therefore the correct option would be option (D), Y is a non-metal and Z is a metal.

Note:According to the laws of quantum mechanics, for systems with only one electron, a level of energy is associated with each electron configuration and in certain conditions, electrons are able to move from one configuration to another by the emission or absorption of a quantum of energy, in the form of a photon.