Chemistry Test Part 2 Review

Na and Cl ions are layered (3-D) to form a CRYSTAL LATTICE. What characteristic properties do salts (Ionic Compounds) have?

Properties:

•Form crystals (hard/brittle)

•High melting point

•Soluble in water (why?)

•Conduct electricity in solution (why?)

Remember: Water is a Polar Molecule

_

It’s attracted to both positive AND negative charges

+

What makes water polar??

•Unequal sharing of the electrons creates slight positive/negative dipoles

•Other molecules, such as Ethane, are nonpolar, having neither a positive nor a negative side.

•Can Ethane dissolve in water?

•NO! Remember “like dissolves like”!

The polar water molecules are attracted to the + and – ions in the crystal lattice

−

−

−

What does “Solvation” mean?

Solvation is where the charged ends (dipoles, + -) of water molecules interact with the ions in a crystal lattice (like NaCl). The result is a solution of dissolved sodium chloride.

−

−

−

When dissolved, the Na+ and Cl- ions are surrounded by water molecules and float freely in the solution.

• It’s the movement of ions in a liquid that allows a solution to conduct an electric current (see example below)

• Pure mineral oil does not conduct electricity.

• Why? Because like pure water, mineral oil does not contain + or – ions.

+ Probe – Probe

_

_

_+

++

+

_+

Ionic solid ex. NaCl

Oil is nonpolar

1.5 volts

=

Remember:Free moving Ions = Conductivity

No Ions, No conductivity in a solution!

Why doesn’t wax dissolve in water?

Dipole vs No Dipole (Non-Polar)

WAX is Non-polar Covalent

+-

- +

+-

-

+

+- +

+-

-+ - +

-+

-+

+

-

Water and alcohol, both polar molecules, mix together.

-

+

-

Baby Oil is non-polar so it does not mix with either water or alcohol. Being less dense, it floats on top.

+ -

Remember this??

WAVE TOY

+ -

+-

-+

“Like Dissolves Like”= Polar dissolves polar

+ Water-based red dye

Baby Oil

What characteristic properties do Non-polar substances have?

Properties:

•Soft

•Low melting point

• NOT Soluble in water (why?)

•Do NOT Conduct electricity in solution (why?)

What characteristic properties do Polar substances have?

Properties:

•Crystals (solid)

•Medium melting point

• Soluble in water (why?)

•Do NOT Conduct electricity in solution (why?)

What else is important to know about water?

Why does water expand when it freezes?

Because of the hydrogen bonds between water molecules. When water freezes, H bonds move and push the water into a more regular or “lattice” shape, causing it to expand (increased volume = less density). This is why ice floats!

Why does water have a high boiling point?

Again, because of the hydrogen bonds between water molecules. Water must be heated to a relatively high point before the motion of the molecules is great enough to break the hydrogen bonds. At this point the liquid water turns to a gas (steam)

Metals

Why are metals such good conductors of electricity?

Metals hold on to their valence electrons very loosely. A small amount of force (voltage) starts a “leap frog” chain reaction, with e- moving from one atom to the next.

Compare/Contrast Metals and Non-metals

Compare and Contrast Metals and Non-metals.

Metals (Left side of Periodic Table)

• Few valence e-, low Ionization Energies (less energy required to pull e- away)

• Share e- with other metals; lose e- to non-metals (& form ionic compounds like salt)

Non-metals (Right side of Periodic Table)

• More valence e-, high Ionization Energies

• Share e- with other non-metals; steal e- from metals (= ionic bonds).

Electronegativity

Electronegativity: What is it? Electronegativity: A measure of an atom’s “hunger” for

electrons, or how much energy it has to attract electrons

• Florine (electronegativity = 4.0) has the greatest hunger for an electron. Neon, with 8 valence e-, has no electronegativity (already has a full outer shell).

The Cookie Monster would have a lot of Electronegativity!

Me like electrons!!

Highest

Generally, electronegativity increases as you move left to right and from bottom to top (except for He, Ne, & Ar in last column)

The difference in electronegativity between two atoms will determine the type of bonding that occurs:

0.5 – 2.0< 0.5 >2.0

Electronegativity Difference = Tug of War

Equal Strength = Non-Polar Covalent

Sharing e-

One Stronger = Polar Covalent

Not Equal Strength = Polar Covalent Sharing e- but one is being an e- HOG

Stealing e- = Ionic

Why share e- if you’re strong enough to steal?