Covalent Bonds
CHAPTER 9
REVIEW

Octet rule – all atoms want to have 8 electrons
in their outer shell
 Exception
– helium (2)
 Noble gases – very stable

Binary ionic compounds – cations and anions
lose or gain e Resulting
ions have noble gas configuration
COVALENT BONDS
Chemical bond where elements share valence
electrons to gain noble gas configuration
 Usually occurs between elements that are close
to each other on the periodic table

 Majority
 CO2
 H 2O
 SiO2
are nonmetallic elements
MOLECULES

Molecule – forms when two or more atoms are
bonded covalently
 Carbohydrates,
synthetic fibers

proteins, fats, DNA, wool, cotton,
Diatomic molecules – elements not found in
nature as single atom because more stable this
way
 H2,
N2,O2, F2,Cl2,Br2,I2
 Share one pair of valence electrons
SINGLE COVALENT BONDS
Formed when a single pair of e- is shared
between two bonded atoms
 Shared pair - bonding pair
 Lewis structures – use electron dot diagrams to
show how electrons are arranged in molecules

 Single
bond is represented by two dots or a single
line
 Example: H2
 H:
H or H—H
MULTIPLE COVALENT BONDS
Form when more than more than one pair of eis shared between two bonded atoms
 # valence electrons of an element is associated
with the number of shared electron pairs
needed to complete the octet
 Double bond = 2 e- pairs being shared (2 lines)
 Triple bond = 3 e- pairs being shared (3 lines)

SIGMA BONDS

Sigma bond (σ) - single covalent bonds
 Results
if atomic orbitals overlap end to end
concentrating the e- in a bonding orbital between
the two atoms
 Bonding orbital - Localized regions where bonding
electrons most likely found

Form when:
S
orbital overlaps another s orbital
 S orbital with p orbital
 P orbital with p orbital
REMEMBER ORBITALS?
PI BONDS
Pi bonds (π) form when parallel orbitals overlap
to share electrons
 Double covalent bond:

1

sigma bond and 1 pi bond
Triple covalent bond:
1
sigma bond and 2 pi bonds
PICTURE OF PI BOND
STRENGTH OF COVALENT BONDS

Bond length – distance between two bonding
nuclei at the position of maximum attraction
 Determined
by size of atom and how many electron
pairs are shared
 Inverse relationship between # if electron pairs
shared and bond length
 single bonds weaker than double…. Etc.
 F2
bonds weaker than N2
STRENGTH OF COVALENT BONDS

Bond dissociation energy – amount of energy
required to break a specific covalent bond
 Direct
relationship between bond energy and bond
length
 Bonded closer together – takes more energy to
separate