Lewis Dot

Lewis DotTypes of Bonds

A. Electronegativity - The ability of an atom to attract electrons to itself in a bond

1. Periodic Trends (link to size)Metals – Low ElectronegativityNon- Metals – High Electroneg

The smaller the atom, the higher the electronegativity

Lewis DotIonic vs. Molecular Compounds

Ionic Compounds Molecules

Metal + Non-MetalStealing of ElectronsCalled SaltsClumps of Ions

No prefixes, may need Roman #

Two Non-metalsSharing of electrons (Covalent or Polar Cov.)Separate MoleculesPolar and Non-Polar Molecules (H2O vs CH4)

Prefixes

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Lewis DotTypes of Bonds

3. Types of bondsElectroneg. Difference

Ionic >2Polar Cov. 0.2 – 1.9Covalent <0.2

Example: Li - F

Lewis Dot

Which of the following form predominantly ionic, covalent, or polar covalent bonds?

B-Cl P-H

Na-F P-Cl

C-Cl O-H

Lewis DotL. Dot for Ionic Compounds

Why do Ionics steal? To gain an Octet

Draw Lewis Dot Pictures for:

NaCl

CaCl2

BaO

Li2O

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Lattice Energy – Energy required to convert a mole of an ionic solid to its gaseous ions

NaCl(s) Na+(g) + Cl-(g)

• Increases as distance (d) decreases

• Increases with increasing charge (Q)

U = k Q1Q2

d

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Melting Point and Charge

MgCl2 MgO

(778 oC) (2800 oC)

CaCl2 CaO

(772 oC) (2528 oC)

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Which would have a higher lattice energy?

a. NaCl or KCl

b.CaBr2 or Ca3N2

c. NaCl or NaBr

d.CaI2 or CaO

Lewis DotOld School Lewis Dots

Molecular Compounds

CH4 CO2 C2H4

H2O HCN C2H2

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Michael Faraday's Benzene Sample (1825)

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The Lone Pear(Pair) rides again!

Lewis DotLewis Dots

Rules1. Sum all valence electrons, including

charges2. Single Bonds3. Outer atoms get an octet except H4. Center gets rest even if it violates the octet5. Double/triple bonds if center atom still

does not have an octet

Lewis DotLewis Dots

NH3

NCl3

SF6

CO2

HCN

ClF5

Lewis DotLewis Dots

You try:

SF4

H2SO4

KrF4

Cl2O

NH2CH3

Lewis DotsCH3CH2CHCH2

CHCCH2NCl2

Lewis DotLewis Dots

CN-

ICl4-

BrO3-

NO+

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You try:

CO32-

IBr4-

BF4-

SO42-

Lewis DotResonance Structures

Warm-Up: O3

Definition – When a molecule can exist in more than one arrangement of electrons

1. Atoms remain static

2. Only the electrons move

Resonance StructuresExamples

NO2- CHO2

- HNO3

Which needs resonance, SO3 or SO32-

Order the species in the previous problem from shortest to longest bond length.

Resonance Structures Benzene

SO2

SO22-

Lewis DotLess Than an Octet

• Hydrogen Only gets 2

• Beryllium, Boron, and Aluminum

BeCl2 BF3 AlF3

Lewis DotMore Than an Octet

• Just follow the rules and you will be able to draw these

• Ex: AsF6-

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Lewis DotStrengths of Covalent Bonds

Single < Double < Triple

Bond Strength (kJ/mole)

Bond Length(Å)

C-C 348 1.54

C=C 614 1.34

C = C 839 1.20

N = N 941 1.10

Lewis DotCalculating Enthalpies of Reaction

Hrxn = Hbroken – made

Calculate the heat of reaction for the following reaction.

CH4(g) + Cl2(g) CH3Cl(g) + HCl(g)

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Let’s look at bonds broken and made

H-CH3 + Cl-Cl Cl-CH3 + H-Cl

Bonds broken: One mol C-H, One mol Cl-Cl

Bonds made:One mol C-Cl, One mol H-Cl

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Hrxn = Hbroken – made

Hrxn = [1(C-H) + 1(Cl-Cl)] – [1(C-Cl) + 1(H-Cl)]

Hrxn = [413 kJ + 242 kJ] – [328 kJ + 431 kJ]

Hrxn = -104 kJ (Exothermic reaction)

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Calculate the H for the following reaction:

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Bonds Broken Bonds Made

6 C-H 4 C=O

1 C-C 6 O-H

7/2 O2

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Hrxn = Hbroken – made

Hrxn = [6C-H + 1C-C + 7/2O2] – [4C=O + 6O-H]

Hrxn = [6(413) + 1(348) + 7/2(495)]

– [4(799) + 6(463)]

Hrxn = -1416 kJ (Exothermic reaction)

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Calculate the H for the following reaction:

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Bonds Broken Bonds Made

4 N-H 1 N=N

1 N-N 2 H-H

Hrxn = Hbroken – made

Hrxn = [4N-H + 1 N-N] – [1 N=N + 2 H-H]

Hrxn = [4(391) + 1(163)] – [1(941) + 2(436)]

Hrxn = -86 kJ (Exothermic reaction)

Lewis DotDouble Bonds

Calculate the enthalpy change for the following reaction. Be sure to always break the multiple bond and remake a single C-C bond.

Br Br

| |

H-C=C-H + Br2 H-C-C-H

| | | |

H H H H

(ANS: -93 kJ)

Lewis DotDouble Bonds

Calculate the enthalpy change for the following reaction.

H H

| |

H-C=C-H + 2H2 H-C-C-H

| |

H H

(ANS: -289 kJ)

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If the enthalpy change for the following reaction is 0 kJ, calculate the C-Cl bond energy.

CH3Cl(g) + H2O(g) CH3OH(g) + HCl(g)

Bond energy

H-Cl 430 kJ/mol

C- O 360 kJ/mol

O-H 460 kJ/mol

(ANS: 330 kJ/mol)

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If the enthalpy change for the following reaction is -1995 kJ, calculate the bond energy of C=O.

C3H8(g) + 5O2(g) 3CO2(g) + 4H2O(g)

Bond energy

C-C 345 kJ/mol

C-H 415 kJ/mol

O2 495 kJ/mol

O-H 460 kJ/mol (800 kJ)

SuffixOrganic Naming

Suffix Class Characteristic

-ane Alkane All single bonds

-ene Alkene Double bond(s)

-yne Alkynes Triple bond(s)

IUPAC Names of Alkanes

# of C atoms

Name & Formula # of C atoms

Name & Formula

1 Methane CH46 Hexane C6H14

2 Ethane C2H67 Heptane C7H16

3 Propane C3H88 Octane C8H18

4 Butane C4H109 Nonane C9H20

5 Pentane C5H1210 Decane C10H22

Suffix = -ane

Name the following and write the chemical formula

Lewis Dot14. [Ca]2+2[F]- (8 ve- around F)

16. BaF2 CsCl Li3N Al2O3

20 a) KF has a larger LE because F- is much smaller than Cl-

b) Na – Cl ~ 2.8 A K-F ~ 2.7A

22. a) (i) Increases with charge (ii) decreases with d

b) KBr < NaF < MgO < ScN

24 a) Ca2+ is smaller than Ba2+, higher LE

b) NaCl is smallest pair, highest LE

c) BaO has highest charges, highest LE

Lewis Dot34. a) Draw LD of H2O2 and O2

b) O2 has a double bond, shorter bond length

38. a) O b) Al c) Cl d) F

40. a) O-F < C-F < Be-F

b) S-Br < C-P < O-Cl

c) C-S < N-O < B-F

Lewis Dot50.Bond Length SO2 < SO3 < SO32-

52. CO2 (no resonance needed)

54. Bond Length NO+ < NO2- <NO3

-

66. a) -104 kJ b) 20 kJ c) 5 kJ

68. a) -2023 kJ b) -1255 kJ c) -192 kJ

70. a) -124 kJ b) -137 kJ

1. a) C2H3Cl3O2 b) Same

Lewis Dot62.

100. In2S (I) [Kr]5s24d10

InS (II) [Kr]5s14d10

In2S3 (III) [Kr]4d10

In(III) is smallest (least mutual electron repul)

In(III) has the highest lattice energy

102.a) C2H3Cl3O2 b) C2H3Cl3O2

c) Structure CCl3CH(OH)2

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