POLAR AND NON POLAR MOLECULES AND INTERMOLECULAR FORCES

polar

❑ Asymmetric
❑ With unshared electrons (lone pairs)
❑ Terminal atoms are different
❑ Same electronegativity values
❑ Partial positive and partial negative charges

nonpolar

❑ Symmetric
❑ Equal sharing of electrons
❑ Terminal atoms are the same
❑ Different electronegativity values
❑ Same charges

examples of polar

❑ Water – H2O
❑ Ammonia – NH3
❑ Sulfur dioxide – SO2
❑ Hydrogen sulfide – H2S
❑ Carbon monoxide – CO
❑ Ozone – O3
❑ Hydrofluoric acid – HF (and other molecules with a single H)
❑ Ethanol – C2H6O (and other alcohols with an OH at one end)
❑ Sucrose – C12H22O11 (and other sugars with OH groups)

examples of nonpolar

❑ Any of the noble gases: He, Ne, Ar, Kr, Xe (Although, technically these are atoms and not molecules.)
❑ Any of the homonuclear diatomic elements: H2 , N2 , O2 , Cl2 (These are truly nonpolar molecules.)
❑ Carbon dioxide – CO2 ❑ Boron trifluoride – BF3
❑ Benzene – C6H6
❑ Carbon tetrachloride – CCl4
❑ Methane – CH4
❑ Ethylene – C2H4
❑ Hydrocarbon liquids, such as gasoline and toluene
❑ Most organic molecules, with exceptions (like alcohols and sugars)

dipole

a pair of equal and oppositely charged or magnetized poles separated by a distance

polar molecules

type of molecules wherein terminal atoms are different, not symmetrically arranged, one end is partial positive, and the other is partial negative

nonpolar molecules

type of molecules wherein terminal atoms are the same, symmetrically arranged and have the same charges

electronegativity

a measure of an atom’s ability to attract electrons towards itself. Increases as you move to the right of the periodic table and decreases as you move down.

intermolecular forces

❑Attractive forces that act between molecules or particles in the solid and liquid and influence their physical properties and behavior.

❑Weaker than bonding forces

❑Can be broken if there is a high temperature (increased kinetic energy)

❑Solid melts, liquid evaporates
❑The stronger the intermolecular forces, the larger the amount of energy needed to break them, hence, higher melting point and boiling point

LONDON DISPERSION

❑Dispersion forces

❑Exist in all atoms and molecules

❑Only force that acts on non-polar molecules

DIPOLE – DIPOLE

❑Exist between polar molecules

❑Partial positive end of one molecule is attracted to the partial negative end of another molecule

HYDROGEN BOND

❑Special type of dipole-dipole

❑Exist only in molecules that contain a hydrogen atom bonded to a small, highly electronegative atom such as N, O, or F. (not the same as a covalent bond)

ION – DIPOLE

❑Ion (charged particle) and a polar molecule

❑Quite strong as compared to van der Waals forces

❑Significant in solutions (ionic compounds dissolved in polar solvents)

❑Salt in water