Relative formula mass.

https://www.youtube.com/watch?v=q49NwIrjaFw&list=PL9IouNCPbCxUhxxFUbR4SNfwmaRB8mYX3&index=5&ab_channel=Freesciencelessons

Whats the relative formula mass (Mr)

The relative formula mass of a compound is the sum of the relative atomic masses of the atoms in the numbers shown in the formula.

Key points about relative formula mass.

It has no units.

Relative formula mass never involves big numbers

Whats the Mr of methane (CH4)

We have one atom of carbon and 4 atoms of hydrogen

Ar of C is 12

Ar of H is 1

so 12 + (1×4) is 16. Mr is 16.

What happens when you put a large 2 infront of CH4

This means that we now have 2 molecules of methane.

Remember that we do not use big numbers to calculate Mr

Therefore the Mr is still 16.