Covalent Bonding!
Co = Together
The Octet Rule
 The octet rule says that all
atoms want to have eight
valence electrons, like the noble
gases.
 One way that atoms can follow
the octet rule is by giving and
taking electrons… ionic
bonding
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Covalent bonding
 The other way that atoms can follow the octet rule is
by covalent bonding.
 Co means together or sharing, so covalent bonding
happens when atoms share electrons and stick
together.
 Ionic vs. Covalent bonding
When does covalent
bonding happen?
 Well, let’s think about it…
 Ionic bonding—give and
take—happened between way
different, or unequal, atoms.
 When does sharing
(remember co?) usually
happen?
 Between equals???
thenextweb.com
Which brings us back to…
 Remember electronegativity?
 The ability of an atom to attract electrons?
 So if atoms have similar electronegativities they end
up sharing electrons instead of giving and taking
Some numbers to live by
 If two atoms have close to the same
electronegativity, usually a difference between 0.0
and 0.4, they will form non-polar (equally sharing)
covalent bonds.
 If two atoms have a medium difference in
electronegativity, usually between 0.5 and 1.7, they
will form polar (unequally sharing) covalent bonds.
 If two atoms have a large difference in
electronegativity, usually over 1.7, they will form
ionic bonds
PC, NPC, or Ionic
 For the following compounds, determine if the bonding
is ionic, polar covalent, or non-polar covalent.











CO
MgCl2
CH4
BaO
SiO2
CuF2
O2
H2 O
CaBr2
NO
NaOH
Note:
• When a metal and non-metal
bond, they form ionic bonds
(No matter what)!
• When two nonmetals bond,
they form covalent bonds (No
matter what)!
• Two metals don’t bond, they
form alloys
Methane is covalently
bonded
X’s are
Hydrogen
electrons
vinstan.wikispaces.com
Water is covalently bonded
antranik.org
When does covalent
bonding happen?
 Between atoms of the same element (Diatomic
molecules).
 H2
 O2
 Between non-metals
 H2 O
 CH4
 CCl4
 Between non-metals in polyatomic ions
 PO4-3
 CH3COO-1
What are the properties of
covalent molecules?
 Usually liquids or
gases
 Low melting and
boiling points
 Insoluble or very low
solubility in water
(don’t dissolve well)
 Do not conduct
electricity in solution
 Have odor
dreamstime.com
dailyforex.com
allaboutboats.blogspot.com
Ionic vs. covalent
Property
State (at room
temp.)
Melting and
boiling points
Soluble in water
Conduct
electricity when
dissolved in
water
Odor
Ionic (Think
Salt)
Solid
Covalent (Think
gasoline)
Liquid or gas
High
Low
Yes
Yes
No, or low
No
No
Yes
Vocabulary Warning!!!
 You may have noticed I started using the word molecule
instead of compound.
 I wonder why?
 Just trying to confuse you?
 Trying to increase your vocabulary?
 Compound: Two or more different ELEMENTS chemically
bonded.
 Formula unit: Ratio for ionically bonded elements.
 Molecule: Two or more ATOMS covalently bonded.
 What’s this mean for you?
 All covalently bonded chemicals are molecules.
Compound, Molecule or
Both?
 H2O
 Covalent, so molecule
 Two different types of atoms, so compound
 NaCl
 Ionic, so compound
 H2
 Covalent, so molecule
More Compound,
Molecule, or Both?
 CF4
 Covalent, so molecule
 Two different types of atoms, so compound
 C2H5OH
 Covalent, so molecule
 Two different types of atoms, so compound
 MgCl2
 Ionic, so compound
Back to covalent bonding

In covalent bonding, the atoms can share 2 (1 pair) , 4 (2 pair) or even 6
(3 pair) electrons!!!

Single bond: One shared pair of electrons

Double bond: Two shared pairs

Triple bond: Three shared pairs

N2

Double and triple bonds form when an atom needs to share additional
electron pairs to become like a noble gas

Triple bonds are the strongest and the shortest
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