IB Chemistry SL 3.2.4 Organic Physical-property Trends

Practise comparing melting point, boiling point, volatility and solubility across homologous series and isomers. Identify the intermolecular forces present, then account…

Exam points

rank boiling points by intermolecular-force type when molecular masses are similar
explain a homologous rise through stronger London forces as electron count increases
predict branching effects from reduced surface contact between similarly sized molecules

[Maximum number: 2]

$\quad \mathrm{C}_{5} \mathrm{H}_{12}$ exists as three isomers. Identify the structure of the isomer with the lowest boiling point and explain your choice.

$\quad \mathrm{C}\left(\mathrm{CH}_{3}\right)_{4}$ ;

Marking guidance:

Accept correct name 2,2-dimethylpropane.
Do not penalize missing H atoms.
weakest London/dispersion/van der Waals'/vdW/instantaneous induced dipoleinduced dipole forces because of smallest surface area/contact
OR
weakest London/dispersion/van der Waals'/vdW/ instantaneous induced dipoleinduced dipole forces because of least distortion of the electron cloud OR
weakest London/dispersion/van der Waals'/vdW/ instantaneous induced dipoleinduced dipole forces because polarizability of electrons (in electron cloud) is less;

Accept other words to that effect but student must mention a correct IMF and a correct reason.

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3.2.4—Physical property trends question 1