Relationship Between Formal Charge and Partial Charge Practice Worksheet Answer Key

Relationship Between Formal Charge and Partial Charge Practice Worksheet Answer Key:

For each pair of molecules given, draw any dipoles or partial charges that are present. Compare the two molecules and explain any differences in dipoles and/or partial charges. Consider factors such as electronegativity and formal charges in your explanation.

1.

In both molecules there are dipoles towards the oxygen atoms, away from the atoms they’re bonded to. This is because oxygen is a FON element, so it will always create polar bonds unless it is bonded to itself.

However, the dipoles towards the formally positive oxygen are larger than the dipoles towards the neutral oxygen. This is because oxygen will always get itself to a partially negative state due to its extremely high electronegativity. Therefore, the formally positive oxygen has to pull harder to delocalize more electron density away from the atoms it is bonded to. This is due to the formally positive oxygen starting in an electron deficient state. The formally neutral oxygen does not need to delocalize as much electron density to become partially negative.

Due to the dipoles towards the formally positive oxygen being larger, the hydrogens and carbon it is bonded to will be more partially positive than the hydrogen and carbon bonded to the formally neutral oxygen.

2.

In both molecules there are dipoles towards the oxygen atoms, away from the atoms they’re bonded to. This is because oxygen is a FON element, so it will always create polar bonds unless it is bonded to itself.

However, the dipoles towards the formally neutral oxygen are larger than the dipole towards the formally negative oxygen. This is because oxygen will always get itself to a partially negative state due to its extremely high electronegativity. Therefore, the formally neutral oxygen has to pull harder to delocalize more electron density away from the atoms it is bonded to. This is due to the formally neutral oxygen starting with less electron density than the formally negative oxygen. The formally negative oxygen does not need to delocalize as much electron density to obtain its partially negative state.

Due to the dipoles towards the formally neutral oxygen being larger, the hydrogens it is bonded to will be more partially positive than the hydrogen bonded to the formally negative oxygen.

3.

In both molecules, there are dipoles towards the hydrogen atoms, away from the aluminum they’re bonded to. This is because an Al-H bond is polar due to hydrogen being significantly more electronegative than aluminum. Note that aluminum is a metal, and hydrogen is a non-metal. All metal + non-metal bonds are polar.

The dipoles towards the hydrogens in both examples are the same size. This is because the hydrogens all start formally neutral in both molecules and will therefore pull the same amount of electron density towards themselves.

The aluminum in the AlH3 molecule ends with a larger partial positive charge than the aluminum in AlH4- does. This is due to the aluminum in AlH4- starting formally negative, meaning it has an excess of electron density. Therefore, when the hydrogens delocalize electron density away from the formally negative aluminum, it has some density to give before it starts becoming positive. The formally neutral aluminum in AlH3 does not start with any excess electron density, so it ends with a larger partial positive charge.

4.

In the formally neutral molecule, there are no dipoles or partial charges. Every bond present is C-C or C-H, which are both non-polar bonds.

In the molecule with the formally positive carbon, there are dipoles towards the formally positive carbon due to that carbon being electron deficient. It pulls electron density in from the surrounding methyl groups to make up for its deficiency. This causes partial positive charges on the surrounding carbons.

The formally positive carbon also has a partial positive charge. This is due to carbon having a relatively low electronegativity value. Carbon does not want any excess electron density, so it does not pull hard enough to become formally negative. However, this fact means that it also does not pull hard enough to completely get rid of its electron deficiency, which is why it ends with a partial positive charge.

5.

In both molecules there are dipoles towards the oxygen atoms, away from the atoms they’re bonded to. This is because oxygen is a FON element, so it will always create polar bonds unless it is bonded to itself.

However, the dipoles towards the formally positive oxygen are larger than the dipoles towards the neutral oxygen. This is because oxygen will always get itself to a partially negative state due to its extremely high electronegativity. Therefore, the formally positive oxygen has to pull harder to delocalize more electron density away from the atoms it is bonded to. This is due to the formally positive oxygen starting in an electron deficient state. The formally neutral oxygen does not need to delocalize as much electron density to become partially negative.

Due to the dipoles towards the formally positive oxygen being larger, the hydrogen and carbon it is bonded to will be more partially positive than the hydrogen and carbon bonded to the formally neutral oxygen.

6.

In both molecules there are dipoles towards the oxygen atoms, away from the atoms they’re bonded to. This is because oxygen is a FON element, so it will always create polar bonds unless it is bonded to itself.

However, the dipoles towards the formally positive oxygen are larger than the dipoles towards the neutral oxygen. This is because oxygen will always get itself to a partially negative state due to its extremely high electronegativity. Therefore, the formally positive oxygen has to pull harder to delocalize more electron density away from the atoms it is bonded to. This is due to the formally positive oxygen starting in an electron deficient state. The formally neutral oxygen does not need to delocalize as much electron density to become partially negative.

Due to the dipoles towards the formally positive oxygen being larger, the hydrogens and carbon it is bonded to will be more partially positive than the hydrogen and carbon bonded to the formally neutral oxygen.

7.

In both molecules there are dipoles towards the nitrogen atoms, away from the atoms they’re bonded to. This is because nitrogen is a FON element, so it will always create polar bonds unless it is bonded to itself.

However, the dipoles towards the formally positive nitrogen are larger than the dipoles towards the neutral nitrogen. This is because nitrogen will always get itself to a partially negative state due to its extremely high electronegativity. Therefore, the formally positive nitrogen has to pull harder to delocalize more electron density away from the atoms it is bonded to. This is due to the formally positive nitrogen starting in an electron deficient state. The formally neutral nitrogen does not need to delocalize as much electron density to become partially negative.

Due to the dipoles towards the formally positive nitrogen being larger, the hydrogens and carbons it is bonded to will be more partially positive than the hydrogen and carbons bonded to the formally neutral oxygen.

8.

There are dipoles towards both the oxygen and nitrogen atoms, away from the atoms they’re bonded to. This is because oxygen and nitrogen are both FON elements, so they will always create polar bonds unless they are bonded to themselves.

Even though the nitrogen is electron deficient (shown via the formal positive charge), the dipoles towards the formally neutral oxygen are larger. This occurs because oxygen is significantly more electronegative than nitrogen. Because oxygen is significantly more electronegative than nitrogen, it will delocalize more electron density to end up in a larger partial negative state.

Due to the dipoles towards the formally neutral oxygen being larger, the hydrogen and carbon it is bonded to will be more partially positive than the hydrogens and carbon bonded to the formally negative nitrogen.

9.

In both molecules, there are dipoles away from the metal atoms bonded to the carbon atoms. This is because both Mg-C and Li-C bonds are polar due to carbon being significantly more electronegative than Mg and Li. Note that both magnesium and lithium are metals, and carbon is a non-metal. All metal + non-metal bonds are polar.

The dipole towards carbon away from lithium is larger than the dipole towards carbon away from magnesium. This is because lithium is less electronegative than magnesium. This difference in electronegativity creates a bond between carbon and lithium that is more polar than a bond between carbon and magnesium.

Due to the dipole towards carbon away from lithium being larger, the partial negative charge on that carbon is larger than the partial negative charge on the carbon bonded to magnesium. The partial positive charge on lithium is also larger than the partial positive charge on magnesium. This is because lithium is less electronegative than magnesium, so its affinity for electron density is lower.

10.

In both molecules there are dipoles towards the nitrogen atoms, away from the atoms they’re bonded to. This is because nitrogen is a FON element, so it will always create polar bonds unless it is bonded to itself.

However, the dipoles towards the formally positive nitrogen are larger than the dipoles towards the neutral nitrogen. This is because nitrogen will always get itself to a partially negative state due to its extremely high electronegativity. Therefore, the formally positive nitrogen has to pull harder to delocalize more electron density away from the atoms it is bonded to. This is due to the formally positive nitrogen starting in an electron deficient state. The formally neutral nitrogen does not need to delocalize as much electron density to become partially negative.

Due to the dipoles towards the formally positive nitrogen being larger, the hydrogens and carbon it is bonded to will be more partially positive than the hydrogen and carbons bonded to the formally neutral nitrogen.