Warmup 1)What are some of the factors that affect solubility of a compound? 2) A solution of potassium carbonate and a solution of copper(I) nitrate are.

Warmup1) What are some of the factors that affect

solubility of a compound?

2) A solution of potassium carbonate and a solution of copper(I) nitrate are combined. Write the net ionic equation showing formation of the precipitate.

*review your solubility rules. Remember that according to these rules, the salts are soluble/insoluble at a certain concentration 0.1M.

Solubility, Polarity, and Forces

1. Increase surface area of the solute: agitate the solution or break up solute

1. How can we increase the rate of dissolution (how fast the solute dissolves) and solubility?

2. Heat the solution (s and l solutes): molecules move faster and collide more frequently

3. Cool the solution (gas solutes): gas molecules won’t evaporate (lowering solubility) if they have less kinetic energy.

4. Increase pressure (gas solutes): solute can’t

evaporate and remains dissolved in the solution

How can we increase the rate of dissolution (how fast the solute dissolves) and solubility?

Polar(P) Molecules-Shared e- are unequally distributed among atoms -All ionic compounds are P

Nonpolar (NP) MoleculesPretty even e- distributionMost very large molecules are NP

Why does oil not dissolve in water or vinegar? Oil (NP) likes water(P)! But water molecules prefer each other than oil.

It is NOT because the

molecules repel.

“like dissolves like”

Polar solvents are soluble in polar solutesNonpolar solvents are soluble in nonpolar solutesThere are different degrees of solubility….many things are

slightly soluble.

Water and acetate have weak dipole-dipole interactions.

They are soluble; one dissolves in the other!

Why are these molecules a soluble combination?

(draw please)

H -

Molecules aren’t just polar or nonpolar. Rank these molecules from most(1) to least(4) polar.

HO-H

H HH-C-O-C-H H H

H H O HH-C-C-C-H H H H

H H H H H H H-C-C-C-C-C-C-H H H H H H H

Which compound to the right would be the best solvent for NaCl? Explain.

methanol

H-O-Cl

hexaneisopropyl alcohol

dihydrogen monoxide

1

2

34

HH-C-O-H H

(please draw in lone pairs yourself)

Intermolecular Forces (IMF)(Van der Waal forces)

• much weaker than ionic OR covalent bonds• due to attractive forces between opposite charges (+ and -)• make solid and liquid molecular compounds possible• explain variation in melting and boiling points (etc)

Two Main Types:1. weaker: London Dispersion Forces

(“induced dipoles”)2. stronger: Dipole Interactions (hydrogen

bonding is one type)

Physical Properties of Nonpolar HalogensHalogen Molecular Mass

(g/mol)Melting Point

(oC)Physical State at

Room Temperature

Fluorine, F2 38.0 -219.6 Gas

Chlorine, Cl2 70.9 -101.5 Gas

Bromine, Br2 179.8 -7.3 Liquid

Iodine, I2 253.8 113.7 Solid

Describe and account for these trends.As molar mass increases, melting point increases. The size of the electron cloud MUST play a role in the amount of

energy required for a phase change (evaporation too).

London Dispersion Forces

• electrons on one molecule distorting the electron cloud on another all molecules have them

• bigger molecule (mass), more electrons, larger induced dipole, stronger LDF, more energy needed to break free!

+

----

- -- --

-

+

----

- -- --

-

+

+

++

---

--

----

--

-

-

-

-

+

+

++

---

--

----

--

-

-

-

-

To melt a solid compound, it is necessary to provide enough energy for each molecule to overcome the attractive intermolecular forces holding it in place.

Which of the following would have the lowest boiling point? Explain.

CH3CH3 C3H8 CH4

ethane propane methane

Lowest mass, lowest LDF!

Dipole interactionsCaused by permanent dipole of polar molecules

As e- are pulled away from H by F, what is left is an unshielded proton that will strongly attract neighboring e-

(+) and (-) ends of compounds attract one another (but are not completely hooked like ionic compounds)

H Fd+ d-

H Fd+ d-

Hydrogen Bonding

HH

Od+

d-

d+

H HOd

+

d-

d+

- One type of dipole-dipole interaction- The strongest of the IM forces2. According to the diagram, what causes formation of H-bonds?

weak H bonds hold DNA

bases together

H on one molecule partially shares the lone pair on F, O, and N

Revisiting some of these same compounds, which would have high boiling points? Which would have low boiling points?

HO-H

H HH-C-O-C-H H H

H H O HH-C-C-C-H H H H

H H H H H H H-C-C-C-C-C-C-H H H H H H H

High: polar stuff like methanol and isopropyl alcohol

methanol

hexaneisopropyl alcohol

dihydrogen monoxide

HH-C-O-H H

Low: nonpolar stuff like dimethyl ether, hexane.