unit 17 review, part iv lewis, imf, bonding, acid-base, solutions

UNIT 17Review, Part IVLewis, IMF, Bonding, Acid-Base, Solutions

Molecular Compounds:Are made of nonmetals

Nonmetals 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!

LPChem:W

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Shared Valence

Molecular GeometryGeometry = shapesVSEPR Theory

ValenceShellElectronPairRepulsion

AKA: electrons hate each other

LPChem: W

z Unit 12: M

olecular Structure

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.

Unit 12: M

olecular Structure

LPChem: W

z

I. Lewis Dot Structures

NH3

LPChem:W


NH

HH C OOO HH

H2O

CH

HHH

CH4 CO2

LPChem after JohannessonA. Polar Bonds

• A bond between atoms of two different elements tends to be polar.

• One end is slightly positive, the other is slightly negative.

H Cl+ -

LPChem after JohannessonA. Polar Bonds

H Cl+ -

Assume ALL bonds are polar unless the same element is on both ends!

N2, O2, & F2 are made of nonpolar bonds.

So are N3 & O3


NH3

LPChem:W


NH

HH C OOO HH

H2O

CH

HHH

CH4 CO2

All of these bonds are polar.


N3

LPChem:W


N NN OOHH

H2

ClCl

Cl2 O2

All of these bonds are nonpolar.

The bonds are all polar. Is the MOLECULE Polar?

NH3

LPChem:W


NH

HH C OOO HH

H2O

CH

HHH

CH4 CO2

POLAR

POLAR NONPO

LARNONPOLAR

Intermolecular Forces (IMFs)Intermolecular Forces = (Attraction) Forces between moleculesIMFs are much weaker than bonds

Unit 12: Molecular Structure

LPChem: W

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This ATTRACTI

ON between

the molecules is the IMF.

Intermolecular Forces (IMFs)Intermolecular Forces = (Attraction) Forces between moleculesIMFs are much weaker than bonds


LPChem: W

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The three IMFS:oLondon

DispersionoDipole-DipoleoHydrogen

Bonding STRONG

weak

London Dispersion:What is it?

Who has it?

How strong is it?

And?Unit 12: Molecular Structure

LPChem: W

z between temporary dipoles due to uneven e- dispersion

All atoms & molecules

Weakest strengthStronger for molecules with greater masses.

Instantaneous attraction

Dipole-Dipole Interaction:What is it?

Who has it?

How strong is it?


LPChem: W

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Charge attraction between permanent dipoles

All polar molecules

Medium strength

It is stronger when the molecules are closer.


NH3

LPChem:W


NH

HH C OOO HH

H2O

CH

HHH

CH4 CO2

POLAR

POLAR NONPO

LARNONPOLAR

HIGHER melting points

and boiling points

(dipole-dipole)

LOWER melting points

and boiling points

(no dipole-dipole)

Hydrogen Bonding:What is it?

Who has it?

How strong is it?


LPChem: W

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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.

Which ones exhibit hydrogen bonding?

NH3

LPChem:W


NH

HH C OOO HH

H2O

CH

HHH

CH4 CO2

H-Bonding!

H-Bonding!

Nope

Nope

Why are IMFs important?More IMFs make a substance “stick together” more. This increases:Melting & Boiling pointsCohesion


LPChem: W

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Surface Tension: the attractive force between particles in a liquid that minimizes surface area.

Why are IMFs important?

Capillary action: attractive force between the surface of a liquid and the surface of a solid


LPChem: W

z Polar substances also stick to other polar substances, leading to:

Mutual Solubility & Miscibility (dissolving & mixing together)

Why are IMFs important?Dissolving & mixing:Polar molecules (like water) are attracted to other polar molecules. They dissolve/mix together easily.


LPChem: W

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Nonpolar molecules (like oil) do not dissolve/mix with polar substances.

Chemical BondingWhy did the atom cross the road?

Remember: atoms make bonds in order to achieve a stable (full octet!) electron configuration.


LPChem: W

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To get to the valence electron on the other side!

Chemical Bonding:The three bond types are based on the different ways

atoms achieve a full octet:

IONIC

Transfer

Electrons

COVALENT

ShareElectron

s

METALLIC

Delocalize & PoolElectrons(electron sea)

Unit 12: Molecular Structure LPChem: Wz

Ionic Bonds: A transfer of one or more electrons from one atom to another. (Creating IONS.)Ionic formulas are always given empirically. (Smallest whole number ratio.)


LPChem: W

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Ionic Bonds: Structure:An ionic CRYSTAL Made of cations and anions(Opposites attract = ionic bonding)Arranged in a rigid checkerboard (lattice) structure


LPChem: W

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Ionic Bonds: The rigid checkerboard pattern gives ionic compounds their unique properties:BrittlenessNon-conductive solidsUsually water solubleConductive in (aq)Extremely high mp


LPChem: W

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Covalent Bonds: SHARING one or more pair of electrons between two atoms. (Creating molecules.)Molecule formulas are usually NOT given empirically.E.g., glucose is written C6H12O6 instead of C1H2O1


LPChem: W

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

Covalent Bonds: Structure:Individual MOLECULESHeld together in solid or liquid form by IMFs. (IMFs are weak compared to bonds, so these melt/boil easily.)


LPChem: W

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

Covalent Bonds: The fact that they form molecules why covalent compounds have these properties:Non-electrolytes (no conductivity in (s) or (aq))

Low melting/boiling points

Tendency to burn (decompose)

Aqueous solubility varies:


LPChem: W

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• POLAR molecules are soluble in (polar) water.

• NON-polar molecules are insoluble.

Metallic Bonds: Delocalizing and pooling electrons in the electron sea.The electrons are loose and can flow freely throughout the entire chunk of metal.


LPChem: W

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Metals release their valence electrons because their electronegativities are too low to hold on.

Metallic Bonds: Structure:A “crystal” made of metal CATIONSIn a sea of valence electronsWhich flow freely everywhere.


LPChem: W

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Metals release their valence electrons because their electronegativities are too low to hold on.

Metallic Bonds: The electron sea is what gives metals their characteristic properties:Malleability & ductilitySolid conductivityInsoluble in aqueousLusterRelatively high melting points


LPChem: W

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Metals release their valence electrons because their electronegativities are too low to hold on to them.

Relative bond strength: NP Covalent: equal electron SHARING (between similar nonmetals)Polar Covalent: unequal electron SHARING (between dissimilar nonmetals)Ionic: TRANSFER of electrons (from metal to nonmetal, creating ions)Metallic: ELECTRON SEA of delocalized electrons (between metals)


LPChem: W

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STRONGEST

WEAKEST

C. Johannesson

ACID-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-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

C. Johannesson

B. Definitions

• Acids release hydrogen ions (H+) • Acids create hydronium ions (H3O+)

H

HH H H

H

Cl ClO O–+

acid hydronium

C. Johannesson

B. Definitions• Bases form hydroxide ions (OH-)

H

H

HH H

H

N NO O–+

HH

H H

base hydroxide

LPChem:Wz

B. 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 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 [HNO3] = [H3O+]

pH < 7

LPChem:Wz

B. 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. NeutralizationChemical reaction between an acid

and a base.

LPChem:Wz

A. NeutralizationChemical reaction between an acid

and a base.Products are a salt (ionic compound)

and water.

A. 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.

C. Johannesson

B. Titration

moles H3O+ = moles OH-

MV n = MV nM: MolarityV: volumen: # of H+ ions in the acid

or OH- ions in the base

LPChem:Wz

B. Titration10.0 mL of 2.3M LiOH are required to

neutralize 20.0 mL of HNO2. Find the molarity of HNO2.

H3O+

M = ?V = 20.0 mLn = 1

OH-

M = 2.3MV = 10.0 mLn = 1

MV# = MV#(2.3M)(10.0mL)(1) =

M(20.0mL)(1)

M = 1.15M HNO2

C. Johannesson

A. Definitions

Solution - homogeneous mixture

Solvent – the dissolver (present in greater amount)

Solute - substance being dissolved

LPChem:Wz

B. 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

C. Johannesson

B. Solvation

NONPOLAR

NONPOLARPOLARPOLAR

“Like Dissolves Like”

C. Johannesson

C. Solubility

SATURATED SOLUTION

no more solute can dissolve

UNSATURATED SOLUTION

more solute can dissolve

SUPERSATURATED SOLUTIONUnstable.

crystals form if solute is added

concentration

C. Johannesson

A. Definition

Colligative Property• property that depends on the concentration of solute

particles, not their identity

B. 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

solventTb(normal) + Tb = Tb(elevated)

Tf(normal) - Tf = Tf(depressed)

LPChem:Wz

C. Johannesson

C. 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

unit 17 review, part iv lewis, imf, bonding, acid-base, solutions

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