about the naming of covalent bond

hello every one! i am learning about covalent bond but i got some problems.IT is that i dont know how to name the formula of those molecules. Example,hydrogen sometimes place at back but sometimes placed at front .Can everyone help me ?


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there's probably some IUPAC nomenclature rules about this somewhere,
but generally........

in small molecules, you put the most electropostive element first

thus with hydrogen
LiH lithium hydride,
AlH3 aluminium hydrife,
CH4 methane
NH3 ammonia
but H2O oxygen
H2S hydrogen sulphide
and HF hydrogen fluoride

similarly you write NaCl, not ClNa...

(it's just a convention, there's no particular life-or-death reason for it)

with bigger molecules, you normally group the symbols to show the molecule's structure

so for instance ethanoic acid you'd usually write as CH3COOH
(which shows that there's a CH3 methyl group,
a C=O carbonyl group,
and an OH hydroxyl group in it)

it just makes it easier to recognise.

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