1. 7.13 – NOTES Solubility of Molecules

2. C. Solubility of molecules
“Like dissolves like”
Solubility – ability of a substance to dissolve in another substance; polar attracts polar and/or ionic;
nonpolar solvents – benzene, hexane, carbon tetrachloride
polar solvents – water and alcohols

4. D. Properties of covalent compounds
1. Compare ionic and covalent compounds:
Ionic Covalent
- mostly solid - S, L, G (solid state forms a lattice similar to ionics but with less strength); G = O2, H2S, CO2
- high MP/BP - low MP, BP
- water soluble - solubility varies greatly in water
- conducts electricity - poor conductors
- hard relatively soft (paraffin)
-vaporize readily at room temperature

5. 2. Attractive forces between molecular compounds
Ionic compounds exist in large crystal structures called lattices. The attractive forces holding the crystal together are ionic bonds.
Covalent compounds are held together internally by covalent bonds.
But what forces hold the molecules near each other? For example, why does water exist as a liquid?
What holds covalent molecules close to each other are intermolecular forces, also called van der Waals forces.

6. The intermolecular forces can be divided into categories: London dispersion forces and dipole-dipole forces.

7. London dispersion forces:
Exists between all molecules; play a significant role in non polar molecules;
Form as a result of a temporary dipole so it is a weak force; there is a noticeable effect as the # of electrons increases;
F2, Cl2, Br2, I2 as diatomic molecules
the larger halogen molecules have more e-s so there can be a greater difference between the (+) and (-) regions of their temporary dipoles, therefore stronger dispersion forces; F and Cl are gases, Br is a liquid, and I is a solid at room temperature;

9. Dipole –Dipole forces: stronger than London dispersion forces; exists b/t polar substances; the more polar the molecule (the greater the difference in Electronegativity), the stronger the force;

12. Hydrogen bonds: a special type of dipole force: hydrogen bonds to either F, O, N;
especially strong dipole-dipole force;
O-H bonds are more polar than N-H bonds, as a result, H-bonds b/t water molecules are stronger than those b/t ammonia molecules; CH3OH vs. CH3F,