Need help with molecules.?

Question

How do you determine amount of molecules on a certain amount of grams of element?

Answer 1

First of all, look on your periodic table. Somewhere there should be a listing for atomic mass. Usually it's either at the very bottom of the square for that element or in a separate table. That is how much that atom weighs in amu, or atomic mass units. A molecule weighs as much as all the atoms in it put together.

A guy named Avogadro came up with a number called Avogadro's number (modest character, wasn't he?) or a mole. A mole is 6.023 * 10^23. There are exactly one mole of amus in a gram. Atoms are commonly measured in moles in the lab as well, since the actual number of atoms is usually way too high to work with conveniently.

So to answer your question, the number of atoms in a sample is (6.023 * 10^23 * the number of grams)/the atomic mass. The number of molecules is (6.023 * 10^23 * the number of grams)/the sum of the atomic masses of the component atoms (also called the molecular mass). But most of the time, amounts are reported in moles, and the number of moles is simply the number of grams/the atomic or molecular mass.

I hope that made sense to you.