Question

Which compounds have nonpolar covalent bonds, which have polar covalent bonds, and which have ions? (a) LiF (b) \(\mathrm{CH}_{3} \mathrm{~F}\) (c) \(\mathrm{MgCl}_{2}\) (d) \(\mathrm{HCl}\)

Short answer

Question: Categorize the following compounds as having nonpolar covalent bonds, polar covalent bonds, or ionic bonds: (a) LiF, (b) CH3F, (c) MgCl2, (d) HCl. Answer: (a) LiF has ionic bonds, (b) CH3F has both nonpolar and polar covalent bonds, (c) MgCl2 has ionic bonds, and (d) HCl has polar covalent bonds.

Step-by-step solution

(a) LiF

The electronegativity difference between lithium (Li) and fluorine (F) is 3.98 - 0.98 = 3.0, which is greater than 1.7. Therefore, LiF has ionic bonds.

(b) \(\mathrm{CH}_{3} \mathrm{~F}\)

In this compound, we have two types of bonds: C-H and C-F. For the C-H bond, the electronegativity difference is 2.55 - 2.20 = 0.35, which is less than 0.4, so it is considered nonpolar covalent. For the C-F bond, the electronegativity difference is 3.98 - 2.55 = 1.43, which is between 0.4 and 1.7, so it is considered polar covalent. Overall, \(\mathrm{CH}_{3} \mathrm{~F}\) has both nonpolar and polar covalent bonds.

(c) \(\mathrm{MgCl}_{2}\)

The electronegativity difference between magnesium (Mg) and chlorine (Cl) is 3.16 - 1.31 = 1.85, which is greater than 1.7. Therefore, \(\mathrm{MgCl}_{2}\) has ionic bonds.

(d) \(\mathrm{HCl}\)

The electronegativity difference between hydrogen (H) and chlorine (Cl) is 3.16 - 2.20 = 0.96, which is between 0.4 and 1.7. Therefore, \(\mathrm{HCl}\) has polar covalent bonds.

Key concepts

Nonpolar Covalent Bonds

Nonpolar covalent bonds are formed when two atoms share electrons equally. This typically happens between atoms that have very similar electron attraction abilities, termed as electronegativity. When the electronegativity difference between the two atoms is very small, specifically less than 0.4, the electrons are shared almost equally. This results in a nonpolar covalent bond. An example is the bond between carbon and hydrogen in \({\mathrm{CH}_{3}{\mathrm{~F}}}\), where the difference is 0.35. Such bonds do not possess a dipole moment, meaning there isn't a region of significant positive or negative charge in the bond.

Polar Covalent Bonds

In polar covalent bonds, electrons are shared unevenly between atoms due to differences in electronegativity. When the disparity in electronegativity values ranges from 0.4 to 1.7, the electrons of the bond are pulled closer to the more electronegative atom. This causes one end of the bond to have a slight negative charge while the other gets a slight positive charge, thereby creating a dipole. \({\mathrm{HCl}}\) is an example of a molecule with polar covalent bonds. Here, chlorine is more electronegative than hydrogen, resulting in a shared bond with a dipole moment.

Ionic Bonds

Ionic bonds occur when the electronegativity difference between two atoms exceeds 1.7. In such cases, the more electronegative atom attracts electrons away from the less electronegative atom, resulting in the formation of ions. These ions are oppositely charged and therefore attract each other, creating a strong ionic bond. For instance, \({\mathrm{LiF}}\) and \({\mathrm{MgCl}_{2}}\) are compounds that exhibit ionic bonding. Lithium and magnesium transfer electrons to fluorine and chlorine respectively, leading to their oppositely charged ions.

Electronegativity

Electronegativity is a measure of how strongly an atom attracts bonding electrons to itself. It is a crucial factor in determining the type of bond that will form between two atoms. Generally, higher electronegativity means stronger attraction to electrons. The Pauling scale is often used to quantify electronegativity. Fluorine is known to have the highest electronegativity value, which is why it often participates in forming polar covalent and ionic bonds. Understanding the concept of electronegativity aids in predicting and explaining the nature of chemical bonds in compounds.

Bond Type Determination

The process of determining the type of bond that will form between atoms primarily involves calculating the difference in their electronegativities.

• If the difference is less than 0.4, the bond is likely nonpolar covalent.
• If the difference is between 0.4 and 1.7, it results in a polar covalent bond.
• An electronegativity difference greater than 1.7 typically indicates an ionic bond.

For example, in the molecule of \({\mathrm{HCl}}\), calculating the difference in electronegativity between hydrogen and chlorine results in 0.96, classifying it as a polar covalent bond. This systematic approach allows chemists to predict bonding properties of compounds efficiently.