Question

Valuable gemstones such as rubies and sapphire contain aluminium oxides along with the traces of transition metals as impurities.
State whether the given statement is true or false.
(A) True
(B) False

Answer 1

Hint: Gemstone is a piece of mineral crystal which is in cut and polished form used to make jewellery and other ornaments. When a small amount of other materials is present in a pure substance, it is termed as impurity.

Complete step by step answer:
Sapphire is a gemstone a variety of mineral corundum, an aluminium oxide. It occurs in many colours like yellow, orange, blue etc.
The only colour which sapphire cannot be is red – as red coloured corundum is called ruby.
Ruby is a crystalline form of aluminium oxide which is red due to the presence of chromium as an impurity.
Sapphires exhibit different colours in different light. The colour change is caused by the interaction of sapphire which absorbs specific wavelengths of light.
Presence of transition metals as impurities in the sapphire are responsible for colour change, as those metals have empty d-orbitals and when those electrons of the ground states get excited, it goes to one of these empty orbitals. Now, when they come back to the ground state, the electrons release their energy in the form of radiations. Now we know that the electromagnetic spectrum consists of different types of radiation, like the infrared, ultraviolet etc. One of these radiations is the visible region, which is visible to the human eye. So, the energy released by those electrons during the process of coming back to the ground state, falls on the visible region, hence we can see its colour.

Hence the given statement is true .

Note: The d-orbitals present in the transition metals, have space for the electrons which are being excited from the ground state to a higher excited state, and during the process of stabilisation of that excited electron, it comes down to the ground state releasing some radiations which falls on the visible region. So, the presence of transition metals as an impurity in gemstones, are responsible for the colour they impart.