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CH 1: Structure and Bonding

Renee Y. Becker

CHM 2210

Valencia Community College

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Organic Chemistry (present definition): – the chemistry of carbon compounds

Organic Chemistry (Historical definition): – Study of compounds extracted from living organisms,

study of compounds having the vital force

Vitalism: – The belief that natural products needed a “vital force” to

create them– In the 19th century experiments showed that organic

compounds could be synthesized from inorganic compounds

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Friedrich Wohler

• In 1828, Wohler synthesized urea from ammonium cyanate

heatNH4

+ OCN

- H2N C NH2

O

ureaAmmonium cyanate (inorganic)

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Natural Product or Synthesized

• Plant-derived compounds and synthesized compounds are identical (almost)

– You can tell them apart by 14C dating

– Synthesized compounds have a lower content of radioactive 14C, their 14C has decayed over time

– BUT, plant-derived compounds are recently synthesized from CO2 in the air and therefore have a higher content of radioactive 14C

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• Not all carbon compounds are organic

– Diamonds, graphite, CO2, NH4+ -OCN, Na2CO3

• Derived from minerals and have inorganic properties

– Most of the millions of carbon compounds are classified as organic

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Structure of the Atom

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Atomic Orbitals

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• Aufbau principle: Place electrons in lowest energy orbital first.

• Hund’s rule: Equal energy orbitals are half-filled, then filled.

Electronic Configurations

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1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d 7s 7p

Increasing Energy

[He][Ne] [Ar] [Kr] [Xe] [Rn]

Core

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Example 1: Electron Configuration

Draw electron configuration

1. Cl

2. Cl-

3. Mg

4. Mg2+

5. Fe3+

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• Ionic bonding: electrons are transferred.

• Covalent bonding: electron pair is shared.

Bond Formation

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Lewis Structures

• Bonding electrons

• Nonbonding electrons or lone pairs

Satisfy the octet rule!

C

H

H

H

OH

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Multiple Bonding

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Example 2: Lewis Dot Structures

Draw Lewis structures for the following

a) NH3

b) CH3CH2F

c) CH3OCH3

d) BF3

e) C3H4

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Calculating Formal Charge

C

H

H

H

C

O

O P

O

OO

O

3-

Formal charge =

(# own valence electrons in free atom)-(# own valence electrons in bonded atom)

Put in formal charges

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Ionic Structures

C

H

H

H N

H

H

H

+

Cl-

Na O CH3 or O CH3Na+

_X

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Example 3: Lewis Dot Structures

Draw the Lewis structure for the following compounds or ions, showing formal charges

a) (CH3)+

b) (CH3)-

c) NH4Cl

d) H3O+

e) (CH3)2NH2Cl

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Valence Bond Theory

1. Covalent bonds are formed by overlapping of atomic orbitals, each of which contains one electron of opposite spin.

2. Each of the bonded atoms maintains its own atomic orbitals, but the electron pair in the overlapping orbitals is shared by both atoms.

3. The greater the amount of orbital overlap, the stronger the bond.

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Valence Bond Theory

• Linus Pauling: Wave functions from s orbitals & p orbitals could be combined to form hybrid atomic orbitals.

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• sp hybrid: acetylene HH

Bond angle 180Electron pair Geometry linear

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• sp2 hybrid: EthyleneH

H

H

H

Bond angle 120 (varies)Electron pair Geometry Trigonal Planar

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• sp2 hybrid (π bond):

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• sp3 hybrid: Ethane H

H

H

H

H

H

Bond angle 109.5 (varies)Electron pair Geometry Tetrahedral

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sp3d hybrid:

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• sp3d2 hybrid:

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Example 4: Hybridization

What is the hybridization of the non-hydrogen atoms?

H

HH

H

H

H

H

H

OH

HH

H

HH

HH

O

OHH

HH

H

H

HH

1.

2.

3.

4.

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Molecular Orbital Theory

• The molecular orbital (MO) model provides a better explanation of chemical and physical properties than the valence bond (VB) model.

– Atomic Orbital: Probability of finding the electron within a given region of space in an atom.

– Molecular Orbital: Probability of finding the electron within a given region of space in a molecule.

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Molecular Orbital Theory

• Additive combination of orbitals () is lower in energy than two isolated 1s orbitals and is called a bonding molecular orbital.

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Molecular Orbital Theory

• Subtractive combination of orbitals () is higher in energy than two isolated 1s orbitals and is called an antibonding molecular orbital.

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Molecular Orbital Theory

• Molecular Orbital Diagram for H2:

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Molecular Orbital Theory

• Molecular Orbital Diagrams for H2– and

He2:

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Chemical Formulas

Full structural formula (no lone pairs shown)

Line-angle formula

Skeletal

Condensed structural formula

Molecular formula

Empirical formula

CH3COOH

C2H4O2

CH2O

C

H

H

H

C

O

O H

OH

O

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Example 5: Chemical Formulas

Draw the condensed structural formula for the following

OH

O1. 2.

3. 4.

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Example 6: Chemical Formulas

Draw the skeletal structure

1. CH3(CH2)4CH3

2. CH3CH(CH3)2

3. CH3CH(CH3)CH(CH2CH3)CH2CH3

4. C(CH3)4