MOLECULAR COMPOUNDS

A MOLECULAR COMPOUND is a compound formed when atoms of two or more different
elements share electrons.
o
Molecular compounds are also known as covalent compounds.
o
Molecular compounds form when atoms share a pair of electrons to form a covalent bond.
o
In a covalent bond, the shared electrons are attracted to the nuclei of both atoms.
o
The electrons in a molecular compound are not transferred between atoms, so the atoms
remain uncharged (unlike in an ionic compound, where electrons are transferred between a
metal and a non-metal).
o
Molecular compounds are composed of individual molecules. And, each molecule is
composed of a set number of atoms of each element.

A MOLECULE is a neutral particle composed of two or more atoms joined together by covalent
bonds.
o
A molecule is used to describe two or more atoms of the same element that are joined
together by a covalent bond.
o
These are known as DIATOMIC MOLECULES (they are not compounds). They are:
Hydrogen gas (H2), Nitrogen gas (N2), Oxygen gas (O2), Chlorine gas (Cl2), Bromine gas
(Br2), Iodine gas (I2), and Fluorine gas (F2)

Examples of molecular compounds

All atoms involved in molecular compounds have a COMBINING CAPACITY (the number of
covalent bonds that the atom is able to form a stable molecule).
o
Example) Hydrogen has a combining capacity of 1; & Oxygen has a combining capacity of 1.
1
2
(write the name of the combining capacity above the atom’s symbol)
H
O
(use the criss-cross method to form subscripts)
H2O
(it takes 2 hydrogen atoms to meet the combining capacity of 1 oxygen atom)
= water
O
o
H
O
Example) Nitrogen and Hydrogen
3
1
N
H
H
NH3
N
H
H
= Ammonia
o
Example) Oxygen gas
2
O
O
O
 Naming Molecular Compounds
o
We use prefixes to with each atom in the molecular compound.
o
The prefix indicates the subscript (number of atoms) for each element.
Prefix
Number
Prefix
Number
monoditritetra-
1
2
3
4
pentahexaheptaocta-
5
6
7
8
o
We NEVER reduce the subscripts in a molecular compound because it could completely
change the actual compound. For example) NO2 is called Nitrogen dioxide and is pare of
smog. However, N2O4 is called Dinitrogen tetroxide, and is used in rocket fuel.

1st step: Look at the subscript for the first element. Add a prefix to the front of
the name of the element.


Do not add the prefix “mono” to the 1st element if the subscript is a “1”.
2nd step: Look at the subscript of the second element. Add a prefix to the front
of the name, and change the end of the element’s name to a suffix of “-ide”.


Some Molecular Compounds have common names:
o
Water (H2O)
o
Methane (CH4)
o
Ammonia (NH3)
o
Hydrogen peroxide (H2O2)
Practice:
Name the following Molecular Compounds
a) C3N4


Practice:
c) SBr2
Give the chemical formula for the following Molecular Compounds
a) Diphosphorus trioxide
b) Methane
c) Selenium dichloride
d) Bromine gas
Practice:
Give the name & chemical formula for the following Molecular Compounds
a) Nitrogen and Oxygen

b) NH3
Practice:
a) Cl2
b) Hydrogen and Oxygen
c) Arsenic and Sulfur
Draw a diagram of the covalent bonds for these Molecular Compounds
b) NH3
c) CH4