Post on 18-Jan-2022
4/29/2015
1
UNIT 17Review, Part IVLewis, IMF, Bonding, Acid-Base, Solutions
Molecular Compounds:
Are made of nonmetalsNonmetals have high
electronegativity, so they do NOT release their electrons.
Two nonmetals share some of their valence electrons (in bonds) to achieve full octets.
The atoms are CO-valent-ly bonded!
Shared Valence
4/29/2015
2
Molecular GeometryGeometry = shapesVSEPR Theory
ValenceShellElectronPairRepulsionAKA: electrons hate each other
VSEPR TheoryThe electrons interacting in molecules (valence
shell electron pairs)Are REPULSED by each other.The electron pairs around the central atom orient
themselves as far apart as possible– in order to minimize their mutual repulsion.
4/29/2015
4
H Cl+ -
Assume ALL bonds are polar unless the same element is on both ends!
N2, O2, & F2 are made of nonpolarbonds.
So are N3 & O3
I. Lewis Dot Structures
NH3
N
H
HH C OOO HH
H2O
C
H
HHH
CH4 CO2
All of these bonds are polar.
4/29/2015
5
I. Lewis Dot Structures
N3
N NN OOHH
H2
ClCl
Cl2 O2
All of these bonds are nonpolar.
The bonds are all polar. Is the MOLECULE Polar?
NH3
N
H
HH C OOO HH
H2O
C
H
HHH
CH4 CO2
POLAR POLARNONPOLAR NONPOLAR
4/29/2015
6
This ATTRACTION
between the
molecules is the IMF.
The three IMFS:o London
Dispersiono Dipole-Dipoleo Hydrogen
BondingSTRONG
weak
4/29/2015
7
between temporary dipoles due to uneven e- dispersion
All atoms & molecules
Weakest strengthStronger for molecules with greater masses.
Instantaneous attraction
Charge attraction between permanent dipoles
All polar molecules
Medium strength
It is stronger when the molecules are closer.
4/29/2015
8
I. Lewis Dot Structures
NH3
N
H
HH C OOO HH
H2O
C
H
HHH
CH4 CO2
POLAR POLARNONPOLAR NONPOLAR
HIGHERmelting points
and boiling points
(dipole-dipole)
LOWERmelting points
and boiling points
(no dipole-dipole)
Extreme attraction between molecules with N-H, O-H, or F-H bonds.
Molecules with H bound directly to N, O, F
Greatest strengthSometimes called a “pseudo bond”, but it is NOT chemical bonding.
4/29/2015
9
Which ones exhibit hydrogen bonding?
NH3
N
H
HH C OOO HH
H2O
C
H
HHH
CH4 CO2
H-Bonding! H-Bonding!Nope Nope
4/29/2015
13
Nonmetals share because their electronegativities are too high to let any electrons go.
4/29/2015
14
Nonmetals share because their electronegativities are too high to let any electrons go.
• POLAR molecules are soluble in (polar) water.
• NON-polar molecules are insoluble.
4/29/2015
15
Metals release their valence electrons because their electronegativities are too low to hold on.
Metals release their valence electrons because their electronegativities are too low to hold on.
4/29/2015
16
Metals release their valence electrons
because their electronegativities are too low to hold on to them.
STRONGEST
WEAKEST
4/29/2015
17
C. Johannesson
ACID-BASEACID-BASE
electrolytes electrolytes
turn litmus red
sour taste
react with metals to form H2 gas
slippery to touch
turn litmus blue
bitter taste
ChemASAP
vinegar, milk, soda, apples, citrus fruits
ammonia, lye, antacid, baking soda
C. Johannesson
ACID-BASEACID-BASE
High H+ (H3O+) conc. High OH- conc.
turn litmus red
Low pH (<7)
Formula:
• begins with H
• ends with a NM
Formula (usually):
• begins with a M
• Ends with OH
turn litmus blue
High pH (>7)
ChemASAP
4/29/2015
18
C. Johannesson
B. DefinitionsB. Definitions
•Acids release hydrogen ions (H+)
•Acids create hydronium ions (H3O+)
H
HH H H
H
ClClO O
–+
acid hydronium
C. Johannesson
B. DefinitionsB. Definitions
•Bases form hydroxide ions (OH-)
H
H
HH H
H
N NO O
–+
H
H
H H
base hydroxide
4/29/2015
19
LPChem:Wz
B. pH CalculationsB. pH Calculations
pH
pOH
[H+](H3O+)
[OH-]
-log[H3O+]
-log[OH-]
10^(–pH)
10^(–pOH)
Kw = [H3O+][OH-] 14 = pH + pOH
_ 2 sig figs
C. Johannesson
B. pH ScaleB. pH Scale
What is the pH of 0.010 M HNO3?
pH = -log[H3O+]
pH = -log[0.010]
pH = 2.00
Acidic or basic? Acidic
__ 2 sig figs after the decimal
strong acid
pH < 7
4/29/2015
20
LPChem:Wz
B. pH ScaleB. pH Scale
What is the [H3O+] of a solution with pH = 7.45?
pH = -log[H3O+]
Therefore 10^ -pH = [H3O+]
10^ -7.45 = [H3O+]
= 3.6 x 10-8 M
LPChem:Wz
A. NeutralizationA. Neutralization
Chemical reaction between an acid
and a base.
4/29/2015
21
LPChem:Wz
A. NeutralizationA. Neutralization
Chemical reaction between an acid
and a base.
Products are a salt (ionic compound) and water.
A. NeutralizationA. Neutralization
ACID + BASE SALT + WATERHCl + NaOH NaCl + H2O
• Acid + Base = Salt + Water is a neutralization reaction.
• Titration is used to solve for an unknown concentration in acid-base neutralizations.
4/29/2015
22
C. Johannesson
B. TitrationB. Titration
moles H3O+ = moles OH-
MVn = MVnM: MolarityV: volumen: # of H+ ions in the acid
or OH- ions in the base
LPChem:Wz
B. TitrationB. Titration
10.0 mL of 2.3M LiOH are required to neutralize 20.0 mL of HNO2. Find the molarity of HNO2.
H3O+
M = ?
V = 20.0 mL
n = 1
OH-
M = 2.3M
V = 10.0 mL
n = 1
MV# = MV#(2.3M)(10.0mL)(1) =
M(20.0mL)(1)
M = 1.15M HNO2
4/29/2015
23
C. Johannesson
A. DefinitionsA. Definitions
Solution - homogeneous mixture
Solvent – the dissolver (present in greater amount)
Solute - substance being dissolved
LPChem:Wz
B. SolvationB. Solvation
StrongElectrolyte
Non-Electrolyte
Ionic compounds, Strong acids, Strong bases
Molecular substances
WeakElectrolyte
Weak acids & Weak bases
i = 1 i = 1 < i < 2i = 2 or more
4/29/2015
24
C. Johannesson
B. SolvationB. Solvation
NONPOLAR
NONPOLAR
POLAR
POLAR
“Like Dissolves Like”“Like Dissolves Like”
C. Johannesson
C. SolubilityC. Solubility
SATURATED SOLUTION
no more solute can dissolve
UNSATURATED SOLUTION
more solute can dissolve
SUPERSATURATED SOLUTIONUnstable.
crystals form if solute is added
concentration
4/29/2015
25
C. Johannesson
A. DefinitionA. Definition
Colligative Property
• property that depends on the concentration of solute
particles, not their identity
B. TypesB. Types
Freezing Point Depression (Tf)
• f.p. of a solution is lower than f.p. of the pure solvent
Boiling Point Elevation (Tb)
• b.p. of a solution is higher than b.p. of the pure solvent
Tb(normal) + Tb = Tb(elevated)
Tf(normal) - Tf = Tf(depressed)
LPChem:Wz