Question

Which of the following molecules contain polar covalent bonds? a. phosphorus, \(\mathrm{P}_{4}\) b. oxygen, \(\mathrm{O}_{2}\) c. ozone, \(\mathrm{O}_{3}\) d. hydrogen fluoride, HF

Short answer

Only hydrogen fluoride, HF (option d), contains polar covalent bonds due to the significant difference in electronegativity between hydrogen (2.1) and fluorine (3.98). The other molecules consist of non-polar covalent bonds because of equal electronegativity values of the atoms involved in bonding.

Step-by-step solution

Analyze phosphorus, \(\mathrm{P}_4\)

In a \(\mathrm{P}_4\) molecule, there are four phosphorus atoms covalently bonded to form a tetrahedron. Since all the atoms involved in the bonding are the same element, there will be no difference in electronegativity values and therefore no polar covalent bonds. The bonds in this molecule are non-polar covalent bonds.

Analyze oxygen, \(\mathrm{O}_2\)

In an \(\mathrm{O}_2\) molecule, two oxygen atoms are covalently double bonded to each other. As both atoms are the same element, the electronegativity values are equal, and there is no uneven distribution of electron density. The bond in this molecule is non-polar covalent.

Analyze ozone, \(\mathrm{O}_3\)

Ozone, \(\mathrm{O}_3\), has a resonance structure where the oxygen atoms have partial double and partial single bond character. Importantly, all bonding is still between oxygen atoms which have the same electronegativity values. As a result, there is no significant difference in electronegativity between the bonded atoms, and the bonds in ozone are non-polar covalent bonds.

Analyze hydrogen fluoride, HF

In an HF molecule, a hydrogen atom is covalently bonded to a fluorine atom. Hydrogen has an electronegativity value of 2.1, while fluorine has a value of 3.98. There is a significant difference in electronegativity between the two atoms (a difference greater than 0.5 is often considered as polar), leading to an uneven distribution of electron density and the formation of a dipole within the bond. Therefore, the bond in hydrogen fluoride is a polar covalent bond.

Conclusion

Based on our analysis of the molecules, only hydrogen fluoride (option d) contains polar covalent bonds. The other molecules (phosphorus, oxygen, and ozone) consist of non-polar covalent bonds due to the same electronegativity values of the atoms involved in the bonding.

Key concepts

Electronegativity

Electronegativity is a key element in understanding why some bonds become polar, while others remain non-polar. It is a measure of how strongly an atom can attract electrons in a bond towards itself. Each element has a characteristic electronegativity value, with fluorine being the most electronegative element. In a covalent bond, if there is a significant difference in the electronegativity values of the atoms involved, the electrons will spend more time closer to the more electronegative atom. This creates a polar covalent bond, where one end of the bond is slightly negative, and the other is slightly positive.
* For instance, in the hydrogen fluoride (HF) molecule, fluorine has a much higher electronegativity compared to hydrogen. This results in a greater "pull" on the shared electrons, creating a polar covalent bond.
* However, if the atoms have the same or very similar electronegativity values, the electrons are shared equally, resulting in a non-polar covalent bond.

Understanding electronegativity is crucial for predicting the properties and behavior of molecules in chemical reactions and in different environments.

Non-polar Covalent Bonds

Non-polar covalent bonds occur when atoms with equal or very similar electronegativity values share electrons evenly. This means there is no permanent charge difference at either end of the bond, making it non-polar. These bonds often form between identical atoms or atoms of similar electronegativity.
* A classic example is the bond in a diatomic nitrogen ( _2) or oxygen ( _2) molecule, where the electrons are distributed evenly.
* Molecules formed with non-polar covalent bonds, like phosphorus ( _4) or ozone ( _3), do not have partial charges, making them less reactive in polar environments.

However, understand that even in molecules with non-polar bonds, factors like molecular shape can still create polar molecules. It's the distribution and the distance of these bonds within the molecule that contributes to the overall molecular polarity.

Molecular Analysis

Molecular analysis involves examining the types of bonds and the structure of a molecule to understand its properties. This is done by identifying the types of atoms involved, the differences in electronegativity, and the overall molecular geometry.
* For instance, when analyzing hydrogen fluoride (HF), we note the significant electronegativity difference leading to a polar covalent bond. This information allows us to predict HF's behavior in various chemical processes, such as its solubility in water or its role as a strong acid.
* Conversely, in a molecule like phosphorus ( _4) or oxygen ( _2), the identical atoms ensure an equal sharing of electrons, resulting in non-polar behavior.

Molecular analysis not only allows chemists to determine the bond types but also helps in predicting physical properties such as boiling and melting points, solubility, and reactivity. This forms the foundation for understanding molecular interactions in chemistry and biology.