Covalent Bonding and Lewis Dot
Structures
Covalent Bonding
• A chemical bond is the force that holds two or more
atoms together and makes them function as a unit
• Atoms form bonds to become most stable
• Covalent Bonding: Electrons are shared between two or
more elements. Always between 2 non-metals
– The bonding results from mutual attraction of the two
nuclei for the shared electrons
– Not all electrons are shared in a covalent bond. The
unshared electrons are called lone pairs.
• How is covalent bonding different than ionic bonding?
Prefixes for Covalent Bonding
Prefix
Number Indicated
Mono-
1
Di-
2
Tri-
3
Tetra-
4
Penta-
5
Hexa-
6
Hepta-
7
Octa-
8
Rules for Naming Compounds
1. The first element in the formula is named first,
and the full element name is used.
2. The second element is named as though it were
an anion.
3. Prefixes are used to denote the numbers of
atoms present.
4. The prefix mono- is never used for naming the
first element. For example, CO is called carbon
monoxide, NOT monocarbon monoxide.
5. Prefix(not mono)1st element space prefix2nd
element
Naming Covalent Compounds
Examples
• BF3
– Rule 1: Name the first element, using the full
element name: boron.
– Rule 2: Name the second element as though it
were an anion: Fluoride
– Rule 3 and 4: Use prefixes to denote numbers of
atoms. One boron atom: do not use mono- in first
position. Three fluorine atoms: use prefix tri-.
– The name is boron trifluoride.
Covalent Compounds
• Name the following covalent compounds:
1.
2.
3.
4.
5.
6.
7.
8.
NO
N2O5
CO2
SiO3
CCl4
IF5
PCl5
P4O6
Write the formulas for the following
Covalent Compounds
•
•
•
•
•
Carbon Monoxide
Carbon tetrafluoride
Dinitrogen Trioxide
Selenium dioxide
Nitrogen Monoxide
Diatomic Molecules
• Diatomic molecules: A molecule composed of two atoms
• You must memorize the following diatomic molecules
Name
Formula
Hydrogen
H2
Nitrogen
N2
Oxygen
O2
Fluorine
F2
Chlorine
Cl2
Bromine
Br2
Iodine
I2
Lewis Structures
• A Lewis Structure is a representation of a molecule or
polyatomic ion showing how valence electrons are
arranged among the atoms in the molecule or ion.
• In writing Lewis Structures, we ONLY include valance
electrons
• Electrons involved in bonding are called bonding pair.
Electrons not involved in bonding are called lone pairs
or unshared pairs
• Keep in mind the octet rule when drawing Lewis
structures
– Exceptions to the octet rule:
• Hydrogen and helium only need a duet
Steps for Writing Lewis Structures
1. Calculate the sum of the valence electrons from all of
the atoms. Do not worry about keeping track of which
electrons come from which atoms. It is the total
number of valence electrons that is important.
2. Use one pair of electrons to form a bond between
each pair of bound atoms. For convenience, a line
(instead of a pair of dots) is often used to indicate
each pair of bonding electrons (central atoms are
named first)
3. Arrange the remaining electrons to satisfy the duet
rule for hydrogen and the octet rule for all other
elements. Always start with the central atom.
Lewis Structures
• Write the Lewis Structure for water:
• Step 1: find the sum of the valence electrons for H2O:
1 + 1 + 6 = 8 valence electrons
• Using a pair of electrons per bond, we draw in the two O-H bonds,
using a line to indicate each pair of boding electrons:
H-O-H
• We arrange the remaining electrons around the atom to achieve a
noble gas electron configuration for each atoms. Remaining
electrons = number of total valance electrons – number of
electrons used in bonds (2 per bond)
– Water has used 4 electrons for bonds so we have 4 remaining
electrons (8-4=4)
• How many lone pairs does water have?
Lewis Structure
• Draw the Lewis Structure for the following
molecules:
• CCl4
• PH3
Lewis Structures with Multiple Bonds
•
•
•
•
•
Lets do the Lewis Structure for Carbon Dioxide
Total valence electrons: 4 + 6 + 6 = 16
Form Bonds: O-C-O
Remaining electrons: 16-4 = 12
Distribute remaining electrons:
• Is this correct? (Did we use 16 electrons? Is every octet filled?)
– No not all octet is filled
• We need a double or triple bond
• Correct Lewis Structures:
• Having multiple possible valid structures is referred to as having
resonance
• Lewis structure for polyatomic ions must have an overall charge. The
charge is denoted by brackets and a charge outside of the brackets
Bonds
• Single Bond- a covalent bond in which one pair of electrons is
shared by two atoms
• Double Bond- A covalent bond in which two pairs of electrons are
shared by two atoms
• Triple Bond- A covalent bond in which three pairs of electrons are
shared by two atoms
• No more than 3 pairs can be shared
• Lewis structure for polyatomic ions must have an overall charge.
The charge is denoted by brackets and a charge outside of the
brackets
– How do you determine the total number of valance electrons in a
polyatomic ion?
• Add the total valance electrons like normal and subtract the charge of the ion
Examples
• Draw Lewis structure for the following molecules
1. HF
2. N2
3. NH3
4. CH4
5. CF4
6. NO+
7. NO3-