Question: how come we can smell some gases and we cant see gases

Reka Nagy answered on 8 Nov 2016:

It’s all about the chemicals that make up certain gases – if a gas contains sulphur, or more precisely, hydrogen sulphide, for example, it will smell pretty bad, like rotten eggs.
We perceive smell when molecules enter our nose and bind to smell receptors there. If we do not have receptors for a specific chemical shape, we will not be able to smell it. Also, if we smell something for too long, we lose our ability to smell it for a while, because our brains will start considering this smell ‘normal’ and will start ignoring it, looking out for other, different smells instead.

We CAN see some gases – again, it depends on the chemicals that make them up. Chemicals are made of atoms, and atoms are made of a positively-charged core and is orbited by negatively charged electrons. Colour is produced when electrons move orbits around the core. The electrons of some atoms move around more than the electrons of others, so for example chlorine gas is yellowish-green ( https://goo.gl/mRv0Hv ) and Iodine vapour is a lovely purple ( https://goo.gl/BQoJi6 ).