How many atoms are there in your body?
I really enjoyed the video to the right, and it reminded me about something cool we can do with moles  calculate the number of atoms in our body. The video features an exhibition of chemical elements held in Dublin. In one of the exhibits you can weigh yourself and then read a print out telling you the number of atoms of each different element in your body. 

The easiest way to estimate the number of atoms
in your body is to assume that your body is entirely made of water. Our bodies
are like a huge collection of tiny little water balloons. The balloons are
cells and the water inside them is the aqueous medium in which all of the
lifesustaining chemical reactions take place, so this assumption is not too
unreasonable.
Water has a molar mass of 18g mol^{1}
The average person (AP) has a mass of 70kg, which is 70,000g
The number of moles of water in an AP is therefore
70,000/18 = 3889 (4 sig figs)
Using Avogadro’s constant, the number of molecules of water in an AP is
3889
x 6.02x10^{23} = 2.341 x 10^{27}
Remembering that there are 3 atoms in each molecule of water, we can multiply by 3 to get the final answer.
The number of atoms in an average person is: 7.023 x 10^{27}
Find a more precise figure, including the
number of atoms of each different element, as well as the actual mass of gold in your body here.

Avogadro's Number (Mole)  Numberphile
The Periodic Videos team on Avogadro's number, how to measure it, how to visualise it, and its rodent namesake. 

Empirical and Molecular Formulae
Clear and effective explanation of empirical and molecular formulae from Machemguy, who has produced a huge range of videos to help Alevel chemistry students master their subject. 
Why Moles?
MaChemGuy explains how chemists devised the mole as a way to keep track of the numbers of atoms participating in reactions. 


Molar Calculations Involving Masses
Another video from MaChemGuy on how to make molar calculations using masses of substance. 