Question

Predict the type of bond (ionic, covalent, or polar covalent) one would expect to form between the following pairs of elements. a. \(\mathrm{Rb}\) and \(\mathrm{Cl}\) d. \(\mathrm{Ba}\) and \(\mathrm{S}\) b. S and S e. \(\mathrm{N}\) and \(\mathrm{P}\) c. \(\mathrm{C}\) and \(\mathrm{F}\) f. \(\mathrm{B}\) and \(\mathrm{H}\)

Short answer

The predicted bond types for the given pairs of elements are as follows: a. Rb and Cl: ionic bond d. Ba and S: polar covalent bond b. S and S: nonpolar covalent bond e. N and P: polar covalent bond c. C and F: polar covalent bond f. B and H: nonpolar covalent bond

Step-by-step solution

1. Determine electronegativity values for each element

Refer to the periodic table or other sources and find the electronegativity values for each element mentioned in the exercise.

2. Calculate electronegativity differences

Subtract the electronegativity values of each element in the pair to find the difference.

3. Determine the type of bond

Compare the electronegativity differences calculated in step 2 with the threshold values mentioned in the analysis to determine the type of bond for each pair. Using steps 1 through 3, we determine the bond types as follows: a. Rb and Cl Electronegativity(Rb) = 0.82 ; Electronegativity(Cl) = 3.16 Difference = \(|3.16 - 0.82|\) = 2.34 (ionic bond) d. Ba and S Electronegativity(Ba) = 0.89 ; Electronegativity(S) = 2.58 Difference = \(|2.58 - 0.89|\) = 1.69 (polar covalent bond) b. S and S Electronegativity(S) = 2.58 ; Electronegativity(S) = 2.58 Difference = \(|2.58 - 2.58|\) = 0 (nonpolar covalent bond) e. N and P Electronegativity(N) = 3.04 ; Electronegativity(P) = 2.19 Difference = \(|3.04 - 2.19|\) = 0.85 (polar covalent bond) c. C and F Electronegativity(C) = 2.55 ; Electronegativity(F) = 3.98 Difference = \(|3.98 - 2.55|\) = 1.43 (polar covalent bond) f. B and H Electronegativity(B) = 2.04 ; Electronegativity(H) = 2.20 Difference = \(|2.20 - 2.04|\) = 0.16 (nonpolar covalent bond)

Key concepts

Electronegativity

Electronegativity is a fundamental concept in chemistry that describes the tendency of an atom to attract electrons towards itself in a chemical bond. It is a dimensionless quantity often assigned to elements, with higher values indicating a greater ability to gain electrons.

Understanding electronegativity is crucial for predicting the type of bond formed between atoms. Elements with vastly different electronegativity values, generally greater than 1.7, tend to form ionic bonds, where one atom donates an electron to another, resulting in oppositely charged ions. Conversely, atoms with similar electronegativity values will share electrons, forming covalent bonds.

When atoms engage in a tug-of-war over shared electrons, this creates a polar covalent bond if the competing electronegativity values are between 0.5 and 1.7. The difference in electronegativity determines how evenly the electrons are shared, impacting the molecule’s properties, such as solubility, melting point, and reactivity.

Ionic Bond

An ionic bond is a chemical bond formed between two atoms with a large difference in electronegativity. As observed between rubidium (Rb) and chlorine (Cl) in the example, the electronegativity difference of 2.34 suggests an ionic bond.

This type of bond typically occurs between metals, which have lower electronegativity, and nonmetals, which have higher electronegativity. Metals lose electrons to form positively charged ions, also known as cations, while nonmetals gain those electrons, forming negatively charged ions or anions.

The resulting electrostatic attraction between the oppositely charged ions is the ionic bond, a primary force that holds the ions together. Ionic compounds, such as sodium chloride (table salt), usually have high melting and boiling points and conduct electricity when molten or dissolved in water due to the movement of ions.

Covalent Bond

Covalent bonds are characterized by the sharing of electrons between atoms, as opposed to the complete transfer of electrons in ionic bonds. For instance, two sulfur (S) atoms form a covalent bond by sharing electrons equally because they have the same electronegativity. This results in a nonpolar covalent bond, which has no significant charge difference across the molecule.

Covalent bonds are common in organic compounds and essential for constructing complex molecules such as proteins and DNA. They can involve the sharing of one, two, or three pairs of electrons, leading to single, double, or triple bonds, respectively. The strength of covalent bonds has a large bearing on a compound's chemistry, influencing properties such as boiling point, melting point, and how it interacts with other substances.

Polar Covalent Bond

Polar covalent bonds occur when atoms with differing electronegativity share electrons unequally. The polar covalent bond between carbon (C) and fluorine (F) is a classic example, showing an electronegativity difference of 1.43. Here, fluorine pulls the shared electrons closer to itself, creating a partial negative charge, while carbon acquires a partial positive charge.

Such a separation of charge produces a dipole, with one end of the bond being electron-rich and the other electron-deficient. This polarity can have significant effects on the physical properties of the molecule, including its reactivity, boiling and melting points, and interactions with other polar substances. Polar covalent bonds are integral to the structure and function of many biological molecules, such as water, which have distinct positive and negative ends that allow for the formation of hydrogen bonds, vital for life's processes.