Review, Part IV ppt

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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

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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.

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I. Lewis Dot Structures

NH3

N

H

HH C OOO HH

H2O

C

H

HHH

CH4 CO2

polar

H Cl+ -

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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


NH3

N

H

HH C OOO HH

H2O

C

H

HHH

CH4 CO2

All of these bonds are polar.

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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

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This ATTRACTION

between the

molecules is the IMF.

The three IMFS:o London

Dispersiono Dipole-Dipoleo Hydrogen

BondingSTRONG

weak

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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.

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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.

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Which ones exhibit hydrogen bonding?

NH3

N

H

HH C OOO HH

H2O

C

H

HHH

CH4 CO2

H-Bonding! H-Bonding!Nope Nope

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stable (full octet!)

To get to the valence electron on the other side!

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Nonmetals share because their electronegativities are too high to let any electrons go.

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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.

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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.

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Metals release their valence electrons

because their electronegativities are too low to hold on to them.

STRONGEST

WEAKEST

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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

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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

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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

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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.

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LPChem:Wz


Chemical reaction between an acid

and a base.

Products are a salt (ionic compound) and water.


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.

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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

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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

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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

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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

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C. Johannesson

C. CalculationsC. Calculations

T: change in temperature (°C)

K: constant based on the solvent (°C·kg/mol)

m: molality (m)

i: ion number (# of particles)

T = K · m · i

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Review, Part IV ppt