Molecular Polarity

Question 1

What role does electronegativity play in determining the polarity of a molecule?

Answer 1

Atoms share electrons to a greater or lesser extent depending on the electronegativity of the elements. Electronegativity is the ability of an atom to attract electrons: the higher its electronegativity, the more strongly an atom attracts shared electrons to itself.

Question 2

For a molecule to be polar, its shape must be (symmetric/asymmetric) so that the dipole moments (cancel out/do not cancel out).

Answer 2

The molecule should be asymmetric so the dipoles do not cancel out.

[an image comparing these traits would be helpful here]

Question 3

How can you determine the polarity of a bond within a molecule?

Answer 3

You can determine the polarity of a bond by looking at the difference in electronegativity between the two atoms involved. If the difference is significant, the bond is considered polar because one atom will attract the shared electrons more strongly, creating a dipole moment.

Question 4

Is carbon dioxide (CO2) a polar or a non-polar molecule and why?

Answer 4

CO2 is a nonpolar molecule. The bonds between carbon and oxygen are polar due to the difference in electronegativity, but the molecule is linear and symmetrical causing the dipole moments of the bonds to cancel each other out.

[an image showing this would be helpful here]

Essentially, molecular polarity is the result of the sum of all the individual bond dipoles within the molecule, which can be canceled out or not depending on the molecule shape (symmetry).

Question 5

Compare the bonds and molecular shape and polarity between a water molecule H2O and a methane molecule CH4.

Answer 5

Bonds: The individual bonds of methane are slightly polar because carbon and hydrogen differ slightly in their electronegativity, whereas, the bonds between oxygen and hydrogen in a water molecule are quite polar.
Shape: the carbon molecule is more symmetrical while the water molecule is asymmetrical.
Polarity: the water molecule is polar (negative partial charge on the O side) while the carbon molecule is non-polar.

[an image comparing these molecules would be helpful here]

Oxygen is one of the most electronegative elements in existence.