Problem 57 - Chemistry The Science in Context

Question

Which of the following bonds are polar: \(\mathrm{C}-\mathrm{Se}, \mathrm{C}-\mathrm{O}\) \(\mathrm{Cl}-\mathrm{Cl}, \mathrm{O}=\mathrm{O}, \mathrm{N}-\mathrm{H}, \mathrm{C}-\mathrm{H} ?\) In the bond or bonds that you selected, which atom has the greater electronegativity?

Step-by-Step Solution

Answer

Answer: The polar bonds are C-O, N-H, and C-H (weakly polar). In these bonds, the atoms with greater electronegativity are O, N, and C, respectively.

Step 1: Write down the electronegativity values for each atom involved in the bonds

We can find the electronegativity values for the atoms from a periodic table or from reference materials: C: 2.55 Se: 2.55 O: 3.44 Cl: 3.16 N: 3.04 H: 2.20

Step 2: Calculate the electronegativity differences for each bond

Subtract the smaller electronegativity value from the larger one for each bond: C-Se: |2.55 - 2.55| = 0.0 C-O: |2.55 - 3.44| = 0.89 Cl-Cl: |3.16 - 3.16| = 0.0 O=O: |3.44 - 3.44| = 0.0 N-H: |3.04 - 2.20| = 0.84 C-H: |2.55 - 2.20| = 0.35

Step 3: Identify the polar bonds

A bond is considered polar if the electronegativity difference is significant (typically greater than 0.4). Based on this criterion, we have the following polar bonds: C-O (0.89) N-H (0.84) C-H (0.35) (This bond is considered weakly polar) We can see that the nonpolar bonds are C-Se, Cl-Cl, and O=O.

Step 4: Identify the atoms with greater electronegativity in the polar bonds

For the three polar bonds identified, we can now determine which atom has greater electronegativity: C-O: O has a greater electronegativity (3.44) than C (2.55) N-H: N has a greater electronegativity (3.04) than H (2.20) C-H: C has a greater electronegativity (2.55) than H (2.20) So, in conclusion, the polar bonds are C-O, N-H, and C-H (weakly polar). The atoms with greater electronegativity in these bonds are O, N, and C, respectively.

Key Concepts

Understanding Polar Bonds

Polar bonds occur when two atoms have a significant difference in electronegativity—a measure of an atom's tendency to attract electrons in a bond. This difference causes electrons to be drawn more towards one atom, creating a dipole moment, where one end of the bond is slightly negative, and the other is slightly positive.

For instance:

• In a C-O bond, oxygen is more electronegative than carbon, attracting more electrons and creating a polar bond.
• In an N-H bond, nitrogen, being more electronegative than hydrogen, causes the bond to be polar.
• The C-H bond is weakly polar as carbon's electronegativity is slightly higher than hydrogen's.

Polar bonds are contrasted with nonpolar bonds, where the electrons are shared more equally due to similar electronegativity. Examples include Cl-Cl and O=O, where atoms share electrons evenly due to identical electronegativities.

Introduction to Chemical Bonding

Chemical bonding is the process where atoms combine by sharing or transferring electrons to achieve stability. Atoms bond to achieve a full outer electron shell, leading to lower energy and greater stability. There are two primary types of chemical bonds:

• **Ionic Bonds:** Formed when one atom donates an electron to another, creating ions. These bonds usually occur between metals and nonmetals.
• **Covalent Bonds:** Occur when atoms share electrons. If the sharing is unequal due to differing electronegativities, the bond becomes polar.

Covalent bonds can further be classified based on polarity:

• **Polar Covalent Bonds:** Unequal sharing of electrons due to differences in electronegativity, like the C-O bond.
• **Nonpolar Covalent Bonds:** Equal sharing of electrons, found in bonds like Cl-Cl.

Understanding these basic principles helps explain why certain molecules have specific properties such as solubility, reactivity, and electrical conductivity.

How the Periodic Table Guides Electronegativity

The periodic table is a valuable tool for predicting and understanding chemical bonding and electronegativity. Elements are arranged in a way that demonstrates recurring trends in properties, including:

• **Electronegativity Trends:** As you move from left to right across a period, electronegativity increases. This happens because atoms attract electrons more strongly as their nuclear charge increases.
• **Group Trends:** Moving down a group, electronegativity decreases. Added electron shells increase distance from the nucleus, weakening attraction to electrons.

A practical example is comparing the electronegativity of elements involved in polar bonds, such as oxygen and nitrogen, which are located to the right of the periodic table and exhibit higher electronegativity than elements like carbon or hydrogen.
By consulting the periodic table, one can predict the behavior of different elements in chemical reactions and understand why certain bonds are more polar than others. It's a key resource for both understanding bonds and predicting molecular properties.