Physical Science. Chapter 20: Chemical Bonds. Compounds. A compound is a combination of atoms from 2 or more different elements, in a definite ratio The properties of a compound may be completely different from those of the elements which make it up. Example: water (H 2 O).
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Chapter 20: Chemical Bonds
Hydrogen - 2 atoms
Sulfur - 1 atom (understood subscript)
Oxygen - 4 atoms
(Outer shell electrons refers to the electrons that are farthest out from the nucleus in the electron cloud)
Ex. He-2 ose's, Ne-8, Ar-8, Kr-8
For example: Mg G2 2 o.s.e.’s
N G15 5 o.s.e.’s
Cl G17 7 o.s.e.’s
Kr G18 8 o.s.e.’s
So.....magnesium has 2 ose's, and would therefore have 2 dots surrounding it.
H He Al C
N O Cl Ne
1. Ionic - bonds created by the attraction of opposite charges (+, -) like a magnet
2. Covalent - bonds created by the sharing of electrons
If chlorine were to gain 1 electron, then it would have 8, and be stable.
So it "steals" sodium's electron to become
Sodium, however, now drops down an energy level and ends up with 8 outer shell electrons also. So everybody's happy.
By sharing, H will have 2 (stable)
and Cl will have 8 (stable)
O2 (oxygen gas)
(numbers which show how many electrons are gained, lost, or shared when 1 atom combines with another).
Oxidation numbers show the number of electrons gained, lost, or shared when an atom combines.
Oxidation numbers are the same for elements in the same groups.*
Ex.: G17 elements gain 1 electron when bonding, and thus have an ox. # of -1.
+1 +2 +3 +4 -3 -2 -1 0
The criss-cross method +3 +4 -3 -2 -1 0
Oxidation numbers can be written as a superscript for each of the elements in a binary compound. Those numbers are then criss-crossed down and used as subscripts for the other element.
Cross the +2 and the -3 down to the subscript of the other element, drop the signs, and you end up with Mg3N2.
Calcium has an oxidation # of +2, chlorine is -1, what is the formula for a compound of calcium and chlorine?
Al + N = aluminum nitride
Ca + P = calcium phosphide
Acids are corrosive, although their relative strength will vary greatly.
This is usually not the case with corrosive materials. Why?
Write formulas, give names, and calculate molecular masses for each of the following compounds:
Al + Cl
Ca + O
Na + N
H + S
K + F
C. Corrosive, but not toxic
D. Toxic, but not corrosive
(assume materials are at everyday common strengths)
+1 +2 +3 +4 -3 -2 -1 0 listed in order from most stable to least stable. What do you think is the main determining factor of stability in these molecules?
-P3 element with 6 outer shell electrons
-the lightest inert element
-the lightest binary compound (17 a.m.u.)
-the lightest diatomic molecule
Give 1 example for each of the following: composed of hydrogen and sulfur:
Ch. 21: Chemical Reactions
A short-hand way to show a chemical reaction by using formulas and symbols is called a chemical equation.
Example: H2 + O2g H20
In a chemical equation, the reactant(s) are always on the left hand side, and the product(s) are always on the right.
H2 + O2g H20
We'll get to that later.
Those symbols are on pg. 635 in your book.
Therefore, the mass of the reactants before the reaction occurs must be exactly equal to the mass of the products following the reaction.
Example: Calcium Chloride (CaCl2)
Calcium atomic mass = 40 a.m.u.
Chlorine atomic mass = 35 a.m.u. (x2)
40 + (35 x 2 atoms) = 110 a.m.u.
Certain chemicals, like strong acids and bases, are just not made to be mixed together (by sane people), unless under highly controlled conditions.
A + B g AB
A decomposition reaction is where 1 reactant will break down into 2 or more products.
AB g A + B
Example: burning, pocket hand warmers, glowsticks, batteries, electric eels
Example: chemical cold pack
Ex: lemon juice on an apple, food preservatives, CO2
on a fire, cooling Luminol
Write a balanced chemical equation for this reaction.