Introduction&

Atomic Structure, Molecular Structure and Bonding

Organic Chemistry: IntroductionWhat Is Chemistry? Chemistry Is The Study Of Matter & The Changes It Undergoes

Two Main “Branches” of Chemistry

Organic Chemistry

Inorganic Chemistry

• Term Coined by Berzelius ~ 1807

• Matter Derived From Living Things

• Study of Carbon Compounds (C,H,N,O)

• Matter Derived From Nonliving Things

• Vast Majority of the Periodic Table

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Influence of Organic Chemistry

Organic Chemistry Is Important to Medicine: Ancient and Modern

• Plant Extracts as Medicines…Active Ingredients are Organic Compounds

• Prescription Drugs….Prepared by “Synthetic Chemists”

Organic Chemistry and Dyes:

• 1st Solid Link of Industry and Research

• $$ Derived From Research

Organic Chemistry and Materials Development:

• Synthetic Fibers….Nylon

• Synthetic Rubber….Neoprene

• Chemistry of Polymers (Plastics)

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Organic Chemistry and You?

Redox ReactionsAlcoholsAldehydesKetones Alkanes/alkenes

EthersCarboxylic acids

ConcentrationRedox ReactionsSpectrometry

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In this unit, we will review…

1. Atomic Structure2. Lewis Dot Structures and Formal Charge3. Ionic and Covalent Bonds4. Electronegativity and Polarity5. Molecular Geometry6. Multiple Bonds

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Modern Atomic Theory

Atoms have an internal structure consisting of one or more subatomic particles:

proton positive chargemass = 1.673 x 10-27 kg

neutron no chargemass = 1.675 x 10-27 kg

electron negative chargemass = 9.109 x 10-31 kg

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Most of the mass of an atom is concentrated in the nucleus, which contains one or more positively charged protons and neutrons with no electrical charge.

proton

neutron

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One or more negatively charged electrons are in constant motion outside the nucleus.

What is the overall electrical charge if the number of electrons equals the number of protons?

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Valence and Core Electrons

Electrons contained in the outermost shell are called ________electrons.

All other electrons are called ______ electrons.

e-

e-

e-e-

e-

How many valence electrons does this atom have? Core electrons? Which number matters more?

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How many valence electrons (ve-’s) does carbon have? Calcium? What element is depicted in the image on the right?

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Chemical Bonding

Chemical bonds are the forces that hold atoms together in compounds. We use Lewis Dot structures to represent these atoms and compounds.

C O OC

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Drawing Lewis Dot Structures

1. Count total ve-’s available2. Draw a Lewis sketch

– H is never central; C is often central3. Draw in electrons to fulfill octet and duet rules

– C “likes” 8 electrons; H “likes” 2 electrons4. Count ve-’s and compare to #25. If too many e-’s, make a double bond6. Calculate formal charge (FC) to double check structure

– No or low FCs (e.g. +1) more likely than large FCs (e.g. +2)

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Example

NH3

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Formal Charge

Formal charge = ve-’s – (lone pairs + bonds)

In a neutral molecule, the sum of the FCs = zero. For an ion, the sum of the FCs = the charge of the ion.

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Formal Charge –the easy way!1. Circle the atom of interest.2. Count the electrons inside the circle. If the circle

“breaks” a bond, only count one electron of the bond.3. Take the ve-’s for the atom (its group number) and

subtract #2.

O OCFC of oxygen= 6 – (6) = 0

FC of carbon= 4 – (4) = 0

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Resonance StructuresResonance structures result when more than

one valid Lewis dot structure can be drawn for one molecule. – The positions of the nuclei can’t change (C, H, etc.)– The positions of multiple bonds or lone pairs can

move– Low FCs are still favored

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CH O

O

CH O

O

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Computing Formal Charges“Normal” covalent bonding patterns:

C

C

C

C

Carbon Nitrogen

N

N

N

Oxygen

O

O

Halogens

X

Four bondsNo lone pairs

Three bondsOne lone pair

Two bondsTwo lone pairs

One bondThree lone pairs

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Computing Formal ChargesCommon structures with formal charges:

C

C

Carbon Nitrogen

N

N

N

Oxygen

O

O

Halogens

X

N

N

N

O

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Ionic versus CovalentBonds formed by the transfer of electrons from one atom to

another are __________.

Example:Sodium chloride (NaCl)

Na Na+ + e-

Cl + e- Cl- __Na + Cl NaCl

+ + + +

+ + + +

+ + + +

_ _ _

_ _ _

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Bonds formed by the sharing of electrons between two atoms are __________.

Example:Glucose (C6H12O6)

CH

O

CH2OH

H

OH

H

H

OH

H

OH

OH

CHO

OHH

HHO

OHH

OHH

CH2OH

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Polar Covalent Bonds

Polar bonds are bonds between atoms created by sharing electrons unevenly.

H F

F F

Uneven sharing is the result of electron “greedy” atoms (i.e. more electronegative atoms).

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ElectronegativityElectronegativity is a measure of the tendency of an

atom to attract a bonding pair of electrons.

Electronegativity differences result in polar covalent bonds.

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Polar Covalent MoleculesA polar molecule is a molecule that is electrically

asymmetrical, resulting in charges at two points. The molecule is said to have a molecular dipole or dipole moment.

H Cl OH H

O

CH3C CH3

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Polar Covalent Molecules

Not all molecules that contain polar bonds will be polar molecules!

O C O

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Molecular GeometryCommon geometries:

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C

C

C

O

H

HHHH

H

Acetone C3H6O

Is acetone ionic or covalent?What its geometry?

PQ

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Atomic orbitals (AOs)are the probability distribution about one atomic nucleus(found using wave functions ψ)

AOs relate to quantum numbers (n, l, ml, ms)

Each AO can have, at most, two e- (Pauli Exclusion Principle)

AOs are filled with e-’s from the lowest energy to the highest (Aufbau Principle)

The electron configuration with the highest number of unpaired spin is more stable (Hund’s rule)

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AtomElectronicStructure

ElectronicConfiguration

Lewis DotStructure

Boron

Phosphorus

1s22s22p1

[Ne] 3s23p3

3p

3s

2p

2s

1s

3p

3s

2p

2s

1s

B

P

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Scandium5

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CarbonAtomic Number = 6

2p

2s

1s

Atomic Number = 6

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Hybridized Orbitals5

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Hybridized OrbitalsWhen carbon double bonds, the 2s, 2px and 2py orbitals on

carbon form three sp2 hybrid orbitals.

C

A trigonal planar atom has sp2 hybridization.

The three hybrid orbitals form the points of a triangle.

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Double Bonds

C C

H

H

H

H

The three sp2 hybrid orbitals of carbon and 1s orbitals of hydrogen make up the σ-framework of ethene.

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Double Bonds

When the double bond is formed between the two carbons of ethene, a different type of bond is needed (a π bond). This bond is formed with the remaining 2pz orbitals and is higher energy than the σ bonds.

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