Problem 114 - Introductory Chemistry Atoms First

Question

Which molecule has bonds that are the most polar covalent? (a) \(\mathrm{H}_{2}\) (b) \(\mathrm{CO}\) (c) \(\mathrm{H}_{2} \mathrm{~S}\) (d) \(\mathrm{H}_{2} \mathrm{O}\)

Step-by-Step Solution

Answer

The molecule with the most polar covalent bond is (d) \(\mathrm{H}_{2}\mathrm{O}\), as it has the highest electronegativity difference between its bonded atoms (1.4).

Step 1: Find the electronegativity values

To compare the bonds, we first need the electronegativity values of hydrogen, carbon, oxygen, and sulfur. These values can be found in an electronegativity chart or a periodic table with electronegativity values. Hydrogen (H): 2.1 Carbon (C): 2.5 Oxygen (O): 3.5 Sulfur (S): 2.6

Step 2: Calculate the electronegativity difference for each bond

Now that we have the electronegativity values, we can calculate the difference in electronegativity for each bond: (a) H-H bond in \(\mathrm{H}_{2}\): Difference: |2.1 - 2.1| = 0 (b) C-O bond in \(\mathrm{CO}\): Difference: |2.5 - 3.5| = 1.0 (c) H-S bond in \(\mathrm{H}_{2}\mathrm{S}\): Difference: |2.1 - 2.6| = 0.5 (d) H-O bond in \(\mathrm{H}_{2}\mathrm{O}\): Difference: |2.1 - 3.5| = 1.4

Step 3: Compare the electronegativity differences and find the most polar covalent bond

Comparing the electronegativity differences, we can see that the H-O bond in \(\mathrm{H}_{2}\mathrm{O}\) has the highest difference of 1.4. This indicates that the H-O bond in \(\mathrm{H}_{2}\mathrm{O}\) is the most polar covalent bond among the options given. The answer is (d) \(\mathrm{H}_{2}\mathrm{O}\).

Key Concepts

Electronegativity

Electronegativity is a chemical property that describes how strongly an atom can attract electrons towards itself. This property is crucial in understanding the behavior of atoms in molecules. The greater the electronegativity, the more an atom attracts shared electrons.
Electronegativity is often measured on the Pauling scale, where different elements have specific values. Knowing these values helps us predict how molecules will interact. It's especially important in determining the polarity of bonds.

• If two atoms have very different electronegativity values, the bond between them is likely polar.
• A small difference, or none at all, usually means the bond is nonpolar.

In the context of our exercise, calculating the electronegativity difference lets us see which molecule has the most polar covalent bonds. For example, the H-O bond showed the largest difference, making it the most polar.

Molecular Polarity

Molecular polarity refers to the distribution of electric charge around a molecule. Molecules can be polar or nonpolar, depending on how their bonds are arranged.
If a molecule has an uneven distribution of charge due to polar bonds, it is considered polar. This is because such a molecule has a positive end and a negative end, like a magnet.

• Polar molecules interact with other polar substances and are soluble in water.
• Nonpolar molecules usually mix with other nonpolar substances and are not soluble in water.

In the case of water ( H_{2}O ), the molecule is polar because of the significant electronegativity difference between hydrogen and oxygen. This difference creates a bent shape that results in an overall polar molecule.

Periodic Table Electronegativity Values

Electronegativity values are listed in the periodic table, giving each element a specific capability to attract electrons. These values help chemists understand how different elements will interact when forming compounds.
Generally, electronegativity increases across a period from left to right and decreases down a group. This trend is key when predicting bond polarity.

• Elements with high electronegativity are usually found on the right side of the periodic table.
• Elements with lower electronegativity values are often on the left.

With the help of the periodic table, we can easily find the electronegativity values needed to assess bond polarity. For instance, the values of hydrogen, carbon, oxygen, and sulfur, obtained directly from the table, enabled us to calculate which bonds in our example were most polar.