What is relative number of atoms?

The relative number of atoms is the empirical formula.

The relative number of atoms

A compound consists of two or more atoms joined together in a fixed ratio.

For example, in water, #"H"_2"O"#, the relative number of hydrogen and oxygen atoms is #"H:O =1:2"#.

In hydrogen peroxide, #"H"_2"O"_2#,the relative number of hydrogen and oxygen atoms is #"H:O =1:1"#.

We can't see the atoms, so all we can do is determine the relative numbers of each type.

For example, the molecular formula of hydrogen peroxide could be #"HO, H"_2"O"_2, "H"_3"O"_3#, etc.

The formula with the smallest relative numbers is the empirical formula.

Finding the empirical formula

The empirical formula is the simplest whole-number ratio of atoms (i.e., their relative numbers) in a compound.

The ratio of atoms is the same as the ratio of moles.

So, our job is to calculate the molar ratio of #"Xe"# to #"F"#.

Your compound contains 55.35 % #"Xe"# and 46.5 % #"F"#.

Assume that you have 100 g of sample.

Then it contains 53.5 g of #"Xe"# and 46.5 g of #"F"#.

#"Moles of Xe" = 53.5 color(red)(cancel(color(black)("g Xe"))) × "1 mol Xe"/(131.29 color(red)(cancel(color(black)( "g Xe")))) = "0.4075 mol Xe"#

#"Moles of F" = 46.5 color(red)(cancel(color(black)("g F"))) × "1 mol F"/(19.00 color(red)(cancel(color(black)("g F")))) = "2.447 mol F"#

From this point on, I like to summarize the calculations in a table.

#ulbb("Element"color(white)(m) "Mass/g"color(white)(X) "Moles"color(white)(m)"Ratio"color(white)(m)"Integers")#
#color(white)(m)"Xe" color(white)(XXXmm)53.5 color(white)(Xm)0.4075 color(white)(mll)1color(white)(mmmmml)1#
#color(white)(m)"F" color(white)(XXXXmll)46.5 color(white)(mm)2.447 color(white)(Xml)6.006 color(white)(mmml)6#

Although there are almost the same masses of #"Xe"# and #"F"#, the relative number of atoms is #"Xe:F = 1:6"#.

The empirical formula is #"XeF"_6#.