SolutionsLike dissolves Like

• Describe the terms electronegativity and polarity

• Explain the solution process of simple ionic and covalent compounds

Include: dissociation, hydration, heat of solution 

Additional KEY TermsPolar Non-polarSolvation

Electronegativity • The attraction an atom has for the shared pair of

electrons in a bond

The most electronegative element is fluorine = 4.0 The least electronegative element is cesium = 0.7

• In a compound, the atom with the higher electronegativity pulls the SHARED electrons closer

POLAR COVALENT• Unequal sharing of bonding electrons• Creates positive and negative dipoles at opposite

parts of compound• Bigger EN difference - more polar the bond

+ + HClδ+δ-

NON-POLAR COVALENT• Equal sharing of bonding electrons• NO dipoles – no permanent charges• Small EN difference

Diatomics and compounds of C and H are non-polar

Cl Cl

chlorine gas

C

C

C

H

H

H

H

H

H

H

H

C

H H

H

H

methane

propane

IONIC• Give/take of electrons between M and NM• Creates charged IONS• REALLY big EN difference

+ -

Some molecules can contain polar bonds, but because of the shape are considered to be non-polar molecules.

Dissolving vs.Dissociating

Sugar vs. Salt

**The general dissolving rule is like dissolves like.**

Solvation: the process of dissolving…

• Particles of solute will dissolve IF it is more attracted to the solvent particles than to itself

There are 3 steps to the dissolving process:

1. Solute particles must break apart. • Requires energy (lattice energy) to break IMFs

2. Solvent particles spread apart to make room.

• Requires energy to reduce solvent IMFs

3. Solute and solvent particles come together. • Releases energy

Heat of solution - the sum of the energy changes for (usually endothermic overall)

Water a polar molecule

• If a solute is attracted to water it will dissolve

• When water is the solvent – hydration

**The general dissolving rule is like dissolves like.**

H

Cl

HOH

H

O

H

Cl

H

H

O

H

H

OH

δ-

δ+

δ-δ+

δ+

DISSOLVE

√

δ-

δ+

polar solvent ionic solute

HOH

H

O

H

H

O

H

H

OH

+

-δ-

δ+

δ+

NaCl

NaCl

DISSOLVE

√

polar solvent polar solute

H

O

H

H H

H

H

C C

H

O

H

H H

H

H

C C

H

O

H

H

O

Hδ-

δ+δ-

δ+

δ-δ+

DISSOLVE

√

• Charged solutes (polar covalent or ionic) are attracted to charged solvents to various degrees

*The more soluble a solute is, the more attracted to the solvent it must be*

• Uncharged particles (non-polar) are only soluble in uncharged solvents

**The general dissolving rule is like dissolves like**

polar solvent non-polar solute

H

O

H

H

O

Hδ-

δ+δ-

δ+

C

H H

H

H

C

H H

H

H

DISSOLVE

No dipoles Nothing to attract too

H

C

C

H

C

H H

H

H

non-polar solvent non-polar solute

C

H H

H

H

H

C

C

H

DISSOLVE

√

No dipoles No attraction or repulsion - Free to mix

SOAP• Has a polar end and a non-polar tail

• Non-polar tail attracts oil• Polar head attracts water

This allows the ball of grease to "dissolve" in the water

H

O

H

H

O

H

HOH

HO

H

CAN YOU / HAVE YOU?

• Describe the terms electronegativity and polarity

• Explain the solution process of simple ionic and covalent compounds

Include: dissociation, hydration, heat of solution 

Additional KEY TermsPolar Non-polarSolvation