Question

what is valency and atomicity explain in detail

Answer 1

Here are the basic definitions : 1) Valency : The electrons in the outermost shell of an atom are called valence electrons. But valency means the combining capacity of an element, basically it's the number of electrons that an atom can transfer to attain a noble gas config. For example : 1) Oxygen : Element 8; it has 6 electrons in outermost shells, but it needs two more to attain an octet/noble gas config. So it's valency is 8-6=2. 2) Phosporous: Element 15; it has 5 electrons in outermost shell but it needs three mroe to attain an octet. => Valency=8-5=3. 3) Sodium:Element 11; it has 1 electrons in outermost shell so it needs to give away one electron to attain octet. So the valency is 1. Basically, the valency for an atom with less than four electrons in outermost shell is the number of valence electrons whereas for more than four electrons, valency is 8-(number of valence electrons). This is only applicable for 20 elements though. Atomicity: It is simply the number of atoms of an element in a molecule or compound. Example:1) S molecule: Sulphur usually exists as S8, so the atomic of sulphur is 8. 2)C6H12O6: Atomicity of carbon is 6, oxygen is 6 and hydrogen is 12.