What is meant by the term 'mole' (and its unit, 'mol') in chemistry? (Hint: not a small burrowing mammal)

A #"mol"# is essentially a large quantity, equal to about #6.022xx10^23# (Avogadro's number).

The number is chosen, though, so that a large quantity of quantum-sized objects (i.e. atoms, molecules, etc) can be described in more manageable, less awkward values.

For instance, instead of saying we have #6.022xx10^23# atoms, which is a bit awkward, it is more convenient to say:

#6.022xx10^23 cancel"atoms" xx ("1 mol")/(6.022xx10^23 cancel"atoms")#

#=# #color(blue)("1 mol of atoms")#

It's just a new unit to express a large quantity of things.

#"1 mol"# of pictures is the same quantity as #"1 mol"# of thumbdrives is the same quantity as #"1 mol"# of paper towels. They aren't the same mass, but there are the same number of them.

We have defined our units so that, for example, the atomic mass of #""_6^12"C"#, the carbon-12 isotope, is #"12 amu"# (atomic mass units). That is the mass of one atom of carbon-12. But if we express the mass as #"12 g"# instead, that is the mass of #"1 mol"# of carbon-12 atoms.

The #"mol"# concept is handy because #"1.0079 g"# of #"H"# is #"1 mol"# and #"15.999 g"# of #"O"# is #"1 mol"#, etc.

Suppose we have #"25 g"# of #"N"_2# and want to know how many #"mol"#s that is.

The molar mass of #"N"# atom is #"14.007 g/mol"#, so the molar mass of #"N"_2# is #"28.014 g/mol"#.

#25 cancel("g N"_2) xx ("1 mol N"_2)/(28.014 cancel("g N"_2))#

#~~ "0.892 mol",#

which is a smaller number and easier to work with.