Problem 105 - General Chemistry: Principles and Modern Applications

Question

Which of these diatomic molecules do you think has the greater bond energy, \(\mathrm{Li}_{2}\) or \(\mathrm{C}_{2} ?\) Explain.

Step-by-Step Solution

Answer

C2 has a greater bond energy than Li2 because carbon is more electronegative and has a smaller atomic size than lithium, leading to stronger bonding.

Step 1: Understand Bond Energy

Bond energy is the amount of energy required to break one mole of a bond in a substance in gaseous state. It also represents the strength of a bond; a higher bond energy indicates a stronger bond.

Step 2: Compare Atomic Sizes and Electronegativities

Compare the atomic sizes and the electronegativities of lithium and carbon. Carbon is smaller and more electronegative than lithium. As we go across the periodic table, atomic size decreases and electronegativity increases.

Step 3: Understand the Effect on Bond Energy

A smaller atomic size and a higher electronegativity generally lead to a greater bond energy, since the bond is stronger due to the stronger pull on the shared electrons.

Step 4: deduce Bond Energy

Based on the described trends, C2 with a greater electronegativity and smaller atomic size than Li2 is likely to have a stronger bond and hence a greater bond energy.

Key Concepts

Diatomic Molecules

Diatomic molecules are simple molecules composed of two atoms. These atoms may be the same element, like hydrogen in \\( \text{H}_2 \), or different elements, like carbon monoxide in \\( \text{CO} \). These molecules are fundamental in understanding chemical bonding and interactions.

• In nature, some elements exist naturally in a diatomic state given their need to achieve stable electron configurations.
• This usually involves sharing pairs of electrons to create a covalent bond that holds the molecule together.
• The energy required to break these bonds determines the molecule's stability and reactivity.

Understanding diatomic molecules is crucial when studying bond energy because the strength and stability of these bonds directly impact chemical properties and reactions.
A strong bond in a diatomic molecule implies higher bond energy, which requires more energy to break.

Atomic Size

Atomic size refers to the distance between the center of an atom's nucleus and the outermost electrons. This concept plays a critical role in determining bond characteristics.

• A smaller atomic size generally leads to stronger bonds because electrons in smaller atoms feel a greater pull from the nucleus.
• This increased nuclear attraction can enhance bond strength within molecules such as diatomics.
• As you move across the periodic table from left to right, atomic size decreases as each successive element has more protons pulling the electrons closer.

Understanding atomic size helps predict which diatomic molecules might have higher bond energies as it influences the strength of the bond between atoms.

Electronegativity

Electronegativity is a measure of an atom's ability to attract and hold electrons within a bond. It profoundly impacts the bond energy of molecules.

• Highly electronegative atoms, such as oxygen or nitrogen, tend to form stronger bonds as they effectively attract bonding electrons.
• This results in higher bond energies, indicative of stronger bond stabilization.
• Moving across the periodic table from left to right, electronegativity generally increases.

Therefore, by understanding electronegativity, one can predict how different elements will bond with each other, both in terms of strength and energy required to break them.

Periodic Trends

Periodic trends are patterns observed in the periodic table that help predict the properties of elements. Key trends include changes in atomic size and electronegativity as one moves along periods or down groups.

• As mentioned, atomic size decreases across a period from left to right, while electronegativity increases.
• Down a group, the opposite trend is seen: atomic size increases, and electronegativity decreases.
• These trends are essential for predicting chemical reactivity, bond strengths, and properties of elements and compounds, like diatomic molecules.

By understanding periodic trends, one can better gauge the strength and stability of molecular bonds, thereby estimating bond energies in various compounds with greater accuracy.