Lesson 4.2 Explaining Solutions SCH 3U

Polar Molecules For example, water.

Non- Polar Molecules

INTERMOLECULAR FORCES Based on polarity of molecules, intermolecular forces are the attractive forces between two molecules.

Hydrogen Bonding Molecules that have a covalent bond between an H and O, F, or N (the three most electronegative atoms) H atom interacts with LONE PAIR of electrons on a nearby atom. VERY STRONG attraction

N H Hydrogen Bonds  -  +  +  + Will H-Bonding occur between this molecule and water?  - N H 3.0  + 2.1  + 2.1 2.1  +

The Effects of Hydrogen Bonds Multiple hydrogen bonds between water and ammonia result in a very high solubility for ammonia

Determining the Polarity of a Molecule

Draw the Lewis Structure Draw the shape diagram. Assign the electronegativities of the atoms. Assign  + and  - to each of the bonds Draw in the bond dipoles (point towards more negative). Draw the dipole moment (overall dipole of the molecule)

Vitamins – Water soluble and fat soluble Vitamin C Vitamin B-6

VITAMINS Vitamins A, D, E and K are FAT SOLUBLE Vitamin D

Molecular substances Molecular substances are made of atoms that are COVALENTLY BONDED together. How are they soluble? Molecular solute is surrounded by water molecules that are attracted to the polar OH’s SUCROSE

Miscible: E.g. water and ethanol Immiscible: E.g. water and gasoline

Other examples – Molecular substances OIL IN GASOLINE – miscible – both are non- polar (London dispersion forces) OIL IN CYCLOHEXANE – miscible – both are non-polar (London dispersion forces) GLUCOSE IN WATER – miscible – both are polar (H-bonding) OIL IN WATER – immiscible– oil is non-polar, water is polar. RULE:

Common Solvents Cyclohexane Polar N.P. Toluene Polar N.P.

IONIC COMPOUNDS Cl- Cl- Cl- Na+ Na+ Cl- Na+ Cl- Cl- Cl- Na+ Cl- Na+

Why Are Ionic Compounds So Soluble in Water? Ionic compounds dissociates in water to form electrically charged IONS. Positive ions (cations): surrounded by (-ve) ends of water molecules (Oxygen) Negative ions (anions): surrounded by the (+ve) ends of water molecules (Hydrogen). Polar water sticks to ions on the surface of an ionic compound. Attraction of surface ions to the rest of the crystal is weakened. Water molecules surround the surface ions and carry them away from the crystal. Result: ionic compounds dissociate in water See text page 278.

What did one dipole say to the other?

The bear from Alaska, because it’s more POLAR!!! A bear from Alaska and a bear from California dive into a freshwater pool. Which one dissolves faster? The bear from Alaska, because it’s more POLAR!!!