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Atomic Orbitals

Atomic Orbitals Definition

Orbit is the definite path of an electron that moves around the nucleus in an atom. This is similar to a planet, moves around the sun. Orbitals are the space or region around the nucleus where the electron are calculated to be present. So orbits and orbitals have totally different meanings.

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Shapes of orbitals

Different shapes of orbitals are drawn depending on the possibility of finding electrons around the nucleus. These are s, p, d and f. The shapes of these orbitals are discussed below:

s-orbitals

The s-orbitals are solid spherical shape around the nucleus. When principal quantum number n = 1 and azimuthal quantum number l = 0, that is 1s orbital which is closest to the nucleus. When n = 2 and l = 0 , i.e 2s orbital which contains one node. When n = 3 and l = 0, i.e 3s orbital which contains two nodes. The pictorial representation of these orbitals are shown below:

By CK-12 Foundation (File:High School Chemistry.pdf, page 265) [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

So we can say that the s orbitals are always spherical regardless of the principal quantum number, regardless of size, regardless of the number of nodes they contain.

 

p-orbitals

The p-orbitals are dumb-bell shape contains two lobes just like two identical balloons tied together. The two lobes stay away from each other along the axial line. When n = 1, there are no p-orbitals, it has only s-orbital. When n = 2 and l = 1, the magnetic quantum number m = +1, 0, -1. Thus three dumb-bell shape p-orbitals are found pointing towards the three axes x, y and z which are perpendicular to each other. These three orbitals are named as px, py and pz. The nodal plane is the plane where there are no possibility of finding any electrons. The nodal planes of px, py, pz are yz, xz and xy respectively.

By CK-12 Foundation (File:High School Chemistry.pdf, page 268) [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

d-orbitals

The d-orbitals have different shapes and these are only available when principal quantum number n = 3 or more. When n = 3, l = 2, then m = +2, +1, 0, +1 and +2. That means five d-orbitals are available in an atom. The directions, names and the shapes of these orbitals are as follows:

By Reshadet.sherifli (Own work) [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)], via Wikimedia Commons

 

f-orbitals

The f-orbitals also have different shapes and these are only available when principal quantum number n = 4 or more. When n = 4, l = 3, then m = +3, +2, +1, 0, +1, +2 and +3. That means seven d-orbitals are available in an atom. The directions, names and the shapes of these orbitals are as follows:

By Ángel Terrón, Ángel García-Raso y Miquel Barceló-Oliver [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

Electron distribution in orbitals

s-orbitals

Number of maximum electrons that each s-orbital can hold is two regardless of the number of principal quantum number (n). Such as 1s2, 2s2, 3s2 etc. We need to recall that the spin of these two electrons must be opposite.

p-orbitals

Each p-orbital can posses maximum of two electrons each that means six for all three p-orbitals. We can write that either 2p6 or 2px2 2py2 2pz2. The spin of each of these orbitals must be opposite.

d and f-orbitals

The total number of electrons in d-orbitals and f-orbitals are ten and fourteen respectively. Here maximum two electrons can occupy in each of these d or f-orbitals.

Spin quantum number

Spin of these two electrons in each orbitals will be always in opposite direction. Following image shows the maximum electron distribution in each orbitals:

 

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