ORGANIC
CHEMISTRY
SUMMARY
NOTES
, Introduction
Friday, 09 October 2020 22:17
• The main types of bonds that exist between atoms are ionic and covalent bonds
• In inorganic compounds, the constituent atoms are held together by ionic bonds, whereas organic
compounds in general are formed because of covalent bonds between atoms
Structure and bonding Page 1
, Principles of atomic
structure
Friday, 09 October 2020 22:18
Wade et al section 1-2
• There are four different types of orbitals, called s, p d and f orbitals, each with a different shape.
• Since organic chemistry is centred on the chemistry of the carbon atom, attention will be given to the s and p
orbitals found in carbon
• The orbitals are found in different electron shells and each successive shell is higher in energy and larger in size than the
previous shell
• the number of orbitals also increases as the shell becomes larger and further removed from the nucleus
• The first electron shell contains only one s-orbital
• The second electron shell has one s-orbital and three p-orbitals, with the p-orbitals pointing towards the x-, y- and z-
axes, respectively
Each orbital can accommodate a maximum of two electrons
• The 2p orbitals are higher in energy than 2s orbitals but the three p-orbitals have the same energy and are called
degenerate orbitals
• Carbon is able to form numerous compounds due to different combinations of the s-and p-orbitals that we will discuss
later
The distribution of electrons of an atom
Electrons that are found in the outermost shell of an atom
Electrons will occupy all orbitals of the same energy before pairing begins
Structure and bonding Page 2
, Chemical bond formation
Friday, 09 October 2020 22:18
Wade et al section 1-3
Observation that main group elements tend to bond in such a way that each atom has eight electrons in its
valence shell, giving it the same electronic configuration as a noble gas
Atoms can form a bond via two modes:
• Due to the electrostatic attraction between ions with opposite charges (ionic bonding)
• By sharing electrons (covalent bonding)
(bond formation or breakage) involves the movement of valence electrons from a region of high
electron density to a region of less electron density
That is, the tendency of an atom to attract a pair of bonding electrons to itself in a molecule,
plays a significant role in the nature of a chemical bond and how it reacts
Structure and bonding Page 3
, Ionic bonding
Saturday, 10 October 2020 00:43
Wade et al section 1-3A
The elements in Group 1A (in the periodic table) each have 1s electron in its outer electron shell. These
elements can lose the one electron to form a cation, which has a filled outer shell, for example the
sodium atom
+
Na Na + 1e
A halogen (Group 7A element) such as a chlorine atom, on the other hand, has seven outer electrons
and when it takes up another electron, the atom obtains an octet such as the formation of the anion
Cl + 1e Cl
The electrostatic attraction between the sodium cation and the chloride anion
Atoms react in such a manner that the non-metals, which are more electronegative elements, tend
to gain electrons to attain the noble gas configuration whereas the metals, which are electropositive
elements, tend to lose electrons to obtain the noble gas configuration (octet).
Increasing EN
Highest EN
Lowest EN
Increasing EN
EN
<0,4 Non-Polar covalent
0-1 Weak Polar covalent
1,1-1,7 Strong Polar covalent
>1,7 Ionic
Structure and bonding Page 4
