Some times the number comes before the name of the element ie 2Mg rather than ?

Question

the 2 after it and writen as subscript.?

i have asked this before and never really understood the answer i have only being doing chemistry for month the can you explain it with out the chemistry mumbo jumbo in simple terms please

Answer 1

It makes doing calculations easier, its used for a slightly higher than basic level.  During chemical equasions its sometimes neccesary to include 2 or more of the same molecule to be left with the end product.  It makes the whole 'what comes in must come out' thing work!

Answer 2

Here's my explanation:

If we are talking about the element being in a compound, we would for example write Na2SO4, but if we are talking about individual atoms or ions we would write 2N or 2Na+. For the reaction of sodium with sulfuric acid:

2Na + H2SO4 => Na2S + H2  {DO NOT TRY THIS AT HOME!!!}

Why is it H2 instead of 2H, you may ask. Because the hydrogen molecule consists of 2 atoms.

P.S. The above reaction is very dangerous.  

Answer 3

2Mg means two atoms, (or 'moles), of magnesium.

Mg2 would mean two atoms of Magnesium in the molecule.

Magnesium does not form diatomic molecules like the gasses, (O2, H2, N2, .....), so we write it as 2 Mg when that's what we want to talk about.

Answer 4

All it means is there are two molecules of the compound following the 2, as opposed to the subscripted 2 following an element that denotes the number of atoms of the element in a compound or equation.

2H2O means 2 molecules of water and that one molecule of water has 2 hydrogen atoms.

Answer 5

as subscript defines number of atoms in the molecules and as superscript or before it defines the number of molecules