student ch 12 bonding short

8/7/2019 Student Ch 12 Bonding Short

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CHEMICALCHEMICALBONDINGBONDINGCHEMICALCHEMICALBONDINGBONDING

Cocaine

Chemistry IChemistry I Chapter 8Chapter 8

Chemistry I HonorsChemistry I Honors Chapter 12Chapter 12

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Chemical BondingChemical BondingProblems and questionsProblems and questions How is a molecule orpolyatomic ionHow is a molecule orpolyatomic ion

held together?held together?

Why are atoms distributed at strangeWhy are atoms distributed at strangeangles?angles?

Why are molecules not flat?Why are molecules not flat?

Can we predict the structure?Can we predict the structure?

How is structure related to chemicalHow is structure related to chemicaland physical properties?and physical properties?


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4The type of bond canThe type of bond can usuallyusually be calculated by findingbe calculated by findingthe difference in electronegativity of the two atoms thatthe difference in electronegativity of the two atoms that

are going together.are going together.


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5Electronegativity Difference

If the difference in electronegativitiesis between:

1.7 to 4.0: Ionic

0.3 to 1.7: Polar Covalent

0.0 to 0.3: Non-Polar Covalent

Example: NaCl

Na = 0.8, Cl = 3.0Difference is 2.2, so

this is an ionic bond!


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Ionic BondsIonic Bonds

Ionic BondsIonic BondsAll those ionic compounds were made fromAll those ionic compounds were made from

ionic bonds. Weve been through this inionic bonds. Weve been through this ingreat detail already. Positive cations andgreat detail already. Positive cations andthe negative anions are attracted to onethe negative anions are attracted to one

another(rememberthe Paula Abdulanother(rememberthe Paula AbdulPrinciple of Chemistry: Opposites Attract!)Principle of Chemistry: Opposites Attract!)

Therefore, ionicTherefore, ionic

compounds are usuallycompounds are usuallybetween metals andbetween metals andnonmetals (opposite endsnonmetals (opposite endsof the periodic table).of the periodic table).


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ElectronElectronDistribution inDistribution inMoleculesMolecules

ElectronElectronDistribution inDistribution inMoleculesMolecules

Electron distribution isElectron distribution is

depicted withdepicted with LewisLewis(electron dot)(electron dot)structuresstructures

This is how youThis is how youdecide how manydecide how manyatoms will bondatoms will bondcovalently!covalently!

(In ionic bonds, it(In ionic bonds, itwas decided withwas decided withcharges)charges)

G. N. LewisG. N. Lewis

18751875 -- 19461946


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Bond and Lone PairsBond and Lone PairsBond and Lone PairsBond and Lone Pairs Valence electrons are distributedValence electrons are distributed

as shared oras shared orBOND PAIRSBOND PAIRS andandunshared orunshared orLONE PAIRS.LONE PAIRS.

H Cllone pair (LP)

shared or

bond pair

This is called aThis is called a LEWISLEWIS

structure.structure.


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Bond FormationBond FormationBond FormationBond Formation

A bond can result from anA bond can result from an overlapoverlap ofofatomic orbitals on neighboring atoms.atomic orbitals on neighboring atoms.

ClH H Cl

+

Overlap of H (1s) and Cl (2p)

Note that each atom has a single,Note that each atom has a single,

unpaired electron.unpaired electron.


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Review of Valence ElectronsReview of Valence ElectronsReview of Valence ElectronsReview of Valence Electrons

Rememberfrom the electron chapterthatRememberfrom the electron chapterthatvalence electrons are the electrons in thevalence electrons are the electrons in theOUTERMOST energy level thats why we didOUTERMOST energy level thats why we didall those electron configurations!all those electron configurations!

B isB is 1s1s22 2s2s22 2p2p11; so the outerenergy level is 2,; so the outerenergy level is 2,and there are 2+1 = 3 electrons in level 2.and there are 2+1 = 3 electrons in level 2.These are the valence electrons!These are the valence electrons!

Br isBr is [Ar] 4s[Ar] 4s22 3d3d1010 4p4p55

How many valence electrons areHow many valence electrons are

present?present?


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12Steps for Building a Dot StructureSteps for Building a Dot StructureSteps for Building a Dot StructureSteps for Building a Dot Structure

Ammonia, NHAmmonia, NH331. Decide on the central atom; neverH.1. Decide on the central atom; neverH.Why?Why?

If there is a choice, the central atom is atom of lowest affinityIf there is a choice, the central atom is atom of lowest affinityforelectrons.forelectrons.(Most of the time, this is the(Most of the time, this is the least electronegative atomleast electronegative atomininadvanced chemistry we use a thing called formal charge to determine theadvanced chemistry we use a thing called formal charge to determine the

central atom. But thats anotherstory!)central atom. But thats anotherstory!)Therefore, N is central on this oneTherefore, N is central on this one

2. Add up the numberof valence electrons that can be2. Add up the numberof valence electrons that can beused.used.

H = 1 and N = 5H = 1 and N = 5

Total = (3 x 1) + 5Total = (3 x 1) + 5

= 8 electrons / 4 pairs= 8 electrons / 4 pairs


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3.3. Form a single bond between theForm a single bond between thecentral atom and each surroundingcentral atom and each surroundingatom (each bond takes 2 electrons!)atom (each bond takes 2 electrons!)

H H

H

N

Building a Dot StructureBuilding a Dot Structure

H

H

H

N

4.4. Remaining electrons form LONERemaining electrons form LONE

PAIRS to complete the octet as needed (orPAIRS to complete the octet as needed (or

duet in the case of H).duet in the case of H).

3 BOND PAIRS and 1 LONEPAIR.3 BOND PAIRS and 1 LONEPAIR.

Note that N has a share in 4 pairs (8 electrons), whileNote that N has a share in 4 pairs (8 electrons), while

H shares 1 pair.H shares 1 pair.


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5.5. Check to make sure there are 8 electronsCheck to make sure there are 8 electronsaround each atom except H. H shouldaround each atom except H. H shouldonly have 2 electrons. This includesonly have 2 electrons. This includesSHARED pairs.SHARED pairs.

Building a Dot StructureBuilding a Dot Structure

6.6.Also, check the number of electrons in yourAlso, check the number of electrons in your

drawing with the number of electrons fromdrawing with the number of electrons from

step 2. If you have more electrons in thestep 2. If you have more electrons in the

drawing than in step 2, you must makedrawing than in step 2, you must make

double or triple bonds. If you have lessdouble or triple bonds. If you have less

electrons in the drawing than in step 2, youelectrons in the drawing than in step 2, you

made a mistake!made a mistake!

H

H

H

N


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Carbon Dioxide, COCarbon Dioxide, CO22Carbon Dioxide, COCarbon Dioxide, CO22

1. Central atom =1. Central atom =

2. Valence electrons =2. Valence electrons =

3. Form bonds.3. Form bonds.

O OC

4. Place lone pairs on outeratoms.4. Place lone pairs on outeratoms.

This leaves 12 electrons (6 pair).This leaves 12 electrons (6 pair).

5. Check to see that all atoms have 8 electrons5. Check to see that all atoms have 8 electrons

around it except for H, which can have 2.around it except for H, which can have 2.

C 4 eC 4 e--

O 6 eO 6 e-- X 2 Os = 12 eX 2 Os = 12 e--

Total: 16 valence electronsTotal: 16 valence electrons


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Carbon Dioxide, COCarbon Dioxide, CO22Carbon Dioxide, COCarbon Dioxide, CO22

O OC

O OC

O OC

O OC

6. There are too many electrons in ourdrawing. We must form6. There are too many electrons in ourdrawing. We must form

DOUBLEBONDS between C and O. Instead of sharing only 1 pair,DOUBLEBONDS between C and O. Instead of sharing only 1 pair,

a double bond shares 2 pairs. So one pair is taken away froma double bond shares 2 pairs. So one pair is taken away from

each atom and replaced with anotherbond.each atom and replaced with anotherbond.

C 4 eC 4 e--

O 6 eO 6 e-- X 2 Os = 12 eX 2 Os = 12 e--

Total: 16 valence electronsTotal: 16 valence electrons

How many are in the drawing?How many are in the drawing?


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Double and evenDouble and even

triple bonds aretriple bonds arecommonlycommonlyobserved forC, N,observed forC, N,

P, O, and SP, O, and S

O OC

O OC

HH22COCO

SOSO33

CC22FF44


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Violations of the Octet RuleViolations of the Octet Rule(Honors only)(Honors only)

Violations of the Octet RuleViolations of the Octet Rule(Honors only)(Honors only)

Usually occurs with B and elementsUsually occurs with B and elementsof higher periods. Commonof higher periods. Commonexceptions are: Be, B, P, S, and Xe.exceptions are: Be, B, P, S, and Xe.

BF3BF3

SF4SF4

Be: 4Be: 4

B: 6B: 6

P: 8 OR 10P: 8 OR 10

S: 8, 10, OR 12S: 8, 10, OR 12

Xe: 8, 10, OR 12Xe: 8, 10, OR 12


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MOLECULARMOLECULAR

GEOMETRYGEOMETRY

MOLECULARMOLECULAR

GEOMETRYGEOMETRY


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VSEPRVSEPR

VValencealence SShellhell EElectronlectron PPairairRRepulsionepulsiontheory.theory.

Most important factor inMost important factor indetermining geometry is relativedetermining geometry is relativerepulsion between elect

ron pai

rs.r

epulsion between electron pai

rs.

Molecule adoptsMolecule adopts

the shape thatthe shape that

minimizes theminimizes the

electron pairelectron pairrepulsions.repulsions.

Molecule adoptsMolecule adopts

the shape thatthe shape that

minimizes theminimizes the

electron pairelectron pairrepulsions.repulsions.

MOLECULAR GEOMETRYMOLECULAR GEOMETRYMOLECULAR GEOMETRYMOLECULAR GEOMETRY


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Some Common GeometriesSome Common Geometries

LinearLinear

Trigonal PlanarTrigonal Planar TetrahedralTetrahedral


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23VSEPR chartsVSEPR charts

Use the Lewis structure to determine theUse the Lewis structure to determine thegeometry of the moleculegeometry of the molecule

Electron arrangement establishes the bondElectron arrangement establishes the bondanglesangles

Molecule takes the shape of that portion ofMolecule takes the shape of that portion ofthe electron arrangementthe electron arrangement

Charts look at the CENTRAL atom for all data!Charts look at the CENTRAL atom for all data!

Think REGIONS OF ELECTRON DENSITYThink REGIONS OF ELECTRON DENSITYrather than bonds (for instance, a doublerather than bonds (for instance, a doublebond would only be 1 region)bond would only be 1 region)


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Other VSEPR chartsOther VSEPR charts


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Structure Determination by VSEPRStructure Determination by VSEPRStructure Determination by VSEPRStructure Determination by VSEPR

Water, HWater, H22OOThe electron pairThe electron pair

geometry isgeometry isTETRAHEDRALTETRAHEDRAL

The electron pairThe electron pair

geometry isgeometry isTETRAHEDRALTETRAHEDRAL

The molecularThe molecular

geometry isgeometry is

BENTBENT..

The molecularThe molecular

geometry isgeometry is

BENTBENT..

H O H

H O H

2 bond2 bond

pairspairs2 lone2 lone

pairspairs


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Structure Determination byStructure Determination byVSEPRVSEPR

Structure Determination byStructure Determination byVSEPRVSEPR

Ammonia, NHAmmonia, NH33

The electron pairgeometry is tetrahedral.The electron pairgeometry is tetrahedral.

H

H

H

lone pair of electronsin tetrahedral position

N

TheThe MOLECULAR GEOMETRYMOLECULAR GEOMETRY the positions of thethe positions of the

atomsatoms isis TRIGONALTRIGONAL PYRAMIDPYRAMID..

TheThe MOLECULAR GEOMETRYMOLECULAR GEOMETRY the positions of thethe positions of the

atomsatoms isis TRIGONALTRIGONAL PYRAMIDPYRAMID..


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Bond PolarityBond PolarityBond PolarityBond PolarityHCl isHCl is POLARPOLAR because it has abecause it has a

positive end and a negativepositive end and a negativeend. (difference inend. (difference inelectronegativity)electronegativity)

Cl has a greater share inCl has a greater share in

bonding electrons thanbonding electrons than

does H.does H.

Cl has a greater share inCl has a greater share in

bonding electrons thanbonding electrons than

does H.does H.

Cl has slight negative chargeCl has slight negative charge ((--HH)) and H hasand H has

slight positive chargeslight positive charge (+(+ HH))

H Cl

+H -H

H Cl

+H -H


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Diatomic ElementsDiatomic Elements

These elements do not exist as a single atom;they always appear as pairs

When atoms turn into ions, this NO LONGERHAPPENS! Hydrogen

Nitrogen

Oxygen

Fluorine

Chlorine Bromine

Iodine

Remember:Remember:

BrINClHOFBrINClHOF

student ch 12 bonding short

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