Quantum Numbers and Electronic Configuration: Chemistry Decoded
by Yuvi K - December 16, 2023
Quantum Numbers and Electronic Configuration: Chemistry Decoded
Quantum numbers are integral to the world of chemistry. In this article, we will be familiarizing ourselves with these numbers and exploring what role these play in the elecron configuration of atoms. By the time you reach the end of the article, you will have a crystal clear understanding of the significance of quantum numbers, as well as the electronic configuration of atoms.
What are Quantum Numbers?
Quantum numbers (Q.N) are a set of mathematical variables that can be used to denote the position, energy and momentum of an atom belonging to atomic orbital of an atom. They characterise the quantum state of an atom and can be calculated using Schrodinger Equation.
Quantum numbers for electrons are often indicated by four numbers, n, l, m and s. These are the four quantum numbers which can help to explain the energy and position of a single electron with respect to an atomic nucleus.
Four Quantum Numbers (Q.N):
- Principal Quantum Number (n):
It is used to represent the energy level and the size of orbitals in which the electrons are present in an atom. Its value must be greater than zero. The value of this quantum number is usually represented by letter n. Its values range from 1 to n, where n is the number of electrons in an atom. - Azimuthal quantum number (l):
It accounts for the shape of the orbitals in which the electrons are present. Its value can range from 0 to (n-1). The value of l is usually represented by a letter. The letters s, p, d, f stand for values 0,1,2,3 respectively and can be used to indicate the shape of orbitals. - Magnetic quantum number (m):
It helps to indicate the number of orbitals which can fit in a given energy level. Its value can range from -l to +l. That is, it has a value of -1 to +1 for l=1, -2 to +2 for l=2 and so on. - Spin quantum number (s):
It indicates the spin of electron. Its value can be +½ or -½. It is indicated usually by arrows ↑ or ↓. The spin quantum number is important for interpreting the magnetic properties of atoms.
Electron Configuration and Quantum Numbers
Electron configuration is the arrangement of electrons in an atom. It is the sequence of quantum numbers of electrons that tells us which orbital is occupied by an electron.
The Pauli exclusion principle states that no two electrons can occupy the same quantum state simultaneously, that is, no two electrons can have the same set of quantum numbers. Quantum numbers combined with the Aufbau principle, which states that electrons occupy lower energy levels first, can be used to find the electron configuration of an atom.
The Aufbau Principle:
The Aufbau principle (Aufbau = build up in German) states that electrons will fill the energy levels of an atom from the lowest energy level to the highest energy level. It can be used to find the electron configuration of an atom.
According to this principle, electrons will start to fill the available orbitals of the lowest energy level first. This process will continue until all orbitals of the lowest energy level are filled. Once the orbitals of the lowest energy levels are filled, electrons will start to fill the orbitals of the next-highest energy level and so on.
The quantum numbers associated with each orbital determine the energy level of that orbital. The principal quantum number (n) is the most important determinant of the energy level of an orbital. As the principal quantum number increases, the energy of the orbital increases.
Electron Configuration Example
Let us take an example of helium atom (He), which has two electrons. According to Aufbau principle, electrons will fill the lowest energy level first, i.e. 1s orbital.
electron configuration of Helium (He)
1s2
This denote that both electrons are present in 1s orbital. As this orbital is completely filled, we have the electron configuration of helium.
Summary:
Quantum numbers are essential for understanding the behavior of electrons in an atom. They help us to determine the energy and position of an electron with respect to the nucleus. The Aufbau principle states that electrons fill lower energy level orbitals first and quantum numbers help us to determine the energy level of an orbital. These quantum numbers combined with the Aufbau principle can be used to find the electron configuration of an atom.
In this article, we have explored the significance of quantum numbers and their role in electronic configuration. This in-depth knowledge of quantum numbers and their application will come in handy for chemistry students who wish to delve deeper into the world of the atom.
