Chapter 8
Chemical Bonding: General Concepts
Lattice Energy:
Electron Configuration of ions:
The energy (∆Hf) required to separate
ions of an ionic compound. Example
below showing the relationship
between Ionization Energy and
Electron Affinity relative to the Lattice
Energy.
To determine the Electronic Configuration of
atoms, you must remember that the lowest
energy orbital’s fill before the high level orbitals.
s<p<d<f. This shows that the s subshell will fill
before the p subshell can accept any electrons
and so on. If removing electrons, the electrons
on the highest energy level will be removed
first.
Example: Write the configuration of N3-.
First start with the electronic configuration of
the atom in its ground state.
[He]2s22p3
Three electrons are gained. Therefore, the
electronic configuration of N3- is:
[He]2s22p6
Write the electronic configuration of Sb3+:
Octet Rule:
A rule that states that atoms tend to
lose or gain electrons until their
valence shell contains 8 electrons.
The duet rule applies to [H] and [He]
where there valence shell can only
contain 2 electrons.
[Kr]4d105s25p3 = Sb
Therefore:
[Kr]4d105s2 = Sb3+
Electron Dot Diagram:
A diagram that shows the valence electrons of
an atom, ion or compound .
Formal Charge on an atom:
FC = # of Electrons in valence shell – (Number
of bonds to the atom + # of unshared e )
Polar Covalent Bonds, Bond length and Dipole
Movements:
A bond is said to be polar when the charges on
either end are opposites. Such as a +1 charge on
the right and a -1 charge on the left or a charge
of ±1 on its poles. If this is the case, we can
determine the bond length and the Dipole
Movement (magnitude of its polarity, the
charge on either end).
The formula is
, where q is the charge in
electronic charge units, is the dipole
movement
r is the bond length.
Polar chargeand
example:
HF molecule has a dipole movement of 1.83 D
and a bond length of 91.7 pm. What is the
charge in electronic charge units?
D=Debye = (3.34x10-30 Cm)
Cm
)
C = Columb
M = Metre
q = charge
= Dipole movement
e = electronic charge unit
e = 1.602x10-19 C.
Drawing Lewis Structures:
1. Determine the number of
valence electrons in the
compound.
2. Find central atom.
3. Draw central atom in the
centre.
4. Single bonds to the other
atoms from the central atom,
except in oxoacids, where the
H will bond with the O.
5. Add valence electrons to the
atoms.
6. Add extra double or triple
bonds to satisfy the octet rule
on every atom, including the
central atom.
7. Determine the formal charge
on every atom.
8. If possible, add extra double
or triple bonds to get the
charges closer to zero,
resulting in a more stable
atom.
9. Draw any other resonance
structures (Draw the entire
structure again, only changing
which atoms have the double
or triple bonds to account for
every variant the atom may
have).
10. If there was a charge on the
atom put the structure in
brackets and specify the
charge on upper right hand
corner.