How to Determine the Polarity of a Molecule
Write the symbols for all atoms in the molecule., Find the central atom., Add all of the bonds., Include unbound electrons., Look for dipoles.
Step-by-Step Guide
-
Step 1: Write the symbols for all atoms in the molecule.
Atomic symbols for atoms can be found on the periodic table.
These symbols are used to represent each atom in a Lewis dot structure.
Be sure not to mix up the symbols, as this would cause confusion.For example, if you are looking at a water molecule, you would write out O, H, and H. -
Step 2: Find the central atom.
The central atom is the atom that all (or at least most) of the other atoms is bonded to.
Those atoms may or may not be bonded to each other as well.
As a rule of thumb, central atoms are usually atoms with low electronegativity.The water molecule breaks this general trend since the oxygen atom (the most electronegative atom in the molecule) is the center atom.
Carbon dioxide is an example of a molecule that follows the trend of center atoms being less electronegative. , Use the octet rule to determine the number and type of bonds present.
Each atom’svalence shell should contain eight electrons for the molecule to be stable.
Some atoms may be double or triple bonded to achieve this.You should add a single bond from the oxygen to both hydrogens.
The hydrogens are not bonded to each other. , While most electrons are used in bonding, some atoms have a set of non bonding electrons.
These electrons should also be included in the Lewis structure, as they are very important when determining polarity.
Represent all electrons (bonded and unbonded) with dots around their respective atoms.Oxygen has two lone pair electrons.
This means they are not used for bonding, but stay attached to the oxygen. , A dipole exists when electrons are unevenly distributed from one side of the molecule to the other.
If this is present, then the molecule is polar.
If the distribution looks even, the molecule is nonpolar.Since electrons are more attracted to oxygen than hydrogen, they tend to congregate on that end of the molecule.
That gives the oxygen a negative charge and the hydrogens a positive charge, creating a dipole.
Thus, water is polar. -
Step 3: Add all of the bonds.
-
Step 4: Include unbound electrons.
-
Step 5: Look for dipoles.
Detailed Guide
Atomic symbols for atoms can be found on the periodic table.
These symbols are used to represent each atom in a Lewis dot structure.
Be sure not to mix up the symbols, as this would cause confusion.For example, if you are looking at a water molecule, you would write out O, H, and H.
The central atom is the atom that all (or at least most) of the other atoms is bonded to.
Those atoms may or may not be bonded to each other as well.
As a rule of thumb, central atoms are usually atoms with low electronegativity.The water molecule breaks this general trend since the oxygen atom (the most electronegative atom in the molecule) is the center atom.
Carbon dioxide is an example of a molecule that follows the trend of center atoms being less electronegative. , Use the octet rule to determine the number and type of bonds present.
Each atom’svalence shell should contain eight electrons for the molecule to be stable.
Some atoms may be double or triple bonded to achieve this.You should add a single bond from the oxygen to both hydrogens.
The hydrogens are not bonded to each other. , While most electrons are used in bonding, some atoms have a set of non bonding electrons.
These electrons should also be included in the Lewis structure, as they are very important when determining polarity.
Represent all electrons (bonded and unbonded) with dots around their respective atoms.Oxygen has two lone pair electrons.
This means they are not used for bonding, but stay attached to the oxygen. , A dipole exists when electrons are unevenly distributed from one side of the molecule to the other.
If this is present, then the molecule is polar.
If the distribution looks even, the molecule is nonpolar.Since electrons are more attracted to oxygen than hydrogen, they tend to congregate on that end of the molecule.
That gives the oxygen a negative charge and the hydrogens a positive charge, creating a dipole.
Thus, water is polar.
About the Author
Richard Wilson
Writer and educator with a focus on practical organization knowledge.
Rate This Guide
How helpful was this guide? Click to rate: