Molecular Polarity and Intermolecular Forces

electronegativity

The ability of an atom to attract shared electrons within a bond.

nonpolar covalent bonding

Electrons are shared equally (ΔEN = ≤0.4).

polar covalent bonding

Electrons are shared unequally (0.4 < ΔEN < 1.7).

ionic bonding

Electrons are being transferred (ΔEN ≥ 1.7).

bond polarity

The difference of electronegativity between electrons being bonded.

molecular polarity

Determined by the 3-D shape of the molecule; to be polar, a molecule must have a definite negative and positive end.

intramolecular forces

Forces __**within**__ a compound or molecule between the atoms in it.

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* Ionic bonds, metallic bonds, nonpolar covalent bonds, polar covalent bonds

intermolecular forces

Forces __**between molecules**__; can only exist between __**identical**__ molecules.

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Responsible for the observed __**physical properties**__ of molecular compounds, such as boiling point, melting point, and electrical conductivity.

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Determined by __**molecular shape**__ and __**molecular polarity**__.

London Dispersion Forces

* Attraction between **temporary dipoles**
* Exists in __**all molecules**__ both polar and non-polar
* Caused by the electrons of one molecule being **attracted** to the nucleus of another molecule; forming __**temporary (instantaneous) induced dipoles**__.
* The **more** electrons a molecule has (from larger atoms / bigger atoms), the __**stronger**__ its London forces because there is a __more prominent temporary dipole__. This is called **polarizability** (**more distortable**).

polarizability

The more electrons a molecule has (from larger atoms / bigger atoms), the __**stronger**__ its London forces because there is a __more prominent temporary dipole__ (more distortable)

Dipole-Dipole Forces

* Attraction between **permanent dipoles**
* Occurs in __**all**__ **polar** molecules
* Caused by the attraction of the **partial positive** end  (δ+) of __one__ molecule to the **partial negative** end (δ-) of __another__ molecule, and vice-versa

Hydrogen Bonding

* Attraction between **permanent dipoles: F-H, O-H, N-H** (FON)
* __**Special**__ type of __dipole-dipole__ force that is very strong
* Caused by the **attraction** of hydrogen atoms __**bonded**__ to __F, O, N__ (high EN) in __**one**__ molecule to the **lone pair** of electrons on the __F, O, N__ atom of __another__ molecule