General Chemistry 1

1. COVALENT
COMPOUND
GENERAL CHEMISTRY 1 - WEEK 3

2. LEARNING OBJECTIVES:
1. illustrate how covalent compounds are formed
2. apply the octet rule in the formation of covalent
compounds
3. draw the Lewis structure of covalent compounds
4. draw the resonance structures of covalent compounds
5. describe some exceptions of the octet rule
6. name covalent compounds given their formula and write
formula given the name of covalent compounds
7. identify covalent compounds that are used in everyday
living

3. KEY CONCEPTS
- COVALENT COMPOUNDS are formed when a pair of electrons are shared
between
nonmetals.
- OCTET RULE states that when atoms gain, lose, or share electrons to form
bonds
with other atoms they tend to achieve the electron configuration of the
noble gas
nearest to them with eight valence electrons.
- There are three types of covalent bonds namely SINGLE BOND, DOUBLE
BOND and TRIPLE BOND.
- Bonding electrons are electrons shared between atoms.
- Nonbonding electrons are electrons that does not participating in bonding
or not shared between other atoms

4. Step 1. Determine the valence electrons of
every atom involved.
Step 2. Get the sum of the all the valence
electrons of atoms.
Step 3. Use a pair of electrons to form a single
bond between atoms.
Step 4. Arrange the remaining electrons
around the atom to satisfy the octet rule
except for Hydrogen which is stable with 2
valence electrons.
- Steps in drawing the Lewis structures of compounds
- LEWIS STRUCTURE
shows how electrons
are arranged in an
atom.

6. Example: Draw the Lewis structure of F2
Step 1. Determine the valence electrons of every atom involved.
Fluorine from group 7 (7 valence electrons)
Step 2. Get the sum of the all the valence electrons of atoms.
Total valence electrons:
Fluorine = 7 valence electrons x 2 atoms
=14 electrons
Step 3. Use a pair of electrons to form a single bond between atoms
F —F
(—)single line bond is equivalent to 2 electrons
14 electrons – 2 electrons = 12 electrons

7. Step 4. Arrange the remaining electrons around the atom to
satisfy the octet rule except for Hydrogen which is stable
with 2 valence electrons
Check: Count the number of valence electrons whether each atom of Fluorine
satisfies the octet rule.
Fluorine = bonding electrons + nonbonding electrons
Fluorine = (1 x 2 e-) + 6 e-
Fluorine = 2 e- + 6 e-
Fluorine = 8 e-

8. Step 1. Carbon from group 4A (4 valence electrons);
Chlorine from group 7A (7 valence electrons)
Step 2. Carbon = 4 valence electrons x 1 atom
=4 electrons
Chlorine = 7 valence electrons x 4 atoms
= 28 electrons
Total valence electrons = 4 e-+28 e-
= 32 e-
Step 3. The least electronegative atom occupies the central position.
Example: Draw the Lewis structure of CCl4

9. Step 4.
Check: Count the number of valence electrons whether each atom satisfies the octet rule.
Carbon = bonding electrons + nonbonding electrons
Carbon = (4 x 2e- + 0
Carbon = 8 e-
Chlorine = bonding electrons + nonbonding electrons
Chlorine = (1 x 2 e-+ e-
Chlorine = 2 e- + 6 e-
Chlorine = 8 e-

10. Example: Draw the Lewis structure of CO2
Step 1. Carbon (4 valence electrons); Oxygen (6 valence electrons)
Step 2. Carbon = 4 valence electrons x 1 atom
=4 electrons
Oxygen = 6 valence electrons x 2 atoms
= 12 electrons
Total valence electrons = 4 e- + 12 e-
=16 e-
Step 3. The least electronegative occupies the central position
O—C—O

11. Step 4:

12. Check: Count the number of valence electrons whether
each atom satisfies the octet rule.
Carbon = bonding electrons + nonbonding electrons
Carbon = 4 x 2e-
Carbon = 8e-
Oxygen = bonding electrons + nonbonding electrons
Oxygen = (2 x 2e-)+4e-
Oxygen = 8e-

13. LEWIS STRUCTURE AND RESONANCE

14. EXCEPTIONS TO THE OCTET RULE
- The octet rule has limitations in many situations involving covalent bonding.
These exceptions to the octet rule are of three main types:
1. Molecules with fewer than an octet of valence electrons.
This type of exception occurs when there are fewer than eight valence
electrons around the central atom. An example of this case is BeH2, Beryllium
Hydride.
H— Be— H
There are only 4 electrons around Be atom.

15. 2. Molecules containing an odd number of electrons.
Nitric oxide (NO) and nitrogen dioxide (NO2) are examples of molecules with odd
number of electrons which do not follow the octet rule.
3. Molecules with more than an octet of valence electrons.
Elements along the 3rd period and beyond have 3d orbitals that can
participate in chemical bonding. Hence, it is possible for the central atoms
from 3rd period and beyond to have expanded. Sulfur hexafluoride (SF6) and
phosphorus pentachloride (PCl5) are examples of compound having more
than 8 electrons around the central atom.

17.  For binary compound, state the name of the first element while the name
of the second element end in -ide.
Example:
HCl - Hydrogen chloride
HF - Hydrogen fluoride
 Prefixes are added to the name of the element to denote the number of
atoms present. For the first element, the prefix “mono” is usually omitted.
When the prefix ends in “a” or “o” and the name of the second element
begins with “a”vowel, the “a” or “o” of the prefix is often dropped.
Guidelines in naming covalent compounds and
writing their formulas:

18. Example 1: Write the name of the following covalent compounds.
NO2 - nitrogen DIoxide
N2O4 - DInitrogen TETRoxide
SF6 - sulfur HEXAfluorid
Example 2: Write the chemical formula of covalent compounds.
sulfur TRIoxide - SO3
DIboron TRIOxide - B2O3
iodine PENTAfluoride - IF5

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