Octahedral coordination

linking of six legends which are present at the corners of an octahedron, e.g., SF₆ has a octahedral coordination about S.

Octahydrate

A crystalline compound containing eight molecules of water of crystallisation per molecule of compound.

Octavalent

Having a valence of eight

Omium ion

An ion formed by addition of a proton (H+) to a molecule. The hydromium ion (H₃O+)and ammonium ion (NH₄+) are examples.

Onium compounds

Groups of compounds containing cations of the type RxA+ which are analogous to ammonium compounds. Ions include phosphonium R4S+, oxonium R3O+, sulphonium R3S+, iodonium R2T+.

Open hearth process

Refers to a method of making steel by heating pig iron in an open-hearth furnace by burning a mixture of gas and air. Oxygen is injected through pipes to oxidise impurities and burn off carbon, and lime is used to form a slag.

Orbital

 it is defined as three dimensional space around the nucleus of an atom where there is maximum probability of finding an electron. It is different from an orbit which is a well defined path around the nucleus in which the electrons revolves. There could be a maximum of two electrons in any orbital and these two must have opposite spin.

Orbital moment

The component of the magnetic moment of an atom or ion resulting from the motion of the electron around the nucleus.

Orbital splitting
refers to the raising of the degeneracy of a series of orbitals of equivalent energy, e.g., by placing in a crystal field.