Aim: What are coordinate
covalent bonds?
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OTHERS.
Coordinate Covalent Bonds
• A coordinate bond (also called a dative covalent bond)
is a covalent bond (a shared pair of electrons) in
which both electrons come from the same atom.
• A coordinate covalent bond is usually shown with an
arrow.
Coordinate Covalent Bond
• When one atom donates both electrons in a
covalent bond.
• Carbon monoxide
• CO
C O
Coordinate Covalent Bond
When one atom donates both electrons
in a covalent bond.
 Carbon monoxide
 CO

C O
Coordinate Covalent Bond
When one atom donates both electrons
in a covalent bond.
 Carbon monoxide
 CO

C
O
General Rules
1. Select the central atom (atom in the middle); the least
electronegative atom (H and halogens will not be central
atoms)
2. Count the total number of valence electrons there should be.
3. Put one bond between each atom. Put the rest of the valence
electrons on the outer atoms.
4. Check if every atom fulfills octet. If not move paired electrons
to fulfill octet.
5. Recount the number of total shared valence electrons.
Example 2
• N2O
Polyatomic Ions
• A polyatomic ion is a tightly bound group of atoms that has a
positive or negative charge and behave as a unit.
• A group of atoms that are covalently bound and as a whole
have a charge.
Which compound contains both ionic and
covalent bonds?
1.
2.
3.
4.
HBr
CBr4
NaBr
NaOH
Practice
1. Draw the electron dot structure for the polyatomic boron
tetrafluoride anion (BF4-)
Practice
2. Draw the electron dot structure for the hydrogen carbonate
ion (HCO3-). Carbon is the central atom, and hydrogen is
attached to oxygen in this polyatomic anion.
Exceptions to Octet Rule
• The octet rule cannot be satisfied whose total number of
valence electrons is an odd number. There are also
molecules in which an atom has fewer, or more, than a
complete octet in the valence electrons.
Example 1
• Boron has a tendency to form compounds in which it has an
incomplete octet. For example BF3
Example 2
• Atoms of elements in the third or higher periods can exceed
their octet as they have d orbitals available for bonding. For
example SF6
• http://www.kentchemistry.com/links/bonding/covalentlewisdot.htm