# How many atoms of neon are in 5.9 grams of neon?

Nov 8, 2015

$1.8 \cdot {10}^{23} \text{atoms}$

#### Explanation:

The idea here is that you need to use neon's molar mass, which tells you what the mass of one mole of the element is, to determine how many moles you have in that $\text{5.9-g}$ sample.

Once you know how many moles you have, you can use Avogadro's number to find the number of atoms.

So, neon has a molar mass of $\text{20.18 g/mol}$, which means that every mole of neon has a mass of $\text{20.18 g}$.

Your sample of neon will thus contain

5.9color(red)(cancel(color(black)("g"))) * "1 mole Ne"/(20.18color(red)(cancel(color(black)("g")))) = "0.2924 moles Ne"

Now, you know that one mole of any element contains exactly $6.022 \cdot {10}^{23}$ atoms of that element - this is Avogadro's number.

Well, if one mole contains that many atoms, it follows that you sample will contain

0.2924color(red)(cancel(color(black)("moles Ne"))) * (6.022 * 10^(23)"atoms of Ne")/(1color(red)(cancel(color(black)("mole Ne")))) = color(green)(1.8 * 10^(23)"atoms of Ne")

The answer is rounded to two sig figs, the number of sig figs you have for the mass of the sample.