**EA:**

The data adds up to 100% so there are no "hidden elements" but we don't
know the molecular weight. That doesn't matter because the data can
still
provide the empirical formula (*simplest ratio*) by considering
using
a 100g and remembering NEVER TO ROUND DATA during EA calculations (it
will
invariably mean you get the wrong answer).

%C = 83.24 divide by atomic weight
: 83.24/12.011 = 6.9303
moles

%H = 16.76 divide by atomic weight : 16.76/1.008 = 16.627
moles

So we have 6.9303 moles of C for every
16.627 moles of H, by dividing
by the smallest, that tells us for each C there are 2.4 H atoms.... or
C_{1}H_{2.4} but that is not an empirical
formula,
the simplest integer ratio is **C _{5}H_{12}**. The
easiest
way to get this is to multiply by 10 first to get rid of the decimal
then
recognise that you can divide by 2.

So the empirical formula = C_{5}H_{12}.
Since there
are only 3 isomers, this means this is also the molecular formula.

Why the boiling point order ?

Physical properties are determined by intermolecular forces (*i.e.
*the
forces between molecules) and are NOT connected to the thermodynamic
stability
(which is primarily governed by the intramolecular forces such as the
covalent
bonds).

There are 3 types of intermolecular forces : London dispersion forces,
dipole-dipole forces and hydrogen bonding.

In the alkanes for this question we are only talking about the London
dispersion forces since we lack polar bonds (so no dipole-dipole
interactions)
and no H atoms on electronegative N or O atoms (so no H-bonding).
Non-branched
structures are essentially linear in shape. A more branched structure
is
more spherical in shape and therefore has *less* surface contacts
with neighbouring molecules. This means there are *less*
intermolecular
forces and so *less* energy (hence* lower* temperature) is
required
to separate the molecules during the boiling process.