Temporary and Permanent dipoles

What are intermolecular bonds?

The forces between molecules, causing them to be attracted to each other and not just move apart to become a gas.

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In the noble gases, energy is only required to separate the atoms, because there are no...?

Covalent bonds

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The larger the atoms, the ___ the bonds between them?

stronger

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The longer the alkane chain, the ___ the boiling point?

higher

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What is a dipole?

A molecule or part of a molecule that has a positive end a negative end.

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What is the partial charge on the H atom in HCl?

positive

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When a molecule has a dipole, it is ___?

polarised

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When do permanent dipoles occur?

When a molecule has two atoms bonded together with substantially different electronegativities, meaning one atom attracts the shared electrons much more than the other.

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Which atom is more electronegative in HCl and what effect does this have?

Chlorine - attracts the shared electrons more.

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Molecules with a permanent dipole are said to be ___ ___?

polar molecules

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How may an instantaneous dipole arise in a Chlorine molecule?

The electrons in the negatively charged cloud are in constant motion and at any one instant they may not be evenly distributed over the two atoms.

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An instantaneous dipole can affect nearby molecules and cause an ___ ___?

Induced dipole

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How is a dipole induced in an unpolarised molecule?

The dipole in the polarised molecule attracts or repels electrons in the charge cloud of the unpolarised molecule.

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All intermolecular bonds arise from...?

The attractive forces between dipoles.

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What is a permanent dipole-permanent dipole?

Where two or more permanent dipoles attract each other.

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What is a permanent dipole-induced dipole?

A permanent dipole induces a dipole in another molecule, then the two attract each other.

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What is an instantaneous dipole-induced dipole? Where does this commonly occur?

Instantaneous dipole induces a dipole in another molecule, then attracts it. Noble gases.

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Instantaneous dipole-induced dipole bonds are the ___ type of intermolecular bonding and they occur in ___ molecules?

weakest, all

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Why are Xenon atoms more polarisable than Helium atoms?

The Xenon atom is bigger, with more electrons, so the outer electrons are less strongly held by the positive nucleus and more easily pushed around from outside.

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Why do straight chain alkanes have higher boiling points than branched chain alkanes?

More contacts between atoms of different molecules - more opportunities for induced dipoles to form.

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The more atoms in a molecule, the ___ the bonds?

stronger

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Explain why CCl4 is non-polar?

Each Cl atom carries a small negative charge and the central carbon is positive but because the Cl atoms are distributed symmetrically around the C atom, the centre of negative charge is midway between all the Chlorines, so there is no overall dipole

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Therefore a molecular dipole depends on ___ differences and ___ of the molecule?

electronegativity, shape

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Substances with permanent molecular dipoles are liquid at room temperature, explain why?

Molecules constantly moving and tumbling around, different ends of different molecules will line up so some attract and some repel each other. But overall there is more attraction than repulsion. There will also be pd-id and id-id bonds present.

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Bonds are stronger if the ___ of the dipoles increase or if the interacting dipoles are able to...?

size, approach each other closely

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Temporary and Permanent dipoles

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