Question

How do you arrange the following sublevels in order of decreasing energy: $3s$, $3d$ and $3p$ ?

Answer 1

Atoms consist of electrons that revolve around the nucleus. Electrons are negatively charged particles that move in a circular motion while moving around the nucleus. Electrons’ revolution is restricted in particular orbits based on their energy levels.

Complete step-by-step answer:
Energy levels are defined as the fixed distances of electrons from the nucleus of an atom. They are also known as electron shells. Electrons cannot stay between the two energy levels. It has to move from one energy level to another. Atomic orbitals are defined as the mathematical functions that tell us about the wave nature of electrons. It exists around the nucleus of an atom.

There are four different types of orbitals – $s,p,d,f$ . The $s$ orbitals are spherically symmetric, in which the probability of finding the electron is equal in all directions. $p$ orbitals consist of two sections, which are known as lobes. $d$ orbitals have clover shape.

Electronic configuration is defined as distribution of electrons in an atomic orbital. It describes each electron as moving independently in an orbital with an average field generated by other orbitals. An electron shell shares the same principal quantum number $(n)$ that electrons may occupy and a subshell is defined as a common azimuthal quantum number $(l)$ within a shell.

In this question, we can notice that the sublevels are $s,p,d$ , which have the same number of orbitals and have the same amount of energy. According to the Aufbau rule, the ground state of an atom, electrons fill the atomic orbital of the lowest energy level before occupying a higher energy level. For example, $2s$ subshell is filled before $3s$ subshell. This increases the stability of electron configuration.

First, we will see the increasing order of sublevels. $1s\,2s\,2p\,3s\,3p\,4s\,3d\,4p$

Therefore, the highest energy orbital among the given options will be $3d$ and the lowest will be $3s$ , so, the decreasing order of sublevels on the basis of energy will be:
$3d>3p>3s$

Note:
i) According to the Hund’s rule, before the double occupation of any orbital, firstly each orbital in the subshell is singly occupied.
ii) According to the Aufbau rule, firstly the electrons will fill the lowest energy level and then it occupies a higher energy level.