Ionic Bonding

Resonance Structures

VSEPR

Basic Shapes

3-D Notation

Hybridization (Lab)

Molecular Geometries

Octet Rule Polar Molecules

Lewis Structures Covalent Bonding

Types of Bonds

Chemical Bonding

• Chemical bond: attractive force holding two or more

atoms together.

• Covalent bond results from sharing electrons between

the atoms. Usually found between nonmetals.

• Ionic bond results from the transfer of electrons from a

metal to a nonmetal. Ionic compounds that form

electrolytes conduct electricity.

• Metallic bond: attractive force holding pure metals

together. Sea of electrons.

Chemical Bonds, Lewis Symbols, and the Octet Rule

Figure 8.3: Ionic Bonding

Figure 8.5: Covalent Bonding

Chemical Bonds

Bond Type Single Double Triple

# of e’s 2 4 6

Notation — =

Bond order 1 2 3

Bond

strengthIncreases from Single to Triple

Bond length Decreases from Single to Triple

Strengths of Covalent Bonds

Lewis Symbols

Chemical Bonds, Lewis Symbols, and the Octet Rule

The Octet Rule

• All noble gases except He has an s2p6 configuration.

• Octet rule: atoms tend to gain, lose, or share electrons

until they are surrounded by 8 valence electrons (4

electron pairs).

• Caution: there are many exceptions to the octet rule.

Chemical Bonds, Lewis Symbols, and the Octet Rule

Bond Polarity and Electronegativity

Electronegativity

• Electronegativity: The ability of one atoms in a

molecule to attract electrons to itself.

• Pauling set electronegativities on a scale from 0.7 (Cs) to

4.0 (F).

• Electronegativity increases

• across a period and

• down a group.

Figure 8.6: Electronegativities of Elements

Electronegativity

Bond Polarity and Electronegativity

Figure 8.7: Electronegativity and Bond Polarity

• There is no sharp distinction between bonding types.

• The positive end (or pole) in a polar bond is represented

+ and the negative pole -.

HyperChem

Drawing Lewis Structures

Follow Step by Step Method (See Ng Web-site)

1. Total all valence electrons. [Consider Charge]

2. Write symbols for the atoms and guess skeleton structure

[ define a central atom ].

3. Place a pair of electrons in each bond.

4. Complete octets of surrounding atoms. [ H = 2 only ]

5. Place leftover electrons in pairs on the central atom.

6. If there are not enough electrons to give the central atom

an octet, look for multiple bonds by transferring

electrons until each atom has eight electrons around it.

HyperChemCyberChem (Lewis) video

Lewis Structures – Examples - I

Lewis Structures – Examples - II

Exceptions to the Octet Rule

Central Atoms Having Less than an Octet

• Relatively rare.

• Molecules with less than an octet are typical for

compounds of Groups 1A, 2A, and 3A.

• Most typical example is BF3.

• Formal charges indicate that the Lewis structure with an

incomplete octet is more important than the ones with

double bonds.

Exceptions to the Octet Rule

Central Atoms Having More than an Octet

• This is the largest class of exceptions.

• Atoms from the 3rd period onwards can accommodate

more than an octet.

• Beyond the third period, the d-orbitals are low enough in

energy to participate in bonding and accept the extra

electron density.

HyperChem

• There are five fundamental geometries for molecular

shape:

Molecular Shapes: VSEPR

Molecular Shapes – 3D Notations

VSEPR (Ballons)-Movie Clip

Figure 9.3

HyperChem

Summary of VSEPR Molecular Shapes

e-pairs Notation Name of VSEPR shape Examples

2 AX2 Linear HgCl2 , ZnI2 , CS2 , CO2

3 AX3 Trigonal planar BF3 , GaI3

AX2E Non-linear (Bent) SO2 , SnCl2

4 AX4 Tetrahedral CCl4 , CH4 , BF4-

AX3E (Trigonal) Pyramidal NH3 , OH3-

AX2E2 Non-Linear (Bent) H2O , SeCl2

5 AX5 Trigonal bipyramidal PCl5 , PF5

AX4E Distorted tetrahedral

(see-sawed)

TeCl4 , SF4

AX3E2 T-Shaped ClF3 , BrF3

AX2E3 Linear I3- , ICl2

-

6 AX6 Octahedral SF6 , PF6-

AX5E Square Pyramidal IF5 , BrF5

AX4E2 Square Planar ICl4- , BrF4

-

See Ng Web-siteHyperChem CyberChm Gems

Examples: VSEPR Molecular Shapes - I

# electron

pairs on

Central

Atom A

Notation Example Lewis VSEPR & Name of Shape

2AX2

2 bp on A

3

AX3

3 bp on A

AX2E

2 bp and

1 lp on A

Examples: VSEPR Molecular Shapes – I – F08

Examples: VSEPR Molecular Shapes - II

# electron

pairs on

Central

Atom A

Notation Example Lewis VSEPR & Name of Shape

4

AX4

4 bp on A

AX3E

3 bp and

1 lp on A

AX2E2

2 bp and

2 lp on A

Examples: VSEPR Molecular Shapes – II – F08

Examples: VSEPR Molecular Shapes - III

# electron

pairs on

Central

Atom A

Notation Example LewisVSEPR & Name of

Shape

5

AX5

5 bp on A

AX4E

4 bp and 1

lp on A

AX3E2

3 bp and 2

lp on A

AX2E3

2 bp and 3

lp on A

Examples: VSEPR Molecular Shapes – III – F08

HyperChem

Examples: VSEPR Molecular Shapes - IV

# electron

pairs on

Central

Atom A

Notation Example Lewis VSEPR & Name of Shape

6

AX6

6 bp on A

AX5E

5 bp and

1 lp on A

AX4E2

4 bp and

2 lp on A

The Effect of Nonbonding Electrons

• By experiment, the H-X-H bond angle decreases on

moving from C to N to O:

• Since electrons in a bond are attracted by two nuclei, they do

not repel as much as lone pairs.

• Therefore, the bond angle decreases as the number of lone pairs

increases

VSEPR Model

104.5O107O

NHH

H

C

H

HHH109.5O

OHH

HyperChem

Figure 9.10: Shapes of Larger Molecules

• In acetic acid, CH3COOH, there are three central atoms.

VSEPR ModelHyperChem

Shapes of Larger Molecules

• In glycine (simplest amino acid), NH2CH2CO2H, there are four possible central atoms.

• Draw the Lewis Structure and the 3D VSEPR Molecular Geometry for glycine. Indicate the name of

the shape for all possible central atoms, including estimation of bond angles.

• Hint 1: Designate the 2nd carbon in the formula as the central atom in skeleton structure.

• Hint 2: The acid portion of glycine is the same as that of acetic acid.

Lewis-VSEPR HW assigned 10/29/10 . Due 11/1/10.

HyperChem

Solution Key

Figure 8.10: Drawing Lewis Structures

Resonance Structures

Figure 9.12

HyperChem

Figure 9.11: Molecular Shape and Molecular Polarity

HyperChem

Figure 9.13: Molecular Shape and Molecular Polarity

HyperChem

• Lewis structures and VSEPR do not explain why a bond

forms.

• How do we account for shape in terms of quantum

mechanics?

• What are the orbitals that are involved in bonding?

• We use Valence Bond Theory:

• Bonds form when orbitals on atoms overlap.

• There are two electrons of opposite spin in the orbital overlap.

Covalent Bonding and Orbital Overlap

Gems - Movie Clip

Figure 9.14: Covalent Bonding and Orbital Overlap

• To determine the electron pair geometry:

• draw the Lewis structure,

• count the total number of electron pairs around the central atom,

• arrange the electron pairs in one of the above geometries to

minimize e--e- repulsion, and count multiple bonds as one

bonding pair.

VSEPR Model (Figure 9.6)

VSEPR

Model

Drawing Lewis Structures

Formal Charge

• Consider:

• For C:

• There are 4 valence electrons (from periodic table).

• In the Lewis structure there are 2 nonbonding electrons and 3

from the triple bond. There are 5 electrons from the Lewis

structure.

• Formal charge: 4 - 5 = -1.

C N

Drawing Lewis Structures

Formal Charge

• Consider:

• For N:• There are 5 valence electrons.

• In the Lewis structure there are 2 nonbonding electrons and 3

from the triple bond. There are 5 electrons from the Lewis

structure.

• Formal charge = 5 - 5 = 0.

• We write:

C N

C NCyberChm Gems

Easy ways to remember shapes• Steric number- the number of atoms

bonded to the central atom of a molecule

plus the number of lone pairs on the central

atom. It is often used in VSEPR theory

(valence shell electron-pair repulsion

theory) in order to determine the particular

shape, or molecular geometry, that will be

formed.

Molecular Geometry Steps1. Memorize the structures in groups

according to steric number/ Bonding

number.

A. Steric number 2 = 1 structure

B. Steric number 3 = 2 structures

C. Steric number 4 = 3 structures

D. Steric number 5 = 4 structures

E. Steric number 6 = 3 structures.

Molecular Geometry Steps2. Now you have to memorize the structures in each

steric number group.

A. Steric number 2 = Linear (180 degrees)

B. Steric number 3 = Bent and Trigonal Planar (Both 120

degrees)

C. Steric number 4 = Tetrahedral, Trigonal Bipyramidal

and Bent again. (109.5, 107.3 and 104.5 degrees)

D. Steric number 5 = Trigonal Bipyramidal, See-Saw, T-

Shaped and Linear (Mixture of 90, 120 and 180

degrees)

E. Steric number 6 = Square Planar, Square Pyramid and

Octahedral (All 90 degrees) (Last one kind of breaks

the rule but I still find this helps. )

Molecular Geometry Steps3. Try to find a relationship between all the groups.

A. For groups 2 and 3, shapes pretty straightforward.

B. Group 4 are all tetrahedral shaped molecules (Think

group "4" / "Tetrahedral") with slight variations on the

bond angles based on the amount of lone pairs.

• Tetrahedral is the most uniform shape and it has a bond

angle closest to 120, with a slight repulsion from the

uppermost atom making a bond angle of 109.5.

• Trigonal Bipyramidal has a lone pair of electrons which

pushes the "side atoms" a little further away from 120

forming an angle of 107.3.

• Lastly, this variation of bent has two lone pairs of

electrons pushing the "side atoms" even further away

making an angle of 104.5.

Molecular Geometry Steps cont.C. Group 5, are the "weird shapes". This includes the

trigonal bipyramidal, see-saw, T-shape and linear. T

shape is 90 degrees because in the letter T, only 90

degree angles are present. Linear is 180 degrees. See-saw

has 3 angles, 1 angle along the top of the seat (180), 1

between the seats and the legs (90), and one between the

two legs (120). and trigonal Bipyramidal has 2 angles, 90

and 120 degrees.

D. Group 6 is the "square group" including: Square planar,

square pyramid and octahedral. (I know the last one isn’t

a square but, close enough). All squares consist of only

90 degree angles so these all only have 90 degree angles.

Using All of this info you can intuitively put together the

notation for each structure.

Ionic Bonding

Resonance Structures

VSEPR

Basic Shapes

3-D Notation

Hybridization (Lab)

Molecular Geometries

Octet Rule Polar Molecules

Lewis Structures Covalent Bonding

Types of Bonds

Chemical Bonding

Lewis

AXE notation

VSEPR shapes

Polarity