Note: Chapter 1 is about 23-25 pages long, I condensed it into • The three
about 4 pages, and it has all the main points, every bolded
word and even pictures when possible. It took me a long time orbitals within a given shell
to pick out the necessary parts and make it all neat like this so are oriented in
hopefully it’s useful! All images are courtesy of google space along
images. mutually perpendicular
Structure and Bonding
px, y and pz.
Organic chemistry is the study of carbon compounds its Each p orbital is separated
position in the periodic table and electronic structure makes it by a region
peculiar.As a group 4Aelement, carbon can share four of zero electron density called a
valence electrons and form four strong covalent bonds. They
can chain together, and is able to form a huge array of
compounds, from methane to DNA.
• 1.1 Atomic Structure: The Nucleus • 1.3Atomic
• Nucleus consists of positive subatomic particles called Configurations
protons, which are electrically neutral. There are an
even number of negatively charged electrons as the • The lowest-energy
protons. arrangement, or
• 10e typical atom is around 200 picometers, or 2 x 10 ground-state electron
m in diameter. configuration of an atom is a listing of the orbitals
• Atomic number (Z) gives the number of occupied by its electrons…We predict this
protons/electrons it contains, and mass number (A) arrangement via:
which gives the total number of protons plus neutrons
in its nucleus. Rule 1: Lowest energy orbitals fill up first, 1s -> 2s ->
• Atoms with the same atomic number but different 2p -> 3s -> 3p -> 4s ->3d, called the aufbau principle.
mass numbers are called isotopes.
Rule 2: Electrons act as if they spin around an axis;
this spin can have two orientations, up or down,(
• 1.2 Atomic Structure: Orbitals ↑ or ↓
) and only two electrons can occupy an orbital,
• How are electrons distributed? – According to the of opposite spin, called Pauli exclusion principle.
quantum mechanical model, the behavior of a specific
electron can be described in a mathematical equation Rule 3: If two or more empty orbitals of equal energy
called a wave equation – the solution to the equation is are available, electrons occupy spins parallel until all
called a wave function or an orbital noted as the orbitals are half-full, called the Hund’s rule.
Greek letter psi .
• We plot Ψ 2in 3-D space, and find that an orbital • 1.4 Development of Chemical Bonding Theory
describes a volume of space around a nucleus that an • In 1858,August Kekule andArchibald Couper
electron is most likely to occupy. I.e Imagine looking
at a photograph of an electron with low shutter speed, independently proposed that carbon is tetravalent and
the image would look like a blurry cloud, indicating always forms four bonds when joining other elements
where the electron has been. to form stable compounds, and can even form
• The different orbitals are denoted s, p, d and f, each
with a different shape. S orbitals are spherical, p
orbitals are dumbbell-shaped, and 4 of 5 d orbitals are
cloverleaf-shaped, while the fifth just looks like a
dumbbell with a doughnut in the middle.
• Orbitals are organized into electron shells centered
around the nucleus gaining successive size and energy
as the shell #increases. The first shell contains a
single s orbital (1s), and thus holds only 2
electrons, the second shell contains one 2s orbital
and three 2p orbitals thus 8 electrons. • This view was two dimensional, and until 1874, the
third dimension was not proposed, and that the four
bonds of carbon are in fact not random, but have
specific spatial directions.
• Why do atoms bond together, and how can the bonds
be described electronically. The why is easy, atoms
bond because the resultant compounds are usually
more stable and lower in energy energy, usually heat,
always flows out of the chemical system when a bond
forms, and is always needed to be put in to break a
bond. The how is tricky without knowing more about
the electronic properties of atoms.
• The atom’s outermost shell, or valence shell, imparts
special stability to the noble gases, and that main-
group elements tend to take on electron configuration
• To describe how electron sharing leads to bonds
of the nearest noble gas. i.e) lithium, group 1A, tends between atoms, two models have been developed to
to lose an s electron to achieve noble-gas describe covalent bonding: valance bond theory and
configuration as a cation. Chlorine, a group 7A
element tends to gain a p electron to fill the valence molecular orbital theory.
shell and form an anion. The resultant ions, Li Cl are • According to the valence bond theory which is easier
to visualize, a covalent bond forms when two atoms
held together by electrostatic attraction called an ionic approach each other closely and a singly occupied
bond. orbital on one atom overlaps a singly occupied orbital
on the other atom. The electrons are now paired in the
• Elements in the middle of the periodic table, like overlapping orbitals and are attracted to the nuclei of
carbon are different. CH 4 methane, is not ionic, but both atoms, thus bonding the atoms together.
rather electrons are shared in something called a • (The H-H bond results from the overlap of two singly
covalent bond. The natural collection of atoms held occupied hydrogen 1s orbitals)
together by these bonds are called molecules.
• The H-H bond is cylindrically symmetrical such
• We can indicate bonds, when formed by the head on overlap of two
covalent bonds in
atomic orbitals along a line drawn between the nuclei,
are called sigma bonds.
• Since the product, H2has 436 kJ/mol less energy than
the two starting H atoms, the product is more stable
than the reactants, meaning H-H has a bond strength
of 436 kJ/mol. AKAwe need to put that much energy
molecules via Lewis Stuctures, or electron-dot into the H-H bond to break it apart.
structures, where valence shell electrons are • Bond length refers to the optimum distance between
represented as dots. Even simpler is the Kekule nuclei leading to maximum stability.
structure, or line-bond structure, where two-electron
covalent bonds are indicated as lines between atoms. 3
• 1.6 sp Hybrid Orbitals and the Structure of
• Valence electrons that are not used for bonding are
called lone-pair electrons, or non-bonding electrons. • Bonding in hydrogen molecules seems to be pretty
simple…however the situation becomes complicated
in organic molecules with tetravalent carbon atoms.
• 1.5 Describing Chemical Bonds: Valance Bond For example, methane, CH , 4as four valence
Theory electrons (2s 2p ) and forms four bonds. Two different orbital types means two different bonds, • Imagin