Question

Predict whether each of the following bonds is ionic, polar covalent, or nonpolar covalent: a. \(\mathrm{Si}-\mathrm{O}\) b. \(\mathrm{K}-\mathrm{Cl}\) c. \(\mathrm{S}-\mathrm{F}\) d. \(\mathrm{P}-\mathrm{Br}\) e. \(\mathrm{Li}-\mathrm{O}\) f. \(\mathrm{N}-\mathrm{S}\)

Short answer

a. Polar covalentb. Ionicc. Polar covalentd. Polar covalente. Ionicf. Polar covalent

Step-by-step solution

Understand Electronegativity Differences

Electronegativity differences between atoms help determine bond type. If the difference is greater than 2.0, the bond is ionic. If it is between 0.4 and 2.0, the bond is polar covalent. If it is less than 0.4, the bond is nonpolar covalent.

Determine Electronegativity Values

Find the electronegativity values for all atoms involved. For example, Silicon (Si) is 1.90, Oxygen (O) is 3.44, Potassium (K) is 0.82, Chlorine (Cl) is 3.16, Sulfur (S) is 2.58, Fluorine (F) is 3.98, Phosphorus (P) is 2.19, Bromine (Br) is 2.96, Lithium (Li) is 0.98, and Nitrogen (N) is 3.04.

Calculate Electronegativity Differences

Calculate the differences: a. \(\text{Si-O: } 3.44 - 1.90 = 1.54\) b. \(\text{K-Cl: } 3.16 - 0.82 = 2.34\) c. \(\text{S-F: } 3.98 - 2.58 = 1.40\) d. \(\text{P-Br: } 2.96 - 2.19 = 0.77\) e. \(\text{Li-O: } 3.44 - 0.98 = 2.46\) f. \(\text{N-S: } 2.58 - 3.04 = 0.46\) (note that the absolute value is taken)

Classify Each Bond

Using the differences calculated: a. Si-O: 1.54 (Polar covalent) b. K-Cl: 2.34 (Ionic) c. S-F: 1.40 (Polar covalent) d. P-Br: 0.77 (Polar covalent) e. Li-O: 2.46 (Ionic) f. N-S: 0.46 (Polar covalent)

Key concepts

Electronegativity

Electronegativity is a measure of an atom's ability to attract and hold onto electrons. It's a fundamental concept in chemistry that helps us understand bond formation. Different elements have different electronegativity values. These values can be found on electronegativity charts. For instance:

• Silicon (Si): 1.90
• Oxygen (O): 3.44
• Potassium (K): 0.82

The difference in electronegativity between two atoms helps predict the type of bond they will form. The larger the difference, the more 'ionic' the bond, and the smaller the difference, the more 'covalent'.

Ionic Bonds

Ionic bonds occur when the electronegativity difference between two atoms is greater than 2.0. In an ionic bond, one atom donates its electron to the other, resulting in the formation of ions. These ions have opposite charges and attract each other to form a bond. For example, in the bond between potassium (K) and chlorine (Cl):

• Electronegativity of K: 0.82
• Electronegativity of Cl: 3.16
• Difference: 3.16 - 0.82 = 2.34

Since the difference is more than 2.0, K-Cl is an ionic bond. Here, potassium loses an electron to become K⁺, and chlorine gains an electron to become Cl⁻.

Polar Covalent Bonds

Polar covalent bonds form when the electronegativity difference between two atoms ranges from 0.4 to 2.0. In these bonds, the electrons are shared unequally between the atoms, leading to a partial charge on each atom.
For example, in the bond between silicon (Si) and oxygen (O):

• Electronegativity of Si: 1.90
• Electronegativity of O: 3.44
• Difference: 3.44 - 1.90 = 1.54

Since the difference is between 0.4 and 2.0, Si-O is a polar covalent bond. This means that oxygen, being more electronegative, will attract the shared electrons more strongly, leading to a slight negative charge on oxygen and a slight positive charge on silicon.

Nonpolar Covalent Bonds

Nonpolar covalent bonds occur when the electronegativity difference between two atoms is less than 0.4. Here, the electrons are shared equally between the atoms, and there is no charge separation.
For example, in a bond where the atoms have similar electronegativity values, such as carbon-hydrogen (C-H), if we were considering them:

• Electronegativity of C: ~2.55
• Electronegativity of H: ~2.20
• Difference: 2.55 - 2.20 = 0.35

Since the difference is less than 0.4, C-H would be a nonpolar covalent bond. In real textbook problems, a direct example like N-S, found in the original exercise, shows 0.46 (slightly greater than 0.4), making it not purely nonpolar but illustrative enough to show closeness to nonpolarity.