2018/02/20
CHEMICAL BONDING AND
MOLECULAR STRUCTURE
MOLECULAR STRUCTURE, BONDING AND
PROPERTIES OF MOLECULES
This enable the scientists to group the molecules
according to the properties that is shown by their
geometries.
One have to understand the
electronic geometry (Electron pair geometry)
before the
molecular geometry.
RULES FOR DRAWING LEWIS OR COUPER
STRUCTURE
These rules are also called electron-bookkeeping:
1.(a) Write down the chemical formula of that
molecule.
1. (b) Calculate the total valence electrons (TVE) of all
the atoms forming that molecule.
2. Identify the central atom.
This must be the least electron negative (the most
electro-positive) atom.
3. Draw the skeleton of the that molecule.
4. Form a bond between each ligand (domains) and
the central atom.
CHEMICAL BONDING AND MOLECULAR STRUCTURE
Chemical bonding is a bond between atoms in
compound.
Molecular structure is also called a molecular
geometry because it shows the geometry or the
structure of the molecule/s that is formed when the
ligands (domains) are repelling each other or one
another around the central atom during bonding.
It may also shows the geometry or the structure of
the molecule/s that is formed when the ligands
(domains) are repelling lone pairs around the central
atom during bonding.
CHEMICAL BONDING AND MOLECULAR
STRUCTURE
The rules of drawing Lewis dot , Lewis line or Couper
structure must be known.
Then you can identify an electronic structure.
From the electronic structure, the 3-dimentional
(3-D) can be easily drawn which will guide you to the
molecular geometry.
RULES FOR DRAWING LEWIS OR COUPER STRUCTURE
5. Put the electrons around each ligand
until it attain the octet configuration.
Do not forget the exceptions: e.g.
(a)(i) F atom is always a ligand
(a)(ii) H atom is always a ligand
(b) H atom is surrounded by 2 electrons.
(c)In an oxyacid, the H of an oxyacid is
attached to the oxygen of an oxyacid.
Example: HNO3
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RULES FOR DRAWING LEWIS OR COUPER STRUCTURE
Examples of the exceptions:
(c) Be atom is surrounded by 4 electrons.
(d) B atom is surrounded by 6 electrons.
(e) If the central atom is from period 3 or
above it can exceed the octet rule.
(f) The atoms of group 8 elements are
always central atoms.
RULES FOR DRAWING LEWIS OR COUPER
STRUCTURE
(b) If the central atom is not satisfied and the
electrons are not finished, then check if the central
atom is from period 3 or above then put these
electrons around the central atom as these electrons
will be located in the d-orbital of that atom.
(c) If the central atom is not satisfied and the
electrons are finished, then form a double bond
between the central atom and a/the ligand/s until the
central atom is satisfied.
RULES FOR DRAWING THE 3-DSTRUCTURE
Check if the molecule is a :
AX2
AX3
AX2L
AX4
AX3L
AX2L2
2 Region molecules
3 Region molecules
4 Region molecules
Where A is a central atom, X a ligand and L a lone pair.
RULES FOR DRAWING LEWIS OR COUPER
STRUCTURE
6. Subtract the electrons used in 5 above from the
TVE.
7. Put the remaining electrons around the central
atom until it attain its octet configuration.
(a) Again remember the exception.
(b) If the central atom is from period 3 or above it can
exceed the octet configuration.
8. (a)If the central atom is satisfied and the electrons
are finished, then you are done.
RULES FOR DRAWING LEWIS OR COUPER
STRUCTURE
8. (a) For a negatively charged molecule (polyatomic
anion); the extra electron must be added to the most
electronegative atom.
(b) For a positively charged molecule (polyatomic
cation); the extra electron must be subtracted from
the least electronegative atom.
RULES FOR DRAWING THE 3-DSTRUCTURE
Check if the molecule is an :
AX5
AX4L
AX3L2
AX2L3
AX6
AX5L
AX4L
etc.
5 Region molecules
6 Region molecules
Where A is a central atom, X a ligand and L a lone pair.
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