## Calculating the number of atoms

Bryan Ramirez 2C
Posts: 2
Joined: Fri Sep 28, 2018 12:17 am

### Calculating the number of atoms

If given only the mass of a sample in grams how would one go about finding the total number of atoms within the given sample?

KatrinaPho_2I
Posts: 60
Joined: Fri Sep 28, 2018 12:28 am

### Re: Calculating the number of atoms

To go from grams to atoms, you have to do grams -> moles -> atoms. For grams -> moles, simply divide the mass (g) of the sample by its molar mass (g/mol). For moles -> atoms, multiply the # of moles * 6.022x10^23 (Avogadro's number). The final answer will be the # of atoms in the given sample.

Joonsoo Kim 4L
Posts: 61
Joined: Fri Sep 28, 2018 12:29 am

### Re: Calculating the number of atoms

Think about the units of what you have and what you need, and then you can then identify which conversions you can use to get from point A to point B. For instance:

You have the mass (and I would assume you have the identity of the substance as well)
You need no. atoms

If you have the mass of a sample and its identity, it's generally always a good idea to convert that mass into moles. Molar mass is (g/mole), and since you have the mass of the sample, divide g/(g/mole) and the "g" unit will cancel out, leaving you with just moles.

Now, you have the number of moles in the sample, and you can convert this to atoms using Avogadro's constant, whose units are (atoms/mole). Therefore, multiply moles*(atoms/mole), the "mole" unit will cancel out, and you will be left with the number of atoms in the sample.

Stevin1H
Posts: 89
Joined: Fri Sep 28, 2018 12:17 am

### Re: Calculating the number of atoms

In order to find the total number of atoms within a given sample in grams, it would require conversions from grams to moles to atoms. Given the mass of the sample in grams, divide the mass of the sample (g) by its molar mass (g/mol). By doing so, this gives you the number of moles in the given sample. Now, given the moles of the given sample, remember that 1 mol=6.022x10^-23 atoms. So to convert moles to atoms, you would multiply the number of moles of the sample to 6.022x10^23 atoms to find the number of atoms in the sample.

Archana Biju 1G
Posts: 29
Joined: Fri Sep 28, 2018 12:18 am

### Re: Calculating the number of atoms

To go from mass to atoms, you would have to first convert the mass to moles. So, let's say you have 5 grams of O2 and if you convert that to moles it would be ~32 grams in 1 mole of oxygen. Then you would convert the moles to atoms using avargado's number - 6.022 x 10^23 atoms. So, if you do that with the oxygen example from above you get 9.40x10^22 atoms.
Hope this helped!

kimberlyrose1G
Posts: 44
Joined: Fri Sep 28, 2018 12:27 am

### Re: Calculating the number of atoms

First you multiply the number of grams by the atomic mass of the element (if a compound, then you would add together all of the individual atomic masses together) and that will give you the number of moles present in the sample. You would then multiply this value by Avogadro's Number (6.022 x 10^23) to get the product in the amount of atoms in the sample.

**Note that if there is a subscript on an element's symbol, you would multiply the atomic mass by this value when calculating in the first step