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Organic Chemistry
4
th
Edition
Paula Yurkanis Bruice
Chapter 1
Electronic Structure
and
Bonding
Acids and Bases
Irene Lee
Case Western Reserve University
Cleveland, OH
©2004, Prentice Hall


Organic compounds are compounds containing carbon

Carbon neither readily gives up nor readily accepts
electrons


Carbon shares electrons with other carbon atoms as
well as with several different kinds of atoms
Organic Chemistry

The Structure of an Atom

An atom consists of electrons, positively charged protons,
and neutral neutrons

Electrons form chemical bonds

Atomic number: numbers of protons in its nucleus

Mass number: the sum of the protons and neutrons of an atom

Isotopes have the same atomic number but different mass
numbers

The atomic weight: the average weighted mass of its atoms

Molecular weight: the sum of the atomic weights of all the atoms
in the molecule

The Distribution of Electrons in an Atom

Quantum mechanics uses the mathematical equation of wave
motions to characterize the motion of an electron around a
nucleus

Wave functions or orbitals tell us the energy of the electron and
the volume of space around the nucleus where an electron is
most likely to be found

The atomic orbital closer to the nucleus has the lowest energy

Degenerate orbitals have the same energy

Table 1.1



The Aufbau principle: electrons occupy the orbitals with
the lowest energy first

The Pauli exclusion principle: only two electrons can
occupy one atomic orbital and the two electrons have
opposite spin

Hund’s rule: electrons will occupy empty degenerated
orbitals before pairing up in the same orbital


Ionic compounds are formed when an electropositive
element transfers electron(s) to an electronegative
element

Covalent Compounds

Equal sharing of electrons: nonpolar covalent bond
(e.g., H
2
)

Sharing of electrons between atoms of different
electronegativities: polar covalent bond (e.g., HF)

Electrostatic Potential Maps


A polar bond has a negative end and a positive end

dipole moment (D) = µ = e x d
(e) : magnitude of the charge on the atom
(d) : distance between the two charges
A Dipole

Lewis Structure
Formal charge =
number of valence electrons –
(number of lone pair electrons +1/2 number of bonding electrons)


Important Bond Numbers
H F ICl Br
one bond
O
two bonds
N
three bonds
C
four bonds

The s Orbitals

The p Orbitals

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