Question

List these bonds in order of increasing ionic character: cesium to fluorine, chlorine to chlorine, bromine to chlorine, silicon to carbon.

Short answer

From least to most ionic character: Chlorine to Chlorine, Bromine to Chlorine, Silicon to Carbon, and Cesium to Fluorine.

Step-by-step solution

Identify Relative Electronegativities

For each pair of atoms in a bond, check a periodic table for the electronegativities of the two elements, and take the absolute value of the difference between these two electronegativities. The pairs are: Cesium (Cs) to Fluorine (F), Chlorine (Cl) to Chlorine (Cl), Bromine (Br) to Chlorine (Cl), and Silicon (Si) to Carbon (C). According to the periodic table, the electronegativities are: Cs (0.79), F (3.98), Cl (3.16), Br (2.96), Si (1.90), and C (2.55). Therefore, the absolute differences are: Cs to F = |3.98 - 0.79| = 3.19; Cl to Cl = |3.16 - 3.16| = 0; Br to Cl = |3.16 - 2.96| = 0.2; Si to C = |2.55 - 1.90| = 0.65.

Rank the Bonds

Now, rank the bonds in order of increasing absolute electronegativity difference: Chlorine to Chlorine (0.00), Bromine to Chlorine (0.2), Silicon to Carbon (0.65), and Cesium to Fluorine (3.19). This indicates the increasing ionic character of these bonds.

Key concepts

Bond Electronegativity Difference

Understanding the bond electronegativity difference is crucial for predicting the type of bond that will form between two atoms. Electronegativity itself is a measure of the tendency of an atom to attract a bonding pair of electrons. When atoms with differing electronegativities form a bond, the shared electrons are pulled more toward the atom with the higher electronegativity, creating a polarity in the bond.
The greater the difference in electronegativity between the bonded atoms, the more polar the bond. If the difference is large enough (typically greater than 1.7), it can lead to the formation of an ionic bond where electrons are not shared but transferred from the less electronegative atom to the more electronegative one. Lesser differences usually result in covalent bonds, where electrons are more equally shared.
In the given exercise, for example, cesium to fluorine has the largest electronegativity difference, signaling a strong ionic character, while chlorine to chlorine has zero difference, indicating a pure covalent bond. These comparisons utilize the concept of electronegativity difference to predict bond character and behavior in compounds.

Periodic Table Electronegativity

The periodic table is not only a chart of elements but a map of electronegativity values. Electronegativity is not a random property; it follows a trend across the periodic table. Generally, electronegativity increases from left to right across a period and decreases down a group. This trend is due to the increase in the number of charges on the nucleus and the distance of the valence electrons from the nucleus.
When navigating the periodic table to find the electronegativity of elements for a chemistry exercise, it's essential to understand these trends. For instance, fluorine, at the top right of the periodic table, holds the highest electronegativity value, explaining why the cesium to fluorine bond has a significant ionic character due to the large difference in their electronegativities. An understanding of these trends is key to predicting the chemical behavior and bond types formed by different elements.

Chemistry Bond Types

In chemistry, there are three primary types of bonds that hold atoms together: ionic, covalent, and metallic. Ionic bonds occur between metals and nonmetals and involve the transfer of electrons, creating oppositely charged ions that attract each other. Covalent bonds happen when two nonmetals share one or more pairs of electrons, and they can be polar or nonpolar based on the electronegativity difference. Metallic bonds are between metals and involve a 'sea of electrons' that are free to move, which explains the conductivity of metals.
The exercise solution illustrates these concepts by ranking the bonds from least to most ionic character. Covalent bonds (like chlorine to chlorine) have the least ionic character due to the low or nonexistent electronegativity difference. On the other end of the spectrum, the cesium to fluorine bond is primarily ionic. By understanding the nature and characteristics of these bond types, students can more easily grasp the connections between atomic properties and the resulting chemical bonds in different substances.