Problem 141 - Chemistry An Atoms First Approach

Question

Classify the bonding in each of the following molecules as ionic, polar covalent, or nonpolar covalent. a. \(\mathrm{H}_{2}\) b. \(K_{3} P\) c. Nal d. \(\mathrm{SO}_{2}\) e. HF f. \(\mathrm{CCl}_{4}\) g. \(\mathrm{CF}_{4}\) \(\mathbf{h} . \mathbf{K}_{2} \mathbf{S}\)

Step-by-Step Solution

Answer

a. \(\mathrm{H}_{2}\): Nonpolar covalent b. \(K_{3}P\): Ionic c. NaI: Ionic d. \(\mathrm{SO}_{2}\): Polar covalent e. HF: Ionic f. \(\mathrm{CCl}_{4}\): Polar covalent g. \(\mathrm{CF}_{4}\): Polar covalent h. \(K_{2}S\): Ionic

Step 1: Deducing the electronegativity difference

For each molecule, find the electronegativity difference using a table of electronegativity values. a. \(\mathrm{H}_{2}\): Electronegativity of H = 2.20 (both atoms) Difference = \(|2.20 - 2.20|\) = 0.00 b. \(K_{3}P\): Electronegativity of K = 0.82 Electronegativity of P = 2.19 Difference = \(|0.82 - 2.19|\) = 1.37 c. NaI: Electronegativity of Na = 0.93 Electronegativity of I = 2.66 Difference = \(|0.93 - 2.66|\) = 1.73 d. \(\mathrm{SO}_{2}\): Electronegativity of S = 2.58 Electronegativity of O = 3.44 Difference = \(|2.58 - 3.44|\) = 0.86 e. HF: Electronegativity of H = 2.20 Electronegativity of F = 3.98 Difference = \(|2.20 - 3.98|\) = 1.78 f. \(\mathrm{CCl}_{4}\): Electronegativity of C = 2.55 Electronegativity of Cl = 3.16 Difference = \(|2.55 - 3.16|\) = 0.61 g. \(\mathrm{CF}_{4}\): Electronegativity of C = 2.55 Electronegativity of F = 3.98 Difference = \(|2.55 - 3.98|\) = 1.43 h. \(K_{2}S\): Electronegativity of K = 0.82 Electronegativity of S = 2.58 Difference = \(|0.82 - 2.58|\) = 1.76

Step 2: Classifying the bonds

Using the electronegativity difference, classify each bond as ionic, polar covalent, or nonpolar covalent: a. \(\mathrm{H}_{2}\): Nonpolar covalent (difference = 0.00) b. \(K_{3}P\): Ionic (difference = 1.37, but the bond is between a metal and a non-metal) c. NaI: Ionic (difference = 1.73) d. \(\mathrm{SO}_{2}\): Polar covalent (difference = 0.86) e. HF: Ionic (difference = 1.78) f. \(\mathrm{CCl}_{4}\): Polar covalent (difference = 0.61) g. \(\mathrm{CF}_{4}\): Polar covalent (difference = 1.43) h. \(K_{2}S\): Ionic (difference = 1.76)

Key Concepts

Electronegativity Difference

Electronegativity is a chemical property that describes an atom's ability to attract shared electrons in a molecule. The electronegativity difference between two bonding atoms plays a crucial role in determining the type of bond they form.
The greater the difference in electronegativity, the more polar the bond is likely to be. Here’s a quick guide to understanding the classification based on electronegativity difference:

• If the difference is less than 0.5, the bond is generally considered nonpolar covalent. In these bonds, electrons are shared almost equally between the two atoms.
• If the difference is between 0.5 and 1.7, the bond is usually considered polar covalent, meaning electrons are shared unequally, resulting in partial charges on the atoms.
• If the difference is greater than 1.7, the bond is typically ionic. In ionic bonds, one atom donates electrons to another, leading to the formation of positively and negatively charged ions.

Understanding electronegativity helps you predict how atoms will interact and bind, which is pivotal in studying chemical reactions and properties.

Ionic Bonds

Ionic bonds occur when electrons are transferred from one atom to another, creating ions. These are generally formed between metals and non-metals.
For instance:

• Potassium (K) and sulfur (S) in K₂S form an ionic bond as potassium loses electrons to become a positively charged ion, and sulfur gains those electrons to become a negatively charged ion, resulting in a strong electrostatic attraction between the two.
• In sodium iodide (NaI), sodium donates an electron to iodine, thereby forming an ionic compound.

The key features of ionic bonds include:

• Formation of crystalline structures
• Typically high melting and boiling points
• Often soluble in water
• Conduct electricity when melted or dissolved

Understanding ionic bonds is crucial, particularly in predicting the behavior of salts in various conditions.

Polar Covalent Bonds

Polar covalent bonds are a type of chemical bond where a pair of electrons is unequally shared between two atoms. This occurs when the atoms involved have different electronegativities.
Examples include:

• Sulfur dioxide (SO₂), where the difference in electronegativity between sulfur and oxygen results in a polar covalent bond. This bond has a dipole moment, meaning it has a directional characteristic towards the more electronegative atom, oxygen.
• Carbon tetrachloride (CCl₄) also demonstrates polar covalent bonding, although its symmetry makes it nonpolar overall.

Polar covalent bonds have defining traits:

• Partial positive and negative charges on the atoms
• Higher melting and boiling points compared to nonpolar covalent compounds
• Increased solubility in polar solvents

Recognizing polar covalent bonds can help in understanding the solubility and reactivity of molecules in different environments.

Nonpolar Covalent Bonds

Nonpolar covalent bonds occur when two atoms share electrons equally due to similar electronegativities. This results in the absence of any distinct charge on the molecule.
A good example is:

• Hydrogen (H₂), where both hydrogen atoms have the same electronegativity, leading to an equal sharing of electrons.

Characteristics of nonpolar covalent bonds include:

• No partial charges
• Usually lower melting and boiling points compared to polar covalent and ionic compounds
• Generally insoluble in water, but soluble in nonpolar solvents like oils and fats

Understanding nonpolar covalent bonds helps predict how molecules will interact with other substances and their role in biological processes.