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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?)
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”!
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
=
+-
- +
+-
-
+
+- +
+-
-+ - +
-+
-+
+
-
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?)
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)
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 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: 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!!
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
One Stronger = Polar Covalent
Not Equal Strength = Polar Covalent Sharing e- but one is being an e- HOG