Polarity (H Chem A)

Bond polarity and Molecular polarity

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Multiple Select

Use the "two atoms" tab of the simulation. How can you make a bond polar?

• give both atoms high electronegativities

• Give both atoms low electronegativities

• Give atom "A" a high electronegativity and atom "B" a low electronegativity

• Give atom "B" a high electronegativity and atom "A" a low electronegativity

If two atoms have the same electronegativities, they will share the electrons equally.

(Like a game of tug-o-war with your twin)

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Equal sharing

Covalent bonds result from sharing electrons. But this sharing isn't always equal. If the atoms have different electronegativity values, this will result in the electrons being pulled more toward the atom with a higher electronegativity.


This results in a bond dipole.

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Unequal sharing of electrons

Multiple Select

Using the simulation, when a polar bond exists, which atom has a partial negative charge?

• the more electronegative atom

• the less electronegative atom

• the atom that the arrow points to

• the atom at the back of the arrow (with the + sign)

Multiple Select

Using the simulation, when a polar bond exists, which atom has more electron density?

• the more electronegative atom

• the less electronegative atom

• the atom that the arrow points to

• the atom at the back of the arrow (with the + sign)

Multiple Choice

What happens to the bond character when you make the electronegativities as different as possible?

• It becomes nonpolar

• it becomes ionic

• it becomes polar

• It becomes covalent

The greater the difference in electronegativity, the more polar is the bond.

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Polar Covalent bonds

• Electronegativity is the ability of atoms in a molecule to attract electrons to themselves.

• On the periodic chart, electronegativity increases as you go…

  • …from left to right across a row.

  • …from the bottom to the top of a column.

​When Cl bonds with Cl, they pull equally on the electrons, so they have equal electron density around each atom and form a nonpolar bond.

When Cl and H form a bond, Cl is more electronegative and therefore pulls the electrons more toward itself.

When Cl and Na form a bond, the electronegativity difference is so large that Na gives electrons to Cl

Types of bonds

Multiple Select

Now use the "3 atoms" tab. What happens when you move atom "A" to be opposite atom "C"? (180^o away) but you change nothing else?

• the bond dipoles cancel

• the molecular dipole goes away

• the molecular becomes polar

• the bond dipoles add up to make a large molecular dipole

Multiple Select

Now use the "3 atoms" tab. Which shape(s) result in a polar molecule (do not change the electronegativity values yet)?

• bent

• linear

Multiple Choice

Can you make a linear molecule polar?

• No, the dipoles always cancel.

• Yes, if you change the electronegativity values so that the bond dipoles don't cancel

• Yes, if you make the bond dipoles cancel

• No, linear molecules can't have bond dipoles.

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Now let's look at real molecules. Water is polar, but CO₂ is not. Why?

• water is bent and the dipoles do not cancel

• CO₂ is linear and the dipoles do not cancel

• CO₂ is linear and the dipoles do cancel

• water is bent and the dipoles do cancel

Multiple Choice

BH₃ is not polar. Why is NH₃?

• It's dipoles don't cancel b/c it is trigonal pyramidal

• It's dipoles don't cancel b/c it is trigonal planar

• It's dipoles don't cancel b/c they are different sizes

• It's dipoles don't cancel b/c it is bent

Multiple Choice

Methane is not polar, but fluoromethane is. Why?

• Although they are both tetrahedral, fluoromethane has an "F" atom with results in an unequal sharing of electrons

• Methane is tetrahedral, but fluoromethane is trigonal pyramidal so the dipoles don't cancel.

• Methane is tetrahedral, but fluoromethane is see-saw so the dipoles don't cancel.

• Methane is tetrahedral so the dipoles cancel, but fluoromethane is bent so the dipoles don't cancel.

Multiple Choice

Why isn't tetrafluoromethane polar?

• It has no polar bonds

• It's dipoles cancel

• It has polar bonds but the dipoles do not cancel.

• It is symmetric so its dipoles do not cancel.

Multiple Choice

Would you expect HCl to be polar?

• yes

• no

Multiple Select

To identify a polar molecule, you should look for . . .

• different types of atoms that have different electronegativities

• a lack of symmetry in the shape of the molecule

• a lone pair on the central atom b/c this could indicate a lack of symmetry

• Different types of atoms only (the shape of the molecule doesn't matter)

Multiple Choice

C and H have the same electronegativity value, therefore, molecules that contain only C and H

• contain polar bonds

• contain polar bonds but are not polar molecules

• do not contain polar bonds

• do not contain polar bonds and cannot be polar molecules.