Question

Predict which of the following bonds should be strongest: \(\mathrm{N}-\mathrm{H}, \mathrm{O}-\mathrm{H}, \mathrm{S}-\mathrm{H}\)

Short answer

The \(\mathrm{O}-\mathrm{H}\) bond is the strongest.

Step-by-step solution

Understand Bond Strength

Bond strength is determined by the bond energy required to break the bond between two atoms. A higher bond energy indicates a stronger bond.

Consider Electronegativity

Electronegativity is the tendency of an atom to attract electrons towards itself. The greater the difference in electronegativity between two bonded atoms, the stronger the bond is likely to be.

Electronegativity Values Analysis

Look up the electronegativity values: Nitrogen (3.04), Oxygen (3.44), and Sulfur (2.58). Hydrogen is the same in all bonds, so focus on the more electronegative atom in each bond.

Calculate Electronegativity Differences

Calculate the differences in electronegativity for each bond to predict bond strength: \( |3.04 - 2.20| = 0.84 \) for \( \mathrm{N}-\mathrm{H} \), \( |3.44 - 2.20| = 1.24 \) for \( \mathrm{O}-\mathrm{H} \), and \( |2.58 - 2.20| = 0.38 \) for \( \mathrm{S}-\mathrm{H} \).

Compare Electronegativity Differences

The greater the difference in electronegativity, the more polar and stronger the bond is. \( \mathrm{O}-\mathrm{H} \) has the greatest difference in electronegativity.

Determine the Strongest Bond

Since the \( \mathrm{O}-\mathrm{H} \) bond has the highest electronegativity difference, it is the strongest bond among the given options.

Key concepts

Electronegativity

Electronegativity is a key concept in chemistry that helps us understand how atoms interact with each other. It refers to the ability of an atom to attract and hold onto electrons. Think of it as the atom's pull or tug on the electrons in a bond.
Some atoms are very electronegative, which means they have a strong pull on electrons. Others are less electronegative and have a weaker pull. This property is determined by factors such as the atom's nuclear charge (how many protons are in the nucleus) and the distance of the outermost electrons from the nucleus.

• Fluorine is the most electronegative element, with a value of 3.98 on the Pauling scale.
• Electronegative atoms like oxygen and nitrogen tend to form stronger polar bonds due to their ability to attract electrons.

As you learn more about bonds, you'll see how electronegativity plays a central role in determining their characteristics and ultimately the reactivity of molecules.

Electronegativity Difference

The electronegativity difference between two atoms can tell us a lot about the type and strength of a bond they will form. This difference is simply the subtraction of the electronegativity value of one atom from that of another.
When two atoms have different electronegativities, the electrons in the bond will be more attracted to the more electronegative atom.

• If the difference is large (usually greater than 1.7), the bond is considered ionic, as electrons are more strongly attracted towards one atom, which takes on a negative charge.
• If the difference is moderate (around 0.4 to 1.7), the bond is polar covalent, meaning the electrons are shared unequally.
• A small difference (less than 0.4) indicates a nonpolar covalent bond where the electrons are shared equally.

In the context of bond strength, a higher electronegativity difference often correlates with a stronger, more polar bond.

Bond Energy

Bond energy is a measure of the strength of a chemical bond. It refers to the amount of energy required to break a bond between two atoms, resulting in separate, individual atoms.
This concept helps us understand why some molecules are more stable than others. High bond energy means the bond is strong and requires more energy to break, indicating stability.

• Strong bonds, like the \( \mathrm{O}-\mathrm{H} \) bond, have high bond energies because the atoms share electrons tightly and are held together firmly.
• Factors that affect bond energy include the size of the atoms, the number of shared electrons, and the principal energy levels involved in the bond.

Understanding bond energy gives insights into the reactivity and properties of substances and molecules.

Polar Bonds

Polar bonds are formed when two atoms share electrons unequally, resulting in a molecule with partial positive and negative charges. The atom with the higher electronegativity pulls the shared electrons closer, gaining a slight negative charge, while the other atom becomes slightly positive.
These charges create a dipole moment, which contributes to the molecule’s polarity and affects its physical properties such as solubility, boiling point, and melting point.

• Water ( H2O) is a classic example of a molecule with polar bonds due to the significant electronegativity difference between oxygen and hydrogen.
• Polar molecules tend to align themselves with electrical fields and attract other polar molecules, resulting in unique interactions such as hydrogen bonding.

These interactions are key in many biological and chemical processes, making the study of polar bonds essential for a deep understanding of chemistry.