CHEMISTRY

TOPIC:Atomic Model- [Quantum Numbers]

By Kingsley Idiagbor,B.Sc(Hons), PGDCs, NCE, MNSM

There are four quantum numbers to which the position of an electron can be determined. These are listed as follows:

• Principal quantum number;
• Azimuthal quantum number (sometimes known as subsidiary quantum number);
• Magnetic quantum number and
• Electron spin or spin quantum number

Principal quantum number

This refers to the various energy levels in the atom.  It is denoted by n and has to do with the energy that electrons possess due to their distance from the nucleus.  There is a certain number of electrons, which can be found in a particular energy level. This is determined by the expression, 2n² where n is the principal quantum number.

Azimuthal quantum number

Azimuthal quantum number has to do with the energy sub-levels that exist in each electron shell.

These energy sub-levels are known as orbitals.
Orbital is defined as the region or area in the atom where there is a high probability of finding an electron. The four orbital types are sharp (s), principal (p), diffuse (d) and fundamental (f), i.e. s-orbital; p-orbital; d-orbital and f-orbital. Azimuthal quantum number is denoted by l and has integral value of (n-1). The table below shows the number of  electrons in each orbital

Magnetic quantum number Magnetic quantum number shows the number of orbitals in each energy level as also depicted in the above table. It is denoted by m and has integral values ranging from +l through 0 (zero) to -l.

Two electrons may have the same charge, size, mass and even the same angular momentum. However, they cannot share the same electron spin. An orbital can only accommodates two electrons at a time, which spin on their axes in opposite direction. Their spins are denoted by the letter, s and can have the value of either +½ for those electrons with clockwise moments and   -½ for the set of electrons with anti-clockwise spin.

1. Define orbital

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