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Unit 8:� Covalent Compounds�College-Prep/Honors Chemistry

Make a copy of the packet and slideshow found on Google Classroom.
Discuss the Cicero quote from the front cover of your unit packet. Who have you seen embody this quote?

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Types of Bonding:

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Properties of Ionic Compounds

High Melting and Boiling Points:

A large amount of energy is needed to break the crystal lattice.

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Properties of Ionic Compounds

Hard and brittle:

Strong bonds make ionic substances rigid.
If struck, like ions (+ and +) are forced together and repel.
Analogy: Legos are hard, but brittle.

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Properties of Ionic Compounds

Many are soluble in water:

Water molecules surround ions, separate them, and prevent ions from attracting.

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Properties of Ionic Compounds

Conductive when dissolved or melted.

Ions are free to move and carry electrical charge.

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Properties of Covalent Compounds

Molecules vs. Formula Units:

Molecules (covalent) exist as separate units.

Formula units (ionic) are part of a larger crystal lattice.

1 formula unit of NaCl

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Properties of Covalent Compounds

Low melting points and boiling points:

Weak forces of attraction between molecules are broken (intramolecular forces– bonds within molecules aren’t broken)

ball pit analogy

Compound	Bonding	M.P. (˚C)	B .P. (˚C)
TiO₂	ionic	1843	2972
SO₂	covalent	–72	–10

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Properties of Covalent Compounds

Polarity and Solubility:

Polar solids and liquids are generally soluble/miscible in water.

Nonpolar solids and liquids are generally not soluble/immiscible in water.

cyclohexane

glucose

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Properties of Covalent Compounds

Generally nonconductive when dissolved in water.

There are no free ions able to carry the current through the sample.

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Demo: Conductivity of Aqueous Salt and Sucrose Solutions

Link to the demonstration will be posted here when it is ready: https://youtu.be/nZxEzpena20?si=LuB9-UrGNCHx6nMo&t=1221

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Demo: Conductivity of Aqueous Salt and Sucrose Solutions

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Naming Ionic Compounds Review

How do you name the following ionic compounds?

NaI
CaCl₂
Mg(NO₃)₂
Fe₂O₃
CuSO₄

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Naming Ionic Compounds Review

How do you name the following ionic compounds?

NaI	sodium iodide
CaCl₂	calcium chloride
Mg(NO₃)₂	magnesium nitrate
Fe₂O₃	iron(III) oxide
CuSO₄	copper(II) sulfate

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Naming Covalent Compounds

What is the chemical formula for sulfur oxide?

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Naming Covalent Compounds

What is the chemical formula for sulfur oxide?

S^2-and O^2-

If you think of these atoms as ions, there is no way to come up with a balanced chemical formula since both ions would be negative. They can’t both steal electrons to become negative. They don’t exchange electrons (ionic), but they share electrons (covalent). You wouldn’t know the ratio of S’s to O’s unless the chemical name indicates it. There are lots of options. SO₂ is sulfur dioxide. SO₃ is sulfur trioxide. S₂O₅ is disulfur pentoxide. Covalent compound names NEED prefixes.

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Prefixes

What are the prefixes for the numbers 1-10?

1	6
2	7
3	8
4	9
5	10

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Prefixes

What are the prefixes for the numbers 1-10?

1 mono (not used for the first element)	6 hexa
2 di	7 hepta (septa)
3 tri	8 octa
4 tetra (quad)	9 nona
5 penta	10 deca

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Naming Inorganic Covalent Compounds

Inorganic covalent compounds are compounds that contain only nonmetals but do not contain both carbon and hydrogen. Compounds that contain carbon AND hydrogen are organic compounds and the naming system is significantly different than that presented below.
Here are some examples of inorganic compounds that you may have seen before:

CO₂ carbon dioxide
CO carbon monoxide
H₂O dihydrogen monoxide, better known as water. Watch out for the DHMO conspiracy. https://www.dhmo.org/

The rule for naming covalent compounds is as follows:

(prefix) name of first element (prefix) name of 2nd element with ending changed to -ide. The final "o" or "a" of a prefix is often dropped when the element begins with a vowel.

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Naming Inorganic Covalent Compounds

Examples

N₂O₅
NO₂
SO₃
NO
P₂O₃
SF₆
CCl₄

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Naming Inorganic Covalent Compounds

Examples

N₂O₅ dinitrogen pentoxide
NO₂ nitrogen dioxide
SO₃ sulfur trioxide
NO nitrogen monoxide
P₂O₃ diphosphorus trioxide
SF₆ sulfur hexafluoride
CCl₄ carbon tetrachloride

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Opening Activity

Bring Your p.9 homework to the front.

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7—3 Practice Problems

1) silicon dioxide (sand)

3) phosphorus trichloride

5) silicon tetrafluoride

7) dinitrogen monoxide (NOS)

9) sulfur trioxide

11) dinitrogen pentoxide

13) iodine pentafluoride

15) sulfur hexafluoride

17) chlorine dioxide

19) tetraphosphorus trisulfide

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7—3 Practice Problems

2) nitrogen monoxide

4) sulfur tetrafluoride

6) xenon tetrafluoride

8) antimony pentafluoride

10) nitrogen trihydride (ammonia)

12) sulfur dioxide

14) dihydrogen monoxide (water)

16) carbon disulfide

18) carbon tetraiodide

20) boron trichloride

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7—3 Review and Reinforcement

Covalent Compounds

sulfur dioxide
hydrogen monoiodide
diphosphorus trisulfide
nitrogen trifluoride
sulfur hexafluoride
dihidrogen monosulfide
dinitrogen pentoxide
phosphorus pentachloride

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Ionic Compound or Covalent Compound?�(Formula Unit or Molecule?)

NF₃
CaF₂
P₂S₃
H₂S
(NH₄)₃PO₄
K₂CO₃

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Ionic or Covalent?�(Formula Unit or Molecule?)

NF₃ Covalent (molecules)
CaF₂ Ionic (formula units)
P₂S₃ Covalent (molecules)
H₂S Covalent (molecules)
(NH₄)₃PO₄Ionic (formula units)
K₂CO₃Ionic (formula units)

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Chemical Bonds

A bond is formed when two atoms exchange or share electrons.

An ionic bond is formed from the exchange of electrons.

A covalent bond is formed from the sharing of electrons.

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Chemical Bonds

Atoms exchange or share electrons to fill their outer orbitals.

Most atoms in Chemistry I want 8 valence electrons (octet rule).

Hydrogen and helium want 2 valence electrons (duet rule).

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Covalent Bond

A single covalent bond is a sharing of two electrons.

A double covalent bond is a sharing of four electrons.

A triple covalent bond is a sharing of six electrons.

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Valence Electrons

for hydrogen?

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Valence Electrons

for carbon?

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Valence Electrons

for oxygen?

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Valence Electrons

for nitrogen?

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Valence Electrons

for chlorine?

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Valence Electrons

for calcium?

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Valence Electrons

for selenium?

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Valence Electrons (Key)

for hydrogen? 1 (column 1)
for carbon? 4 (column 14)
for oxygen? 6 (column 16)
for nitrogen? 5 (column 15)
for chlorine? 7 (column 17)
for calcium? 2 (column 2)
for selenium? 6 (column 16)

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Lewis Dot Structure Examples

PO₄^3-

C₃H₈

CO₂

H₂O

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Covalent Bond: Lewis Dot Diagrams

1) Count the total number of valence electrons for each atom in the molecule.

H₂S

HPO₄^2– Anions get extra electron(s)

NH₄⁺ Cations get less electron(s)

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Covalent Bond: Lewis Dot Diagrams

2) Create the starting structure by using single bonds.

A single bond counts as 2 shared electrons.
For inorganic covalent compounds, the central atom is usually the first atom in the formula (except H).
For organic covalent compounds, form a carbon chain (backbone) to connect the carbon atoms.

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Covalent Bond: Lewis Dot Diagrams

3) Follow the octet rule (8 electrons).

Start with the outer atoms.
Hydrogen will only ever get 1 bond or 2 electrons (duet rule).

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Covalent Bond: Lewis Dot Diagrams

3C) Recount the number of valence electrons in your picture and place leftover electrons on the central atom.

3D) If you have used all of your electrons and some atoms still do not follow the octet rule, move a lone pair(s) of electrons to form a double or triple bond(s) may be necessary.

3E) Starting in energy level 3, elements may start to exceed the octet rule.

3F) Recount the number of valence electrons in your picture to make sure it contains the correct number.

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Covalent Bond: Lewis Dot Diagrams

4) Determine the formal charge for each atom by subtracting [the number of unshared electrons and half of the shared electrons] from the number of valence electrons.

Cliff Notes = V.E. – dots - bonds

Try to minimize the formal charge on each atom if possible without breaking the octet rule for atoms. in energy levels 1&2.

Charge

1-

Formal

Charge

-1

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Covalent Bond: Lewis Dot Diagrams

1-4) VE.SS.O.F

~5) Show resonance of double and triple bonds if possible.

~6) Show a bond dipole if the bond is polar.

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Lewis Dot Structure Examples

PO₄^3-

C₃H₈

CO₂

H₂O

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Opening Activity

Show me your 12 Lewis dot structures from pages 2-3 of the Molecular Modeling activity.
Groups 1-6 will draw their Lewis dot structure (with work) up on the board under their number.

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Lewis Dot Structure “Rules”

1) Total valence electrons (dots)

2) Central atom, single bonds

3) Octet Rule (H only gets 1 bond)

4) Extra dots? Out of dots: Double/Triple bonds?

5) Formal Charge

6) Resonance of double bonds

7) Bond dipole

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Opening Activity

Show me your last 6 Lewis dot structures from page 4 of the Molecular Modeling Activity (13-18).
Draw your group’s Lewis dot structure on the board.

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Opening Activity

Show me your 18 Ball and Stick Models

Mr. Mount’s and Mr. B’s Ice Bucket Challenge

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Opening Activity

Show me your completed Molecular Modeling post-lab.
Complete slide 23 (PF₃).

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Show me your Molecular Modeling Postlab.�Covalent Quiz Review

PF₃

Covalent or Ionic?
Name?
Molecule or Formula Unit?
Draw the Lewis Dot Structure

Show me your Molecular Models (1-12).

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Covalent Quiz Review

PF₃

Covalent or Ionic?

Name? phosphorus trifluoride

Molecule or Formula Unit?

Draw the Lewis Dot Structure

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Molecular Models�Question #1

VSEPR: Valence Shell Electron Pair Repulsion Theory

Model used to predict the shape of simple molecules.
Electron pairs will repel each other in a molecule
Molecules will seek a shape where electron pair repulsions is minimized.

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Molecular Models Question #1

What’s VSEPR Theory?

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Question #2

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Question #3

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Question #3

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Question #4

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Question #4

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Question #5

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Question #5

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Question #6

Space-filled model

Ball and stick model

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Question #7 2019-2020

wire-frame model

space-filled model

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Catalase Enzyme

protein chain

ribbon

protein chain

c-alpha trace

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Question #8

CH₃OH: 142 pm

H₂CO: 122 pm

CO₂: 120 pm

CN^-: 111 pm

CO: 106 pm

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Other structural formulas

We often don’t draw carbon atoms or hydrogen atoms. Carbon atoms are found at the end of every unlabeled line. Hydrogen atoms are attached so that every carbon atom gets four bonds. If atoms like oxygen don’t have an octet, they have lone pairs of electrons that haven’t been drawn.

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Other structural formulas

We often don’t draw carbon atoms or hydrogen atoms. Carbon atoms are found at the end of every unlabeled line. Hydrogen atoms are attached so that every carbon atom gets four bonds. If atoms like oxygen don’t have an octet, they have lone pairs of electrons that haven’t been drawn.

C₁₂H₂₂O or C₁₂H₂₁OH

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Other structural formulas

We often don’t draw carbon atoms or hydrogen atoms. Carbon atoms are found at the end of every unlabeled line. Hydrogen atoms are attached so that every carbon atom gets four bonds. If atoms like oxygen don’t have an octet, they have lone pairs of electrons that haven’t been drawn.

The smell of rain: What is the molecular formula of each?

C₁₂H₂₂O or C₁₂H₂₁OH

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Other structural formulas

palmitic acid

stearic acid

C₁₂H₂₂O or C₁₂H₂₁OH

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Other structural formulas

palmitic acid

stearic acid

C₁₂H₂₂O or C₁₂H₂₁OH

C₁₆H₃₂O₂ or C₁₅H₃₁COOH

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Other structural formulas

palmitic acid

stearic acid

C₁₂H₂₂O or C₁₂H₂₁OH

C₁₆H₃₂O₂ or C₁₅H₃₁COOH

C₁₈H₃₆O₂ or C₁₇H₃₅COOH

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Structural Formula for Diethyl Ether�(aka the ether bunny)

1) How many carbon atoms?

2) How many hydrogen atoms?

3) What is the complete chemical formula? (C_xH_yA_xB_xC_x)

4) How many lone pairs of electrons on the oxygen atom?

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Structural Formula for Diethyl Ether�(aka the ether bunny)

1) How many carbon atoms?

4

2) How many hydrogen atoms?

10

3) What is the complete chemical formula? (C_xH_yA_xB_xC_x)

C₄H₁₀O

4) How many lone pairs of electrons on the oxygen atom?

2

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Structural Formula for Cysteine:�My Best Attempt At A Michelangelo

1) How many carbon atoms?

2) How many hydrogen atoms?

3) What is the complete chemical formula? (C_xH_yA_xB_xC_x)

4) How many total lone pairs of electrons?

5) How many total double bonds?

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Structural Formula for Cysteine:�My Best Attempt At A Michelangelo

How many carbon atoms?

6

2) How many hydrogen atoms?

12

3) What is the complete chemical formula? (C_xH_yA_xB_xC_x)

C₆H₁₂N₂O₄S₂

4) How many total lone pairs of electrons?

14

5) How many total double bonds?

2

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Structural Formula for Vitamin C�(ascorbic acid)

1) How many carbon atoms?

2) How many hydrogen atoms?

3) What is the complete chemical formula? (C_xH_yA_xB_xC_x)

4) How many total lone pairs electrons?

5) How many total double bonds?

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Structural Formula for Vitamin C�(ascorbic acid)

Show me your Lewis dot structures from pages 21-23.

1) How many carbon atoms?

6

2) How many hydrogen atoms?

8

3) What is the complete chemical formula? (C_xH_yA_xB_xC_x)

C₆H₈O₆

4) How many total lone pairs electrons?

12

5) How many total double bonds?

2

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Structural Formula for Lactic Acid: �Feel the Burn!

Show me your p.11-12 VSEPR problems

1) How many carbon atoms?

2) How many hydrogen atoms?

3) What is the complete chemical formula? (C_xH_yA_xB_xC_x)

4) How many total lone pairs of electrons?

5) How many total double bonds?

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Structural Formula for Lactic Acid:�Feel the Burn!

1) How many carbon atoms?

3

2) How many hydrogen atoms?

6

3) How many total lone pairs of electrons?

6

4) How many total double bonds?

1

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Opening Activity

Show me your Lewis dot structures and formal charges from pages 19-20.
Quietly check your work with your small group members.

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Opening Activity

Show me your Lewis dot structures and formal charges from pages 26-28.
Quietly check your work with your small group members.

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Hold graphic organizer horizontally.

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Fold the bottom up to the # of electron domains.

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Fold in half horizontally.

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Fold in half horizontally a second time.

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Fold in half horizontally a third time.

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Unfold and cut down the creases.

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VSEPR Model: because electrons are negative, they will repel and move as far apart as possible.

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Electron-domain repulsions and the five basic shapes.

linear

trigonal planar

tetrahedral

trigonal bipyramidal

octahedral

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1 Electron Domain: 1 Molecular Shape

Examples: H_{2 ,}HCl, HF

Domain Shape: Linear

AX

molecular shape:

central atom

atom

lone pair of electrons

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2 Electron Domains: 1 Molecular Shape

Examples: CS₂, HCN, BeF₂

central atom

atom

lone pair of electrons

Domain Shape: Linear

molecular shape:

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3 Electron Domains: 2 Molecular Shapes

Examples: SO₂, O₃, PbCl₂, SnBr₂

Domain Shape:

molecular shape:

Examples: SO₃, BF₃, NO₃^-, CO₃^2-

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4 Electron Domains: 3 Molecular Shapes

Domain Shape:

molecular shape:

Examples:

NH₃

PF₃

ClO₃

H₃O⁺

Examples:

H₂O

OF₂

SCl₂

Examples:

CH₄

SiCl₄

SO₄^2-

ClO₄^-

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5 Electron Domains: 4 Molecular Shapes

Domain Shape:

molecular shape:

Examples:

PF₅

AsF₅

SOF₄

Examples:

ClF₃

BrF₃

Examples:

XeF₂

I₃^-

IF₂^-

molecular shape:

Examples:

SF₄

XeO₂F₂

IF₄⁺

IO₂F₂^-

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6 Electron Domains: 3 Molecular Shapes

Examples:

XeF₄

ICl₄^-

Domain Shape:

molecular shape:

Examples:

SF₆

IOF₅

molecular shape:

Examples:

BrF₅

TeF₅^-

XeOF₄

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Cisplatin

Important chemotherapy drug.

http://en.wikipedia.org/wiki/Cisplatin

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Opening Activity

Bring your p.19-20 VSEPR HW to the front.
Quietly review your answers with your small group members.

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Figure 8.8 The Pauling Electronegativity (EN) Scale

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Electronegativity Difference

Na—Cl

H—O

C—H

0.0 Nonpolar Covalent	≤ ~2.0 Polar Covalent	~ ≥ 2.0 Ionic

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Electronegativity Difference

Na—Cl 3.16-0.93 = 2.23 (ionic bond)

H—O 3.44-2.20 = 1.24 (polar covalent bond)

C—H 2.55-2.20 = 0.35 (slightly polar covalent bond)

0.0 Nonpolar Covalent	≤ ~2.0 Polar Covalent	~ ≥ 2.0 Ionic

The electronegativity values are found on the class periodic table. When finding the difference between two numbers, you are really finding the distance between the two numbers on a number line. You always subtract the smaller number from the bigger number to get a positive answer. With subtraction, the order of the numbers matters. Three minus five equals negative two [ 3-5 = -2 ], whereas five minus 3 equals positive two [5-3 = 2 ].

For H₂O, you would find the electronegativity difference between one H and one O, 1.4. Since the other O-H bond is identical, you would only have to calculate the difference once. The same applies to methane (CH₄). You would find the electronegativity difference between one C and one H, 0.4. Since the other three C-H bonds are identical you would only have to calculate the electronegativity difference once.

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Bond Polarity

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Electronegativity Difference

Na—Cl

H—O

C—H

an arrow is used to show a transfer of electrons for ionic bonds
A bond dipole arrow is used to show how the electrons are pulled closer to the more electronegative atom in a polar covalent bond

Na

Cl

[Cl]^-

[Na]⁺

Since NaCl is ionic, you would show the transfer of electrons like we did in Unit 6 when drawing ionic Lewis dot structures. Since H-O is polar, you will draw a bond dipole (sounds like die pole). The arrow points toward the oxygen because the oxygen is more electronegative and pulls the electrons more. This makes the oxygen partially negative. The hydrogen end of the bond is partially positive, as indicated by the positive sign on the dipole. The C-H bond is fairly nonpolar, so it will not have a bond dipole.

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Molecular Polarity

If a molecule has polar bonds, it will generally be a polar molecule.
If a molecule has nonpolar bonds, it will generally be a nonpolar molecule.
If all of the bond dipoles in a molecule point in equal and opposite directions, then a molecule with polar bonds may end up being nonpolar.

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Opening Activity

Bring your p.13-14 Polarity HW (1-7) to the front.
Quietly review your answers with your small group members.
Would ozone (O₃) be a polar molecule or a nonpolar molecule?

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Ozone (O₃)

Are the O-O bonds in ozone polar or nonpolar?
Would you expect the ozone molecule to be polar or nonpolar?

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Ozone (O₃)

Does the MEP model below change your answer?
Ozone is actually POLAR! The lone pair of electrons on the central oxygen causes an unequal distribution of electrons, which is the definition of a polar molecule.

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Why do we care about polarity?

Polarity determines what type of intermolecular forces molecules will experience (more slides to follow ☺)

This affects properties like boiling point, melting point, surface tension, cohesion, adhesion, vapor pressure, etc.

Polarity determines whether substances will dissolve or mix.

If two things have the same polarity they will dissolve each other or mix.

Polar substances dissolve/mix with polar substances.
Nonpolar substances dissolve/mix with nonpolar substances.

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Figure 10.14

The orientation of polar molecules in an electric field.

Electric field OFF

Electric field ON

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Opening Activity: C.P.

Copy the new EQ and answer the old EQ.
Bring your p.21-22 Polarity HW to the front.
Quietly review your answers with your small group members.

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Opening Activity: Honors

Bring your p.26-27 (1-7) Polarity HW to the front.
Quietly review your answers with your small group members.

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Intermolecular Forces

Can you think of any other words starting with the prefix “inter”?
Based on those words, what do you think “inter” means?
Based on this discussion, what do you think intermolecular forces are?
Intermolecular forces: the attractive forces between molecules. They cause molecules to stick to other molecules. There are three types: dispersion forces, dipole-dipole forces, and hydrogen bonds.

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Br—Br Br—Br�Dispersion forces

Some textbooks refer to these as London dispersion forces.
What does the word disperse mean?
If these intermolecular forces disperse after they form, do you think they would be strong or weak?
Dispersion forces: Since electrons constantly move, they might be closer to one atom in the bond for a split second. This causes the weak, temporary intermolecular forces between molecules. All molecules experience these temporary attractions. That’s why the dipoles attractions are dotted. This is the only type of attraction that exists between nonpolar molecules.

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S—F S—F�Dipole-Dipole Forces

What do you think a molecule needs to experience dipole-dipole forces?
The positive end of one molecule’s dipole will be attracted to which end of another molecule’s dipole?
Dipole-Dipole forces: the strong, permanent intermolecular forces between polar molecules.

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What’s Happening?

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What’s Happening?

Hydrogen Bonding

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H—N H—N�Hydrogen-bond

This term is misleading because a hydrogen bond is not really a bond; it’s a really strong intermolecular force involving hydrogen.
It’s similar to a dipole-dipole attraction, but it’s not the same. Molecules with H-bonding will also have dipole-dipole attractions.
Hydrogen bonding only involves molecules with an H—F bond, H—N bond, or H—O bond.
F, N, and O all have lone pairs of electrons which are negative. Since they have high electronegativities, the H in these bonds is extra positive.
Since F, N, and O are extremely small atoms, H can get really close to them.
This extremely positive H will be super strongly attracted to the lone pairs of electrons on the F, N, and O.

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Opening Activity: CP

Bring p.23 Polarity and your Polarity Prelab (page 1) to the front to receive credit.
Copy the new EQ and answer the old EQ
Quietly continue working on the prelab.

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Polarity Lab, Day 2

Pick up a pair of safety glasses and a lab apron from your assigned lab station.
If you know anything about the graffiti vandalism at Lab Station #1, I would appreciate if you share what you know with me.
Begin working on the lab.

Don’t forget to return your apron to your assigned lab station.
Discussion questions and NU conclusion due Monday.

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Polarity Lab

If you were absent, put on a pair of goggles and apron and begin working on the Polarity Lab.
If you were here Friday, show me your completed Polarity Lab for credit.
Quietly discuss the discussion questions in your small groups.
Pick up a clicker and a periodic table

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DNA: A–T and G–C

Why do adenine and thymine always pair?

T – A

Why do guanine and cytosine always pair?

C – G