Question

Which of the following molecules contain polar covalent bonds? a. carbon monoxide, \(\mathrm{CO}\) b. chlorine, \(\mathrm{Cl}_{2}\) c. iodine monochloride, ICl d. phosphorus, \(\mathrm{P}_{4}\)

Short answer

The molecules containing polar covalent bonds are a. carbon monoxide, \(\mathrm{CO}\), and c. iodine monochloride, ICl.

Step-by-step solution

Understand polar covalent bonds

A polar covalent bond is a type of chemical bond in which the sharing of electrons between atoms is unequal, causing a partial positive charge on one atom and a partial negative charge on the other. This unequal distribution of electrons occurs when there is a significant electronegativity difference between the bonding atoms (usually around 0.5 to 1.7).

Analyze carbon monoxide (CO)

Carbon monoxide is a diatomic molecule consisting of one carbon atom and one oxygen atom. The electronegativity difference between carbon (2.55) and oxygen (3.44) is 0.89. This difference is within the polar covalent range, indicating that CO has a polar covalent bond between the carbon and oxygen atoms.

Analyze chlorine (Cl2)

Chlorine is a diatomic molecule consisting of two chlorine atoms. The electronegativity difference between two identical atoms is zero, meaning that there is equal sharing of electrons and no polarity in the bond. Therefore, Cl2 does not have a polar covalent bond.

Analyze iodine monochloride (ICl)

Iodine monochloride is a diatomic molecule consisting of one iodine atom and one chlorine atom. The electronegativity difference between iodine (2.66) and chlorine (3.16) is 0.50. This difference falls within the polar covalent range, indicating that ICl has a polar covalent bond between the iodine and chlorine atoms.

Analyze phosphorus (P4)

Phosphorus is a tetrahedral molecule consisting of four phosphorus atoms. As with chlorine, the electronegativity difference between identical atoms is zero, indicating equal sharing of electrons and no polarity in the bond. Therefore, P4 does not have polar covalent bonds.

Determine the answer

Based on the analysis of each molecule, we can conclude that carbon monoxide (CO) and iodine monochloride (ICl) contain polar covalent bonds. Therefore, the answer is a. carbon monoxide, \(\mathrm{CO}\), and c. iodine monochloride, ICl.

Key concepts

Electronegativity Difference

The electronegativity difference between atoms is a key factor in determining the type of chemical bond they form. It refers to the ability of an atom to attract electrons in a chemical bond. When two atoms are involved in a chemical bond, their electronegativity values can determine whether the bond is polar, nonpolar, or even ionic.

A significant difference in electronegativity, usually between 0.5 to 1.7, leads to polar covalent bonds. This means electrons are unequally shared between the atoms, creating a partial positive charge on the atom with lower electronegativity and a partial negative charge on the higher electronegativity atom. To remember easily, large differences in electronegativity cause more polar bonds.

• If the difference is between 0 and 0.4, the bond is often considered nonpolar covalent.
• A difference greater than 1.7 typically leads to ionic bonding where electrons are transferred rather than shared equally.

Chemical Bonding

Chemical bonding is the force that holds atoms together, enabling the formation of molecules. Understanding the type of bond between atoms helps predict the properties and behavior of a molecule.

There are several types of chemical bonds, with the main ones being:

• **Ionic Bonds**: Formed when metals transfer electrons to nonmetals, resulting in two oppositely charged ions that attract each other.
• **Covalent Bonds**: Occur when nonmetal atoms share electrons to obtain a full outer shell, stabilizing the molecule.
• **Polar Covalent Bonds**: A subtype of covalent bonds where the electrons are shared unequally due to differences in electronegativity.

In polar covalent bonds, because of unequal sharing of electrons, a dipole moment is created. This can affect how the molecule interacts with others, influencing things like solubility and boiling point.

Molecular Polarity

Molecular polarity is a concept that describes how the charge is distributed across a molecule. It depends on both the polarity of its bonds and its geometric shape.

For a molecule to be polar, it needs:

• **Polar Bonds**: As mentioned, these arise from differences in electronegativity.
• **Asymmetric Shape**: Even if a molecule has polar bonds, it can be nonpolar overall if the geometry is symmetrical, causing dipole moments to cancel out.
  Familiar examples include carbon dioxide (\( \text{CO}_2\) ) which is linear and nonpolar despite polar bonds.
  

Understanding molecular polarity is crucial as it influences molecular interactions, such as solubility in water and biological interactions in cells. Thus, examining both individual bond polarity and molecular shape offers insights into physical and chemical properties.