2. • 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
3. 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
4. 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
7. • 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
8. • Ionic compounds are formed when an electropositive
element transfers electron(s) to an electronegative
element
9. Covalent Compounds
• Equal sharing of electrons: nonpolar covalent bond
(e.g., H2)
• Sharing of electrons between atoms of different
electronegativities: polar covalent bond (e.g., HF)
11. • 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
12. Lewis Structure
Formal charge =
number of valence electrons –
(number of lone pair electrons +1/2 number of bonding electrons)
17. Molecular Orbitals
• Molecular orbitals belong to the whole molecule
• σ bond: formed by overlapping of two s orbitals
• Bond strength/bond dissociation: energy required to
break a bond or energy released to form a bond
23. The orbitals used in bond formation determine the
bond angles
• Tetrahedral bond angle: 109.5°
• Electron pairs spread themselves into space as far from
each other as possible
34. Summary
• A π bond is weaker than a σ bond
• The greater the electron density in the region of orbital
overlap, the stronger is the bond
• The more s character, the shorter and stronger is the
bond
• The more s character, the larger is the bond angle
35. The vector sum of the magnitude and the direction of the individual
bond dipole determines the overall dipole moment of a molecule
Molecular Dipole Moment
36. Brønsted–Lowry Acids and Bases
• Acid donates a proton
• Base accepts a proton
• Strong reacts to give weak
• The weaker the base, the stronger is its conjugate acid
• Stable bases are weak bases
37. An Acid/Base Equilibrium
Ka: The acid dissociation constant
H2O + HA H3O+
+ A-
[H3O+
][A-
]
Ka =
[H2O][HA]
pKa = -log Ka
38. The Henderson–Hasselbalch Equation
• A compound will exist primarily in its acidic form at a pH
< its pKa
• A compound will exist primarily in its basic form at a pH
> its pKa
• A buffer solution maintains a nearly constant pH upon
addition of small amount of acid or base
[ ]
[ ]−
+=
A
HA
logpHp aK
The pH indicates the concentration of hydrogen ions (H+
)
39. • When atoms are very different in size, the stronger
acid will have its proton attached to the largest atom
40. • When atoms are similar in size, the stronger acid will
have its proton attached to the more electronegative
atom
• Inductive electron withdrawal increases the acidity of a
conjugate acid
41. Acetic acid is more acidic than ethanol
CH3COH
O
CH3CH2OH
pKa = 4.76 pKa = 15.9
acetic acid ethanol
The delocalized electrons in acetic acid are shared by
more than two atoms, thereby stabilizing the conjugated
base
CH3CO-
O
CH3CO-
O
42. • Lewis acid: non-proton-donating acid; will accept two
electrons
• Lewis base: electron pair donors
Lewis Acids and Bases