I understand all you have written but suppose I want to find out how many grams in one atom of Nitrogen? Is it 14 divided by 6.02x10^23 ?

There are two ways of finding the mass of a single atom (well, they are bot the same, kinda)

you know that Mass = (Number of Moles) x (Relative Molecular Mass), from my first post (and from your classes, I hope)

Now, you know you have 1 atom...in moles, that is 1/(6.02x10²³), which leads to the mass being calculated as you stated, 14/(6.02x10²³)

Alternatively, you use the Atomic Mas Unit, u
An atom of ¹⁴N weighs 14u

the value of u is 1.66x10^-27kg (It's a Physics constant, hence the kg units)

But of course, that's just the same as 1 divided by the molar constant (taking grams and kg into account), so you're doing the same thing!

(in short, the answer to your question is "yes")

Mass = (Number of Moles) x (Relative Molecular Mass)

Number of atoms = number of moles x Avagadro's number.

You can use both of those, with some rearrangement, to work out the first 3 of your conversions.

Litres to moles.....1 mole of a perfect/ideal gas at room temperature and pressure occupies about 24 (23.6?) litres

A mole is just a number, which is 6.023x10^23 (Avogadro’s number) , This is how many atoms are in 12g of carbon. The periodic table shows the molecular weight of all the elements.

This molecular weight is just stating how much 6.023x10^23 atoms, or one mole, of the element weighs. For example the molecular weight of nitrogen is 14g meaning that one mole, or 6.023x10^23 atoms of nitrogen would weigh 14g.

If you have a molecule, for exam methane CH4, one mole would be the weight of one mole of carbon plus 4 moles of hydrogen which equals 16g.

1 Now for your questions, to convert grams to moles you work out how much one mole of the substance you are looking at would weigh (e.g. 16g for methane). You then just have to divide the weight you actually have, by how much one mole weighs. So if you have 1.6g of methane, divide that number by the weight of one mole, 16g, to give you the number of moles you actually have, 0.1 moles.

2 As I said a mole is just the number 6.023x10^23 , to convert moles to molecules or atom, just multiply the number of moles you have by 6.023x10^23

3. To convert grams to molecules/atom just work out haw many moles you have then times by 6.023x10^ 23 .

4. To convert from litters to moles you need to no the density of the substance you have, if the density is 1.2, it means that every cm cubed weighs 1.2g. If you had one litre of a substance with a density of 1.2, you would have 1000x 1.2 grams of the substance. Then you just have to convert from grams to moles as above.

Bit of a long reply, hope it helps though.