Ar, mr

How many molecules of water are there in a 500 ml bottle of mineral water?

This is the number of water molecules in 500 ml of water give or take a few.

This is the number of water molecules in 500 ml of water give or take a few.

This is the number of hydrogen and oxygen atoms in 500 ml of water. Atoms and molecules are really very small and have tiny masses.

Instead of dealing with the actual masses of atoms, chemists use the massesof atoms relative to a standard atom.

The standard atom chosen is carbon-12, C.126

This is the definition of relative atomic mass.

Let's look at some Ar values.

These Ar values are precise to five significant figures.

Remember that carbon is the standard atom with a defined Ar value.

The Ar values are not whole numbers because they are averages that take intoaccount isotopes of each element.

Ar values precise to one decimal place are usually used when doing calculations.

We don’t need to know the true mass of hydrogen and oxygen atoms to see thatoxygen atoms are sixteen times heavier than hydrogen atoms.

Instead of dealing with the actual masses of the particles in compounds, chemists use their formula masses relative to a standard atom.

The standard atom chosen is carbon-12, C.126

Relative formula mass is also called relative molecular mass when dealing withmolecules.

The Mr of a compound is calculated by adding together the Ar values of all theatoms in its formula.

Work out how many atoms of each element there are in the compound.

Work out how many atoms of each element there are in the compound.

Work out how many atoms of each element there are in the compound.

Look up the Ar values for each element.

Multiply the number of each atom by its Ar value.

Add everything together to get the Mr.

Add everything together to get the Mr.

The Mr of a compound is calculated by adding together the Ar values of all theatoms in its formula.

Work out how many atoms of each element there are in the compound.

Look up the Ar values for each element.

Multiply the number of each atom by its Ar value.

Add everything together to get the Mr.

Add everything together to get the Mr.