Unit 6: Chemical Bonding Refer to Ch. 8 & 9 for supplemental reading.

Unit 6: Chemical BondingUnit 6: Chemical Bonding

Refer to Ch. 8 & 9 for Refer to Ch. 8 & 9 for supplemental reading.supplemental reading.

1. Chemical Bond:1. Chemical Bond: an attractive force that an attractive force that holds 2 atoms togetherholds 2 atoms together

3 types: 3 types: ionic, covalent, metallicionic, covalent, metallic

Valence ElectronsValence Electrons

The electrons in the The electrons in the outerouter energy level of energy level of an atom. an atom.

They are like the front They are like the front lines of an army. lines of an army. They are the electrons They are the electrons involved in involved in bondingbonding..

ReviewReviewHow do you find valence electrons?How do you find valence electrons?

Hint there are Hint there are twotwo ways! ways!Examples: Look at the group # for the Examples: Look at the group # for the

representative elements.representative elements.Mg ___Mg ___O ___O ___Ar ___Ar ___Si ___Si ___

Examples: Write the electron configuration.Examples: Write the electron configuration.MgMgOO

2

6

8

4

1s1s22 2s 2s22 2p 2p66 3s3s2

1s1s22 2s 2s2 2p 2p4

Electron Dot StructuresElectron Dot Structures

Depicts element symbol w/ valence eDepicts element symbol w/ valence e-- shown as dots.shown as dots.

Na Mg Al

Cl Ar

Si

ON

Ionic BondsIonic Bonds

Occurs when Occurs when ionsions of opposite charge (+,-) of opposite charge (+,-) attractattract each other. each other.Metal ion – Nonmetal ionMetal ion – Nonmetal ion

Simplest attractionSimplest attraction NaCl MgFNaCl MgF22

Polyatomic ions: Molecules that are charged.Polyatomic ions: Molecules that are charged.Al(POAl(PO44) (NH (NH44))22(SO(SO44))

POPO44 is phosphate with a -3 charge is phosphate with a -3 charge

SOSO44 is sulfate with a -2 charge is sulfate with a -2 charge

Formation of Ionic BondFormation of Ionic BondCation- positive ion (+) Cation- positive ion (+) (Cats (Cats

have paws)have paws)Forms when a Forms when a metalmetal atom atom

losesloses e e-- to become stable. to become stable.Anion- negative ion (-) Anion- negative ion (-) ((AA

NNegative egative IonIon))Forms when a Forms when a nonmetalnonmetal atom atom

gains egains e-- to become stable to become stableAn ionic bond is formed when An ionic bond is formed when

ee-- are are transferredtransferred between between atoms and the resulting ions atoms and the resulting ions stick together.stick together.

ExamplesExamplesFormation of NaClFormation of NaCl

Na Cl Na Cl → [Na]→ [Na]++ [ Cl ] [ Cl ]-- = NaCl = NaCl

Formation of MgFFormation of MgF22

MgMg F F F F [Mg] [Mg]2+2+ [ F ] [ F ]-- [ F ] [ F ]-- = = MgFMgF22

How would a compound form between two aluminum and How would a compound form between two aluminum and three oxygen? three oxygen?

Electron Configuration of IonsElectron Configuration of Ions

Cation exampleCation example: (metal): (metal)Ca atom:Ca atom: 1s1s22 2s 2s22 2p 2p66 3s 3s22 3p 3p66 4s 4s22

CaCa2+2+ ion: ion: 1s1s22 2s 2s22 2p 2p66 3s3s22 3p 3p66 Lost 2 Lost 2 electronselectrons to obtain noble gas to obtain noble gas configuration (octet)configuration (octet)

Electron Configuration of IonsElectron Configuration of Ions

Anion exampleAnion example: (nonmetal): (nonmetal)N atom:N atom: 1s1s22 2s 2s22 2p 2p33

NN3-3- ion: ion: 1s1s22 2s 2s22 2p 2p66

GainedGained 3 electrons3 electrons to obtain noble gas to obtain noble gas configuration (octet) configuration (octet)

Properties of Ionic CompoundsProperties of Ionic CompoundsIONIC

Bond Formation

Type of Structure

Boiling Point

Electrical Conductivity

OtherProperties

high

yes* (solution or liquid)

high

MeltingPoint

Crystal lattice

Physical State Solid (hard and rigid)

Hard, rigid and brittle

e- transferred from metal to nonmetal

The force that holds ionic compounds is really strong.

So you see all of these characteristics.

ElectrolyteElectrolyteA substance that conducts electricityA substance that conducts electricity

Because of ionic bonds ionic (charged) Because of ionic bonds ionic (charged) nature, ionic compounds conduct electricity in nature, ionic compounds conduct electricity in the molten or aqueous (dissolved in water) the molten or aqueous (dissolved in water) forms.forms.

Covalent BondsCovalent Bonds Occurs when 2 Occurs when 2

nonmetalsnonmetals shareshare pairs of pairs of electrons to become electrons to become stable. These are called stable. These are called molecular compounds.molecular compounds.

Examples:Examples: HH22OO COCO22

CC66HH1212OO66 PClPCl55

Notice all of these Notice all of these elements in the molecule elements in the molecule are nonmetals!are nonmetals!

Covalent BondsCovalent Bonds

Covalent bonds can be Covalent bonds can be singlesingle (1 shared pair) (1 shared pair)doubledouble (2 shared pairs) (2 shared pairs)or or tripletriple (3 shared pairs) (3 shared pairs)

Bond strength: triple > Bond strength: triple > double > singledouble > single

Bond length: single > Bond length: single > double > triple double > triple

Creating Lewis StructuresCreating Lewis Structures

Follow this system:Follow this system:Example: HExample: H22OO1) Draw a “skeleton” of the molecule. It 1) Draw a “skeleton” of the molecule. It

generally works to place the “different” generally works to place the “different” atom in the center. atom in the center.

H O HH O H

Creating Lewis StructuresCreating Lewis Structures

Find the needed electrons (Find the needed electrons (NN) for ) for eacheach atom and add them up. atom and add them up. NN will be 8 for will be 8 for most elements, with these exceptions: most elements, with these exceptions:

H gets 2 valence eH gets 2 valence e--

Be gets 4 valence eBe gets 4 valence e--

B gets 6 valence eB gets 6 valence e--

•N = 12

•H = 2

•O = 8

•H = 2

2

4 8 8 8 8

8

6

8

NEED

3) Find the available (valence) electrons 3) Find the available (valence) electrons (A) for (A) for eacheach atom and then add them up*. atom and then add them up*.

A = A =

*special note: when completing a Lewis structure for a *special note: when completing a Lewis structure for a polyatomic ion, you will need to correct A by adding the polyatomic ion, you will need to correct A by adding the absolute value of the charge if negative, and subtracting absolute value of the charge if negative, and subtracting the charge if positive. For example, for the ion POthe charge if positive. For example, for the ion PO44

3-3-, ,

you would you would addadd 3 to A. For the ion NH 3 to A. For the ion NH4+4+, you would , you would subtractsubtract 1 from A. (You do the opposite of the charge.) 1 from A. (You do the opposite of the charge.)

H = 1

O = 6

H = 1

Total A = 8

N = 12

A = 8

1

2 4 5 6 7

8

3

Figure out through e config

Available

4) Find the shared (S) electrons for the 4) Find the shared (S) electrons for the entire molecule by this formula: S = N – Aentire molecule by this formula: S = N – A

S = S = S= 12 – 8 = 4

N = 12

A = 8

S = 4

5) The shared electrons are the bonding 5) The shared electrons are the bonding electrons. Place all of the shared electrons electrons. Place all of the shared electrons between the atoms.between the atoms.

H O HH O H 6) You 6) You mustmust place place all all of the available (A) of the available (A)

electrons in the picture. The shared electrons are electrons in the picture. The shared electrons are part of the available. See how many of the part of the available. See how many of the available electrons still need to be placed, and available electrons still need to be placed, and put them in the picture as put them in the picture as lone pairslone pairs (unshared (unshared pairs) so that every atom gets an pairs) so that every atom gets an octetoctet (remember H only needs 2). (remember H only needs 2).

H O HH O H

N = 12

A = 8

S = 4

N = 12

A = 8

S = 44

CFCF44

N=N=

A=A=

S=S=

FF C F

F

8+(4x8) = 40

4+(4x7) = 32

8 24

BeClBeCl22

N=N=

A=A=

S=S=

4+(2x8) = 20

2+(2x7) = 16

4 12

Cl Be Cl

COCO22

N=N=

A=A=

S=S=

8+(2x8) = 24

4+(2x6) = 16

8 8 O C O

Polyatomic IonsPolyatomic Ions

To find total # of valence eTo find total # of valence e- - (A):(A):Add 1eAdd 1e-- for each negative charge. for each negative charge.Subtract 1eSubtract 1e-- for each positive charge. for each positive charge.

Place brackets around the ion and label the Place brackets around the ion and label the charge.charge.

Polyatomic IonsPolyatomic Ions

ClOClO44--

OO Cl O

O

N=N=

A=A=

S=S=

8+(4x8) = 40

7+(4x6) = 31

24

+1 =32

8

NonpolarNonpolar

PolarPolar

IonicIonic

View Bonding Atomic Bonding : Chemistry ZoneAnimations.

Bond PolarityBond Polarity


Most bonds are Most bonds are a blend of ionic a blend of ionic and covalent and covalent characteristics.characteristics.

Difference in Difference in electronegativity electronegativity determines bond determines bond type. (subtract)type. (subtract)

If EN is: Bond type is:

< 0.4 Nonpolar covalent

EN < 1.7

Polar covalent

> 1.7 Ionic

Nonpolar Covalent BondNonpolar Covalent Bondee-- are shared equally between the atoms are shared equally between the atomssymmetrical esymmetrical e-- density densityusually occurs between identical atoms usually occurs between identical atoms


Bond PolarityBond PolarityPolar Covalent BondPolar Covalent Bond

ee-- are shared unequally are shared unequallyOne atom “hogs” the electronsOne atom “hogs” the electrons

asymmetrical easymmetrical e-- density density results in partial charges (dipole) results in partial charges (dipole)

O is more electronegative than H and pulls the electrons closer to itself.

Electronegativity ChartElectronegativity Chart

If ΔEN is: Bond type is:


0.4 < Δ EN < 1.7 Polar covalent

> 1.7 Ionic

Use the Electronegativity Chart to determine if the bond between atoms is nonpolar covalent, polar covalent, or ionic.

Larger EN minus the smaller EN

If ΔEN is: Bond type is:


0.4 < Δ EN < 1.7 Polar covalent

> 1.7 Ionic

Examples:Examples:

ClCl22

HClHCl

NaClNaCl

3.16-3.16=0.03.16-3.16=0.0NonpolarNonpolar

3.16-2.2=0.963.16-2.2=0.96PolarPolar

3.16-..93=2.233.16-..93=2.23IonicIonic

Metallic BondMetallic Bond

Bond between Bond between metalmetal and and metalmetal..An “electron sea” is created where An “electron sea” is created where

electrons overlap into neighboring atoms.electrons overlap into neighboring atoms.The electrons move around.The electrons move around.

Metallic BondMetallic Bond

Because the electrons are free to move Because the electrons are free to move around from atom to atom, we see the around from atom to atom, we see the properties that we know of metals.properties that we know of metals.

http://www.pbs.org/wgbh/nova/tech/structure-of-metal.html

Click on this for a cool interactive on metal properties.

Metal PropertiesMetal Properties

Malleable and ductile:Malleable and ductile: the electrons can the electrons can move past each other so the shape can move past each other so the shape can change.change.

Free flowing electrons can Free flowing electrons can conductconduct heat heat and electricity quickly to other atoms.and electricity quickly to other atoms.

VSEPR TheoryVSEPR Theory VValence alence SShell hell EElectron lectron PPair air RRepulsion epulsion TTheoryheory

Electron pairs place themselves so that they Electron pairs place themselves so that they are as far apart from each other as possible.are as far apart from each other as possible.

A. VSEPR TheoryA. VSEPR Theory

Types of eTypes of e-- Pairs PairsBonding pairsBonding pairs - form bonds between the - form bonds between the

atomsatomsLone pairsLone pairs - nonbonding e - nonbonding e- - (electrons that (electrons that

are not between atoms)are not between atoms)

Lone pairs repel

more strongly than

bonding pairs!!!

A. VSEPR TheoryA. VSEPR TheoryLone pairs reduce the bond angle Lone pairs reduce the bond angle

between atoms.between atoms.

VS

Draw the Lewis Diagram.Draw the Lewis Diagram.Tally up eTally up e-- pairs on central atom. pairs on central atom.

double/triple bonds = ONE pairdouble/triple bonds = ONE pair

Shape is determined by the # of Shape is determined by the # of bonding pairs and lone pairs.bonding pairs and lone pairs.

B. Determining Molecular B. Determining Molecular ShapeShape

Common Molecular ShapesCommon Molecular Shapes

2 bonding 2 bonding pairspairs

0 lone pairs0 lone pairs

LINEARLINEARBeHBeH22


2 bonding 2 bonding pairs pairs

1 lone pair1 lone pair

BENTBENT

120°120°

SOSO22

2 bonding pairs2 bonding pairs


BENTBENT

109.5°109.5°

HH22OO




TRIGONAL PLANARTRIGONAL PLANAR



1 lone pair1 lone pair

PYRAMIDALPYRAMIDALNHNH33




TETRAHEDRALTETRAHEDRALCHCH44


PFPF33

3 bond3 bond

1 lone1 lone

PYRAMIDALPYRAMIDAL

F P FF

ExamplesExamples

COCO22

O C O2 total2 total

2 bond2 bond

0 lone0 lone LINEARLINEAR

180°180°

ExamplesExamples

ExamplesExamples

HH22SS CClCCl44

BFBF33 SiOSiO22

Unit 6: Chemical Bonding Refer to Ch. 8 & 9 for supplemental reading.

Documents

valence en

available valence electrons

valence eb

1s2 2s2 2p3n3 ion

nonmetal atom gains

metalca atom

nonmetaln atom

different atom