Question

Among the following bonds, which are more ionic than covalent? (a) \(\mathrm{Si}-\mathrm{O}\) (b) \(\mathrm{Ba}-\mathrm{O}\) (c) \(\mathrm{Se}-\mathrm{Cl}\) (d) \(\mathrm{K}-\mathrm{Br}\)

Short answer

The bonds (b) Ba-O and (d) K-Br are more ionic than covalent.

Step-by-step solution

Understanding Ionic and Covalent Bonds

The degree to which a bond between two atoms is ionic or covalent can be determined by the difference in their electronegativities. A larger difference indicates a more ionic character while a smaller difference points to a more covalent character. Ionic bonds typically form between metals and nonmetals, with metals losing electrons and nonmetals gaining electrons.

Determining Electronegativity Differences

Look up the electronegativities of the atoms involved in each bond. Subtract the smaller electronegativity from the larger one to determine the difference. For example, if one atom has an electronegativity of 3.0 and another has 1.0, the difference is 2.0, which is indicative of a more ionic bond.

Comparison of Bond Types

Compare the electronegativity differences for each bond to determine which are more ionic. The bonds with the larger differences in electronegativity will be more ionic in character.

Identifying the Most Ionic Bonds

By comparing the electronegativity of the atoms in the given bonds, we can conclude: (a) Si-O bond involves a metalloid and a nonmetal, (b) Ba-O bond involves an alkaline earth metal and a nonmetal and will have a high electronegativity difference, (c) Se-Cl bond involves two nonmetals and will have a smaller difference, (d) K-Br bond involves an alkali metal and a halogen and will have a high electronegativity difference. Therefore, bonds (b) Ba-O and (d) K-Br are more ionic than covalent.

Key concepts

Electronegativity Difference

Electronegativity is a measure of an atom's ability to attract and hold onto electrons when it is part of a compound. When we talk about bonding, the difference in electronegativity between the two atoms involved is a crucial factor for determining the type of bond that will form. If the difference is high usually greater than 1.7, we're looking at an ionic bond, where electrons are transferred from one atom to another. On the other hand, a smaller difference suggests a covalent bond where electrons are shared.

To grasp this concept, imagine a tug-of-war game. If both players (atoms) are of approximately equal strength (electronegativity), they'll share the tug-of-war rope evenly between them – that's a covalent bond. But if one player is significantly stronger, that player will take the rope – representing an electron – mostly to their side; this is an ionic bond. In the exercises, bonds (b) Ba-O and (d) K-Br have a larger electronegativity difference indicating a more ionic character.

Metal-Nonmetal Bonding

Metal-nonmetal bonding is typically ionic. Metals, with their tendency to lose electrons and form positive ions, and nonmetals, with their inclination to gain electrons and form negative ions, come together to balance each other out. The result is a bond based on the strong attraction between opposite charges.

In our everyday lives, table salt (sodium chloride) is a perfect example of an ionic compound. Sodium (metal) gives up an electron to chlorine (nonmetal) to form Na+ and Cl- ions that are then bonded together in a crystal lattice. In the textbook exercise, both (b) Ba-O and (d) K-Br involve a metal bonding with a nonmetal, which typically leads to the formation of an ionic bond due to this transfer of electrons.

Bond Polarity

Bond polarity is all about the distribution of electrical charge between two atoms in a bond. When atoms with different electronegativities form a bond, they don't share the electrons equally, and this creates a dipole; there's a positive end and a negative end, much like a battery. The greater the electronegativity difference, the more polar the bond is.

Visualize a bond as a shared pair of electrons; if one atom hogs the electrons (like the stronger player in the tug-of-war), it becomes slightly negative, leaving the other atom slightly positive. This is essentially what's happening in a polar covalent bond. Ionic bonds are considered the extreme of polarity, as complete transfer of electrons takes place. In our exercise examples, bonds with large electronegativity differences, particularly (b) Ba-O and (d) K-Br, have high polarity, behaving much like ionic bonds.