CHEM 1AA3 Study Guide - London Dispersion Force, Van Der Waals Force, Neopentane
26 Nov 2013
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London dispersion forces eg. iodine (non-polar, no permanent dipoles) Also called induced dipole- induced dipole forces. Spontaneous, temporary fluctuations in electron density that propagates throughout sample; creates a dipole that causes an attraction between two neighbouring molecules. Force strength depend son polarizability (tendency or charge separation to occur) Force strength increase with: atomic number and size of the molecule (due to polarizability) 387 k gas at room temp solid at room temp: linear vs branched structures (b/c of increased intermolecular contact area. Pentane, zig-zag straight chain of c5h12, boiling point = 36. 1c. Long chain form allows them to stack close and efficiently together, provides a lot of surface area for them to connect. Spherical nature of neopentane doesn"t give a lot of surface area for it to connec tith other neopentane molecules. Occur in polar molecules (molecules with permanent dipoles: polar molecules have bond dipoles and asymmetric shape (eg. acetone is polar, while carbon dioxide is not polar)
