Question

Without using Fig. 8.3, predict which bond in each of the following groups will be the most polar. a. \(\mathrm{C}-\mathrm{H}, \mathrm{Si}-\mathrm{H}, \mathrm{Sn}-\mathrm{H}\) b. \(\mathrm{Al}-\mathrm{Br}, \mathrm{Ga}-\mathrm{Br}, \mathrm{In}-\mathrm{Br}, \mathrm{Tl}-\mathrm{Br}\) c.\(\mathrm{C}-\mathrm{O}\) or \(\mathrm{Si}-\mathrm{O}\) d. \(\mathrm{O}-\mathrm{F}\) or \(\mathrm{O}-\mathrm{Cl}\)

Short answer

In summary, the most polar bonds for each group are: a. \(C-H\) b. \(Al-Br\) c. \(Si-O\) d. \(O-F\)

Step-by-step solution

List the given bonds and their electronegativity values.

First, we need to write down the list of given bonds and their electronegativity values. Electronegativity values can be looked up from the periodic table or other resources. Here are the given bonds and their electronegativity values: a. C-H: (C: 2.55, H: 2.20) Si-H: (Si: 1.90, H: 2.20) Sn-H: (Sn: 1.96, H: 2.20) b. Al-Br: (Al: 1.61, Br: 2.96) Ga-Br: (Ga: 1.81, Br: 2.96) In-Br: (In: 1.78, Br: 2.96) Tl-Br: (Tl: 1.62, Br: 2.96) c. C-O: (C: 2.55, O: 3.44) Si-O: (Si: 1.90, O: 3.44) d. O-F: (O: 3.44, F: 3.98) O-Cl: (O: 3.44, Cl: 3.16)

Calculate the electronegativity difference for each bond

Now, we need to calculate the electronegativity difference between the bonded atoms for each bond: a. C-H: |2.55 - 2.20| = 0.35 Si-H: |1.90 - 2.20| = 0.30 Sn-H: |1.96 - 2.20| = 0.24 b. Al-Br: |1.61 - 2.96| = 1.35 Ga-Br: |1.81 - 2.96| = 1.15 In-Br: |1.78 - 2.96| = 1.18 Tl-Br: |1.62 - 2.96| = 1.34 c. C-O: |2.55 - 3.44| = 0.89 Si-O: |1.90 - 3.44| = 1.54 d. O-F: |3.44 - 3.98| = 0.54 O-Cl: |3.44 - 3.16| = 0.28

Determine the most polar bonds in each group

Now we can compare the electronegativity differences within each group to identify the most polar bond: a. C-H is the most polar bond, as it has the highest electronegativity difference (0.35). b. Al-Br is the most polar bond, as it has the highest electronegativity difference (1.35). c. Si-O is the most polar bond, as it has the highest electronegativity difference (1.54). d. O-F is the most polar bond, as it has the highest electronegativity difference (0.54). Thus, the most polar bonds for each group are: a. C-H b. Al-Br c. Si-O d. O-F

Key concepts

Polar Bonds

A polar bond is a type of covalent bond where the electrons shared between the atoms are unequally distributed. This occurs because the atoms involved have different electronegativities, with one atom attracting the shared electrons more strongly. As a result, the bond has a slight charge difference across its ends, creating a dipole moment. This dipole moment leads to one end being slightly positive and the other slightly negative.

Polar bonds are important because they can influence properties like solubility, reactivity, and boiling point of the compounds. Understanding polar bonds is key when predicting how molecules will interact with each other and with different solvents. If a bond is polar, it might contribute to the molecule being overall polar, depending on the molecule's geometry.

When you compare bonds within the same group, the bond with the highest electronegativity difference will usually be the most polar, as seen in the exercise.

Electronegativity Difference

Electronegativity difference is the key factor in determining the polarity of a bond. Electronegativity itself is a measure of an atom's ability to attract and hold onto electrons. The greater the difference in electronegativity between two bonded atoms, the more polar the bond will be.

For example, in the exercise provided, we calculate the electronegativity difference by taking the absolute difference \[| ext{Electronegativity of Atom A} - ext{Electronegativity of Atom B} |\] This calculation helps to determine which atom possesses a stronger pull on the shared electrons. When the difference is zero, the bond is considered nonpolar covalent. When the difference is small, the bond is often considered polar covalent. If the difference is very large, the bond might even be considered ionic.

Understanding these differences gives insight into the nature of chemical bonds and helps to predict molecular interactions and properties.

Periodic Table Trends

The periodic table is an essential tool for predicting electronegativity and understanding why atoms behave the way they do in bonds. General trends are observed when moving across periods or down groups in the table.

• As you move from left to right across a period, electronegativity tends to increase. This is because the nuclear charge increases, pulling electrons closer to the nucleus.
• Conversely, as you move down a group, electronegativity tends to decrease. This decrease happens because the atomic size increases, making it difficult for the nucleus to attract bonding electrons effectively.

These trends allow us to predict the relative electronegativities of different elements without looking up specific values. For instance, knowing that oxygen is more electronegative than silicon helps to predict that the Si-O bond is more polar than the C-O bond, as seen in the exercise.

By leveraging these periodic trends, you can effectively predict bond polarities in a variety of chemical compounds without needing to memorize extensive data.