Question

how can you efficiently determine the number of atoms in a sample of an element?

Answer 1

To calculate the number of atoms in a sample, we needto find how many moles of the element the sample contains. A mole is a unit chemists use. It's equal to Avogadro's number (6.02 X 10^23) of atoms. By definition, the weight of one mole of an element (its molar mass) is equal to its atomic weight in grams. The atomic weight for each element is on the periodic table right under the element's symbol. The atomic weight of carbon is 12 atomic mass units (amu), so the weight of one mole is 12 grams.  

OR

We use Avogadro calculation:

1 mole =6,02×1023particle

Every element have unique atomic mass (or atomic weight). If you want to calculate the number of atoms,

At first measure mass of the element

And then divide it by atomic mass, by doing this we will get value of element in mole.

Then just multiply by Avogadro’s number 6,02×1023 so you’ll get number of atoms.

EXAMPLE

How many oxygen atoms are there in a gas sample that weighs 20 grams?

Ans.The atomic weight of oxygen is 16, so one mole weighs 16 grams. The sample weighs 20 grams, which is equal to 1.25 moles. Therefore, the number of atoms is 7.53 x 10²³.