Question

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

Short answer

a. Polar Covalent; b. Ionic; c. Polar Covalent; d. Nonpolar Covalent; e. Polar Covalent; f. Polar Covalent

Step-by-step solution

Understand the types of bonds

There are three main types of chemical bonds: ionic, polar covalent, and nonpolar covalent. Ionic bonds occur between a metal and a non-metal, involving the transfer of electrons. Polar covalent bonds occur between two non-metals where electrons are shared unequally. Nonpolar covalent bonds occur between two non-metals where electrons are shared equally.

Compare electronegativities

The periodic table can be used to find the electronegativity values for each element. The differences in electronegativity will help determine the bond type:- Nonpolar Covalent: Electronegativity difference < 0.5- Polar Covalent: Electronegativity difference between 0.5 and 1.7- Ionic: Electronegativity difference > 1.7

Analyze each bond

a. \(\mathrm{Si}-\mathrm{Br}\): Electronegativity of Si = 1.90, Br = 2.96, Difference = 1.06. \(\text{Polar Covalent}\)b. \(\mathrm{Li}-\mathrm{F}\): Electronegativity of Li = 0.98, F = 3.98, Difference = 3.00. \(\text{Ionic}\)c. \(\mathrm{Br}-\mathrm{F}\): Electronegativity of Br = 2.96, F = 3.98, Difference = 1.02. \(\text{Polar Covalent}\)d. I - I: Electronegativity of I = 2.66, Difference = 0.00. \(\text{Nonpolar Covalent}\)e. \(\mathrm{N}-\mathrm{P}\): Electronegativity of N = 3.04, P = 2.19, Difference = 0.85. \(\text{Polar Covalent}\)f. \(\mathrm{C}-\mathrm{O}\): Electronegativity of C = 2.55, O = 3.44, Difference = 0.89. \(\text{Polar Covalent}\)

Key concepts

Ionic Bonds

Ionic bonds are one of the primary types of chemical bonds.
They form when there is a large electronegativity difference (> 1.7) between the bonded atoms.
This usually occurs between a metal and a non-metal.
The metal loses one or more electrons, becoming a positively charged ion (cation).
The non-metal, in contrast, gains these electrons, becoming a negatively charged ion (anion).
Due to the opposite charges, these ions attract each other, forming a strong ionic bond.

For example, in the bond \(\text{Li-F}\), Lithium (metal) loses an electron to Fluorine (non-metal), forming an ionic bond because the electronegativity difference (3.00) is greater than 1.7.
This results in a clear electron transfer creating ions with opposite charges which attract each other strongly.

Polar Covalent Bonds

Polar covalent bonds occur between two non-metals where electrons are shared unequally.
These arise with moderate electronegativity differences (0.5 - 1.7) between the atoms.
One atom attracts the shared electrons more strongly, causing a partial positive charge on one atom and a partial negative charge on the other.
Because of this unequal sharing, polar covalent bonds often create dipoles.

For instance, in the bond \(\text{Si-Br}\), Silicon and Bromine share electrons but not equally.
The electronegativity of Br (2.96) is higher than Si (1.90), resulting in Bromine pulling the shared electrons closer.
The difference (1.06) is within the polar covalent range, resulting in a bond where Br has a partial negative charge and Si a partial positive charge.

Nonpolar Covalent Bonds

Nonpolar covalent bonds are formed when two non-metals share electrons equally.
This happens when the electronegativity difference between the atoms is less than 0.5.
In these bonds, the electron distribution between the two atoms is perfectly balanced.
There are no partial charges in nonpolar covalent bonds.

A good example is the \(\text{I-I}\) bond.
Both iodine atoms have the same electronegativity (2.66).
So, the electrons are shared equally between them.
This equal sharing results in a nonpolar covalent bond with no partial charges.

Electronegativity Differences

Electronegativity is a measure of an atom's ability to attract shared electrons.
The difference in electronegativity between atoms in a bond often determines the bond type.

• Nonpolar covalent bonds: Electronegativity difference < 0.5
• Polar covalent bonds: Electronegativity difference between 0.5 and 1.7
• Ionic bonds: Electronegativity difference > 1.7

For example, in the bond \(\text{C-O}\), Carbon has an electronegativity of 2.55 and Oxygen has 3.44, leading to a difference of 0.89.
This falls into the polar covalent range.
Electrons are shared unequally, with Oxygen having a partial negative charge because it attracts the electrons more strongly than Carbon.