This document discusses chemical bonding and Lewis structures. It defines different types of bonds including ionic bonds, covalent bonds, and polar covalent bonds. It provides examples of how to draw Lewis structures for atoms, molecules, and polyatomic ions. Rules for constructing Lewis structures are outlined. Resonance structures and exceptions to the octet rule are also covered. The document concludes with sections on electronegativity, dipole moment, molecular structure using VSEPR theory.

1. Types of chemical bondsTypes of chemical bonds
BondBond: Force that holds groups of two or more atoms: Force that holds groups of two or more atoms
together and makes the atoms function as a unit.together and makes the atoms function as a unit.
Example: H-O-HExample: H-O-H
Bond EnergyBond Energy: Energy required to break a bond.: Energy required to break a bond.
Ionic BondIonic Bond: Attractions between oppositely charged ions.: Attractions between oppositely charged ions.
Example: NaExample: Na++
ClCl--

2. Types of chemical bondsTypes of chemical bonds
Ionic CompoundIonic Compound: A compound resulting from a positive ion: A compound resulting from a positive ion
(usually a metal) combining with a negative ion (usually(usually a metal) combining with a negative ion (usually
a non-metal).a non-metal).
Example: MExample: M++
+ X+ X--
 MXMX
Covalent BondCovalent Bond: Electrons are shared by nuclei.: Electrons are shared by nuclei.
Example: H-HExample: H-H
Polar Covalent BondPolar Covalent Bond: Unequal sharing of electrons by: Unequal sharing of electrons by
nuclei.nuclei.
Example: H-FExample: H-F
Hydrogen fluoride is an example of a molecule that hasHydrogen fluoride is an example of a molecule that has
bond polarity.bond polarity.

3. Lewis structuresLewis structures
Lewis StructureLewis Structure: Representation of a molecule that shows: Representation of a molecule that shows
how the valence electrons are arranged among the atomshow the valence electrons are arranged among the atoms
in the molecule.in the molecule.
Bonding involves the valence electrons of atoms.Bonding involves the valence electrons of atoms.
Example: NaExample: Na●● H-HH-H

4. Lewis structures ofLewis structures of
elementselements
 Dots around elemental symbolDots around elemental symbol
– Symbolize valence electronsSymbolize valence electrons
 Thus, one must know valence electronThus, one must know valence electron
configurationconfiguration

6. Lewis Structures ofLewis Structures of
moleculesmolecules
Single BondSingle Bond: Two atoms sharing one electron pair.: Two atoms sharing one electron pair.
Example: HExample: H22
Double BondDouble Bond: Two atoms sharing two pairs of electrons.: Two atoms sharing two pairs of electrons.
Example: OExample: O22
Triple BondTriple Bond: Two atoms sharing three pairs of electrons.: Two atoms sharing three pairs of electrons.
Example: NExample: N22
Resonance StructuresResonance Structures: More than one Lewis Structure can: More than one Lewis Structure can
be drawn for a molecule.be drawn for a molecule.
Example: OExample: O

7. Rules for Lewis structures ofRules for Lewis structures of
moleculesmolecules
1.1. Write out valence electrons for each atomWrite out valence electrons for each atom
2.2. Connect lone electrons because loneConnect lone electrons because lone
electrons are destabilizingelectrons are destabilizing
1.1. Become two shared electronsBecome two shared electrons
1.1. Called a “bond”Called a “bond”
3.3. Check to see if octet rule is satisfiedCheck to see if octet rule is satisfied
1.1. Recall electron configuration resembling nobleRecall electron configuration resembling noble
gasgas
1.1. In other words, there must be 8 electrons (bonded orIn other words, there must be 8 electrons (bonded or
non-bonded) around atomnon-bonded) around atom
1.1. Non-bonded electron-pairNon-bonded electron-pair
1.1. Called “lone pair”Called “lone pair”

8. Let’s do some examplesLet’s do some examples
on the boardon the board
 HH22
– Duet ruleDuet rule
 FF22
– Octet ruleOctet rule
 OO22
 NN22

9. Lewis structuresLewis structures
ExampleExample
Write the Lewis Structure for the followingWrite the Lewis Structure for the following
molecules:molecules:
1)1) HH22OO
2)2) CClCCl44
1)1) Where does the carbon go & why?Where does the carbon go & why?
3)3) PHPH33
4)4) HH22SeSe
5)5) CC22HH66

10. Lewis structuresLewis structures
continuedcontinued
6)6) COCO22
7)7) CC22HH44
8)8) CC22HH22
9)9) SiOSiO22

11. Polyatomic ionsPolyatomic ions
 If positive charge on ionIf positive charge on ion
 Take away electron from central speciesTake away electron from central species
 If negative charge on ionIf negative charge on ion
 Add electron to central speciesAdd electron to central species
 Example:Example:
 HH33OO++

12. Your turnYour turn
 NHNH44
++
 ClOClO--
 OHOH--

13. Resonance structuresResonance structures
 When structures can be written inWhen structures can be written in
more than one waymore than one way
– OO33
 Actual molecule is “in-between”Actual molecule is “in-between”
– Resonance hybridResonance hybrid
 Another exampleAnother example
– HCOHCO33
--
 What would its resonance hybrid look like?What would its resonance hybrid look like?

14. PracticePractice
 NONO22
--
 NONO33
--

15. PracticePractice
 HH22OO22
 HH33OO++

16. Aberrant compoundsAberrant compounds
 Odd-electron speciesOdd-electron species
– NONO
– NONO22

17. Aberrant compoundsAberrant compounds
 Incomplete octetIncomplete octet
– BHBH33

18. Aberrant compoundsAberrant compounds
 Expanded octetExpanded octet
– Some central atoms can exceed an octetSome central atoms can exceed an octet
 Third period and higher elements canThird period and higher elements can
do thisdo this
– E.g., Al, Si, P, S, Cl, As, Br, Xe, etc.E.g., Al, Si, P, S, Cl, As, Br, Xe, etc.
– d-orbitals can accommodate extrad-orbitals can accommodate extra
electronselectrons

19. ExamplesExamples
 AsIAsI55
 XeFXeF22

20. PracticePractice
 SClSCl66
 XeFXeF44

21. PracticePractice
 SOSO33
2-2-
 POPO33
3-3-
 SOSO22
 SOSO33
 HH22SeOSeO44

22. ElectronegativityElectronegativity
ElectronegativityElectronegativity: The relative ability of an atom in a: The relative ability of an atom in a
molecule to attract shared electrons to itself.molecule to attract shared electrons to itself.
Example: Fluorine has the highest electronegativity.Example: Fluorine has the highest electronegativity.
 SimilarSimilar electronegativities between elements give non-electronegativities between elements give non-
polar covalent bonds (0.0-0.4)polar covalent bonds (0.0-0.4)
 DifferentDifferent electronegativities between elements giveelectronegativities between elements give
polar covalent bonds (0.5-1.9)polar covalent bonds (0.5-1.9)
 If the difference between the electronegativities of twoIf the difference between the electronegativities of two
elements is about 2.0 or greater, the bond is ionicelements is about 2.0 or greater, the bond is ionic

23. ElectronegativityElectronegativity
ExampleExample
For each of the following pairs of bonds,For each of the following pairs of bonds,
choose the bond that will be more polar.choose the bond that will be more polar.
 Al-P vs. Al-NAl-P vs. Al-N
 C-O vs. C-SC-O vs. C-S

24. Dipole momentDipole moment
 Dipole MomentDipole Moment
 A molecule that has a center of positiveA molecule that has a center of positive
charge and a center of negative chargecharge and a center of negative charge
 Will line up on electric fieldWill line up on electric field
 In Debye unitsIn Debye units
 1 D = 3.34 x 101 D = 3.34 x 10-30-30
CC •• mm

25. ExamplesExamples
 FF22
 COCO22
 HH22OO
 NHNH33
 BFBF33
 CClCCl44

26. Molecular polarityMolecular polarity
 Net-dipole moment leads to molecularNet-dipole moment leads to molecular
polaritypolarity
 Thus the following two that have net-Thus the following two that have net-
dipole moments are polar:dipole moments are polar:
– HH22OO
– NHNH33

27. Molecular structureMolecular structure
Molecular StructureMolecular Structure: or geometric structure refers to the: or geometric structure refers to the
three-dimensional arrangement of the atoms in athree-dimensional arrangement of the atoms in a
molecule.molecule.
Bond AngleBond Angle: The angle formed between two bonds in a: The angle formed between two bonds in a
molecule.molecule.

28. Molecular structure:Molecular structure:
VSEPRVSEPR
The VSEPR ModelThe VSEPR Model: The valence shell electron pair: The valence shell electron pair
repulsion model is useful for predicting the molecularrepulsion model is useful for predicting the molecular
structures of molecules formed from nonmetals.structures of molecules formed from nonmetals.
The structure around a given atom is determined byThe structure around a given atom is determined by
minimizing repulsions between electron pairs.minimizing repulsions between electron pairs.
The bonding and nonbonding electron pairs (lone pairs)The bonding and nonbonding electron pairs (lone pairs)
around a given atom are positioned as far apart asaround a given atom are positioned as far apart as
possible.possible.

29. Molecular Structure:Molecular Structure:
VSEPRVSEPR
Steps for Predicting Molecular Structure Using the VSEPRSteps for Predicting Molecular Structure Using the VSEPR
ModelModel
1. Draw the Lewis structure for the molecule.1. Draw the Lewis structure for the molecule.
2. Count the electron pairs and arrange them in the way2. Count the electron pairs and arrange them in the way
that minimizes repulsion (that is, put the lone pairs asthat minimizes repulsion (that is, put the lone pairs as
far apart as possible).far apart as possible).
3. Determine the positions of the atoms from the way the3. Determine the positions of the atoms from the way the
electron pairs are shared.electron pairs are shared.
4. Determine the name of the molecular structure from the4. Determine the name of the molecular structure from the
positions of the atoms.positions of the atoms.

31. ExampleExample
 BrBr22
 COCO22
 CFCF44
 PFPF33

32. Your turnYour turn
 NHNH44
++
 XeFXeF44
 AsIAsI55
 SFSF33
++
 II33
--