CHE 231 Chapter 1

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Chapter 1: A Review of General

Chemistry, Electrons, Bonds and

Molecular Properties

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1.1 Organic Chemistry• The BIG question: WHY do reactions occur?

– We will need at least 2 semesters of your time to answer

this question

– FOCUS ON THE ELECTRONS

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1.2 Structural Theory• What term do we use to describe different

substances with the same formula?

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1.2 Structural Theory

• Practice with SkillBuilder 1.1: Determining the

Constitution of Small Molecules

• CH4O, CH5N, C4H10O

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•How do potential energy and stability relate?

• What forces keep the bond at the optimal length?

1.3 Covalent Bonding

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• Practice with SkillBuilder 1.2: Drawing the Lewis Dot

Structure of an Atom

• Carbon, Oxygen, Fluorine

1.3 Counting Valence Electrons

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1.3 Simple Lewis Structures•

For simple Lewis Structures… 1. Draw the individual atoms using dots to represent the

valence electrons.

2. Put the atoms together so they share PAIRS of electrons to

make complete octets. WHAT is an octet?3. Connect the hydrogen atoms.

4. Pair any unpaired electrons so that each atom achieves an

octet.

• Practice with SkillBuilder 1.3: Drawing the LewisStructure of a Small Molecule

• Try drawing the structure for C2H2, CH3OH, C3H6

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1.4 Formal Charge

or

• Practice with SkillBuilder 1.4: Calculating Formal Charge

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1.5 Polar Covalent Bonds

• Can a bond have both covalent and ionic character?

• Practice with SkillBuilder 1.5 Locating Partial Charges

Resulting from Induction

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1.6 Atomic Orbitals

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1.6 Atomic Orbitals• Practice with SkillBuilder 1.6: Identifying Electron

Configurations• Carbon, Oxygen, Sulfur

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• According to Valence Bond Theory, only constructive

interference results in a bond

1.7 Valence Bond Theory

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1.9 Hybridized Atomic Orbitals

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• Consider ethene (ethylene), C2H4.


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• An sp2 hybridized carbon will have three equal-energy

sp2 orbitals and one unhybridized p orbital

• Which is lower in energy, the sp2 or the p? Why?

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• The sp2 atomic orbitals overlap to form sigma (σ) bonds

• Sigma bonds provide maximum HEAD-ON overlap

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1.9 Hybridized Atomic Orbitals• The unhybridized p orbitals in ethene form pi (π) bonds,

SIDE-BY-SIDE overlap

• Practice with conceptual checkpoint 1.20

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1.9 Hybridized Atomic Orbitals• Consider ethyne (acetylene).

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• The sp atomic orbitals overlap HEAD-ON to form sigma

(σ) bonds while the unhybridized p orbitals overlap SIDE-BY-SIDE to form pi bonds

• Practice with

SkillBuilder 1.7

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• Practice with SkillBuilder 1.7: Identifying Hybridization

States

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1.9 Hybridized Atomic Orbitals• Which should be stronger, a pi bond or a sigma bond?

WHY?

• Which should be longer, an sp3 – sp3 sigma bond overlap

or an sp – sp sigma bond overlap?

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1.10 Geometry Summary

•Practice withSkillBuilder

1.8

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1.10 Geometry Summary

• Practice with SkillBuilder 1.8: Predicting Geometry

• Predict the geometry for all atoms except hydrogen inthe compound below:

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1.11 Molecular Polarity• For molecules with multiple polar bonds, the dipole

moment is the vector sum of all of the individual bonddipoles

• CH2Cl

2, H

2O

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1.11 Molecular Polarity

• Practice with SkillBuilder 1.9: Identifying the Presence

of Molecular Dipole Moments

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1.8 Molecular Orbital Theory• Comparing a H2 molecule versus a He2 molecule. How do

the molecular orbitals (MO) compare to one another?

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1.12 Intermolecular Forces

• Neutral molecules (polar and nonpolar) are attracted to

one another through…

– Dipole-dipole interactions

– Hydrogen bonding

– Dispersion forces (a.k.a. London forces or fleeting dipole-

dipole forces)

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1.12 Dipole-Dipole

• Why do isobutylene and acetone have such different MP

and BPs?

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1.12 Hydrogen Bonding• Explain why the following isomers have different boiling

points

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1.12 Hydrogen Bonding• H-bonds are among the

forces that cause DNAto form a double helix

and some proteins to

fold into an alpha-helix

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1.12 London Dispersion Forces• The result is a fleeting attraction between the two

molecules

• Such fleeting attractions are generally weak.

• But like any weak attraction, if there are enough of

them, they can add up to a lot

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1.12 London Dispersion Forces• The greater the surface area of a molecule, the more

temporary dipole attractions are possible• Consider the feet of Gecko. They have many flexible

hairs on their feet that maximize surface contact

•The resulting London dispersion forces arestrong enough to support the weight of the

Gecko

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1.12 London Dispersion Forces• Practice with SkillBuilder 1.10: Predicting Physical

Properties of Compounds Based on Molecular Structure• Arrange the following compounds in order of increasing

boiling point:

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1.13 Solubility• We use the principle, like-dissolves-like

• Polar compounds generally mix well with other polarcompounds

– If the compounds mixing are all capable of H-bonding and/or

strong dipole-dipole, then there is no reason why they

shouldn’t mix

• Nonpolar compounds generally mix well with other

nonpolar compounds

– If none of the compounds are capable of forming strong

attractions, then no strong attractions would have to be

broken to allow them to mix

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1.13 Solubility

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Additional Example Problems• Draw the structure for C

2

Cl3

N

• Draw the structure for CH2O

• Draw the structure for CH2O2

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Additional Example Problems• Give all formal charges in the structures below.

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Additional Example Problems• Analyze the geometry, polarity and types of

intermolecular attractions for the following molecules.

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CHE 231 Chapter 1

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