•The atoms held
together by
sharing
electrons are
joined by a
Covalent Bond.
2. Covalent bonds-
Two atoms share one or more pairs of outer-shell
electrons.
Oxygen Atom
Oxygen Atom
Oxygen Molecule (O2)
Molecules and Molecular
Compounds
• Molecule is a neutral
group of atoms joined
together by covalent
bonds.
• Diatomic molecule is a
molecule consisting of
two atoms.
• A compound composed
of molecules is called a
molecular compound.
Properties
• Molecular compounds tend to have
relatively lower melting and boiling points
than ionic compounds.
– Many are gases or liquids at room
temperature.
– Most are formed from atoms of two or more
nonmetals.
Molecular Formulas
• A molecular formula is the chemical
formula of a molecular compound.
• It shows how many atoms of each element
a molecule contains.
• CO2
Carbon Dioxide
• 1 Carbon Atom
• 2 Oxygen Atoms
• Ionic Vs. Covalent Bond
So
what
are
covalent
bonds?
In covalent bonding,
atoms still want to achieve
a noble gas configuration
(the octet rule).
In covalent bonding,
atoms still want to achieve
a noble gas configuration
(the octet rule).
But rather than losing or gaining
electrons,
atoms now share an electron pair.
In covalent bonding,
atoms still want to achieve
a noble gas configuration
(the octet rule).
But rather than losing or gaining
electrons,
atoms now share an electron pair.
The shared electron pair
is called a bonding pair
Chlorine
forms
a
covalent
bond
with
itself
Cl2
Cl
Cl
How
will
two
chlorine
atoms
react?
Cl
Cl
Each chlorine atom wants to
gain one electron to achieve an octet
Cl
Cl
Neither atom will give up an electron –
chlorine is highly electronegative.
What’s the solution – what can they
do to achieve an octet?
Cl
Cl
Neither atom will give up an electron –
chlorine is highly electronegative.
What’s the solution – what can they
do to achieve an octet?
Cl Cl
octet
Cl Cl
octet
circle the electrons for
each atom that completes
their octets
Cl Cl
The octet is achieved by
each atom sharing the
electron pair in the middle
circle the electrons for
each atom that completes
their octets
Cl Cl
The octet is achieved by
each atom sharing the
electron pair in the middle
circle the electrons for
each atom that completes
their octets
Cl Cl
This is the bonding pair
circle the electrons for
each atom that completes
their octets
Cl Cl
It is a single bonding pair
circle the electrons for
each atom that completes
their octets
Cl Cl
It is called a SINGLE BOND
circle the electrons for
each atom that completes
their octets
Cl Cl
Single bonds are abbreviated
with a dash
circle the electrons for
each atom that completes
their octets
Cl Cl
This is the chlorine molecule,
Cl2
circle the electrons for
each atom that completes
their octets
Naming Covalent Compounds
Covalent compounds are named by adding prefixes to the
element names.
The compounds named in this way are binary covalent compounds.
‘Binary’ means that only two atom are present.
‘Covalent’ (in this context) means both elements are
nonmetals.
A prefix is added to the name of the first element in the formula if
more than one atom of it is present. (The less electronegative
element is typically written first.)
A prefix is always added to the name of the second element in the
formula. The second element will use the form of its name ending
in ‘ide’.
Naming Covalent Compounds
Prefixes
Subscript
Subscript
2
3
Prefix
monoditri-
7
8
Prefix
hexaheptaocta-
4
5
tetrapenta-
9
10
nonadeca-
1
6
Note: When a prefix ending in ‘o’ or ‘a’ is added to ‘oxide’, the
final vowel in the prefix is dropped.
Naming Binary Covalent Compounds:
Examples
1
mono
2
di
3
tri
4
tetra
5
penta
6
hexa
7
heptaa
8
octa
9
nona
10
deca
* Second element
in ‘ide’ from
* Drop –a & -o
before ‘oxide’
N2S4
dinitrogen tetrasulfide
NI3
nitrogen triiodide
XeF6
xenon hexafluoride
CCl4
carbon tetrachloride
P2O5
diphosphorus pentoxide
SO3
sulfur trioxide
Classifying Compounds
Classifying a compound using its name is not as difficult as
using its formula.
The names of covalent compounds will be easily recognized by
the presence of the prefixes (mono-, di-, tri-, etc.).
If no prefixes are present in the name, the compound is ionic.
(Exception: some polyatomic ion names always contain
prefixes (such as dichromate) but those will be memorized
and recognized as ions.)
Writing Formulas for Covalent
Compounds
The names of covalent compounds contain prefixes that indicate
the number of atoms of each element present.
If no prefix is present on the name of the first element, there is only
one atom of that element in the formula (its subscript will be 1).
A prefix will always be present on the name of the second element.
The second element will use the form of its name ending in
Remember:
 The compounds named in this way are binary covalent
compounds (they contain only two elements, both of which are
nonmetals).
 When in covalent compounds, atoms do not have charges.
Subscripts are determined directly from the prefixes in the name.
Writing Formulas for Binary Covalent
Compounds: Examples
1
mono
2
di
3
tri
4
tetra
5
penta
6
hexa
7
heptaa
8
octa
9
nona
10
deca
* Second
element in
‘ide’ from
* Drop –a & -o
before ‘oxide’
nitrogen dioxide
NO2
diphosphorus pentoxide
P2O5
xenon tetrafluoride
XeF4
sulfur hexafluoride
SF6