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Chapter 14 Liquids and Solids. How do the particles of a gas behave? Motion? Attraction? Arrangement? As a result, gases have low densities, are highly compressible and conform completely to the shape of a container. Let’s compare that to solids
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How do the particles of a gas behave? • Motion? • Attraction? • Arrangement? As a result, gases have low densities, are highly compressible and conform completely to the shape of a container. • Let’s compare that to solids • High densities, basically incompressible, rigid, maintain their own shapes • The properties of liquids are in-between • Liquids are more closely related to solids than they are to gases.
What process is illustrated? Melting
What process is illustrated? Boiling / Evaporation
14.1 intermolecular forces • Most substances consisting of small molecules are gasses at room temperature and pressure (a notable exception is water) • Intermolecular forces are sources of attraction between molecules. • Dipole-dipole attraction • Hydrogen Bonding • London Dispersion Forces
dipole-dipole attraction • polar molecules get together b/c of mutual attraction • the ∂+ of one is attracted to the ∂- of the other • they find the best orientation, too, for maximum “stickiness” • only about 1% as strong as covalent
hydrogen bonding • Particularly strong intermolecular force • Occurs when hydrogen is bound to a highly electronegative atom (e.g. F, N) • The extremely unequal sharing of the Hydrogen’s one electron creates a very strong dipole
water molecules have a strong attraction for each other • their attraction is called an H-bond • represented by------ lines • [not true bonds, just really strong attractions]
This also happens with molecules which have N-H and F-H bonds • water, ethanol, ammonia all have H-bonding • it’s the reason they all are liquids when they aren’t supposed to be (i.e. similar sized molecules without H-bonding are all gases)
it has a significant affect on the properties of H-bonded molecules by making them cling to each other more • boiling points are higher because it is so hard to separate them
londondispersionforces • what about nonpolar substances? how can they be attracted to each other and form a liquid? • they are attracted by london dispersion forces • some atoms, although nonpolar overall can experience temporary, instantaneous dipoles
nonpolar moleculescanform these attractions • they have to be slow and close for any significant effect, but… • large molecules (e.g. I2) form them more easily because of all the electrons involved