Problem 3 - Campbell Biology

Question

The reactivity of an atom arises from (A) the average distance of the outermost electron shell from the nucleus. (B) the existence of unpaired electrons in the valence shell. (C) the sum of the potential energies of all the electron shells. (D) the potential energy of the valence shell.

Step-by-Step Solution

Answer

(B) the existence of unpaired electrons in the valence shell.

Step 1: Identify core concept

Atoms interact to achieve a stable electron configuration, usually a full valence shell.

Step 2: Analyze each option

Assess each choice to determine how it relates to valence electrons and reactivity.

Step 3: Option (A) Analysis

The average distance of the outermost electron shell from the nucleus does not directly determine reactivity.

Step 4: Option (B) Analysis

The existence of unpaired electrons in the valence shell indicates potential reactivity as atoms seek to pair or fill these electrons.

Step 5: Option (C) Analysis

The sum of the potential energies of all the electron shells does not directly determine atom's reactivity.

Step 6: Option (D) Analysis

The potential energy of the valence shell relates to stability but does not directly specify reactivity sources like unpaired electrons.

Step 7: Conclusion

Based on the analysis, the correct answer is related directly to unpaired electrons in the valence shell.

Key Concepts

Valence Electrons

Valence electrons are the outermost electrons of an atom, located in the atom's highest energy level. These electrons are crucial in determining an atom's chemical properties and reactivity. Knowing the number of valence electrons helps in predicting how an atom will interact with other atoms. Atoms tend to react in ways that achieve a full valence shell, similar to the noble gases, which are very stable due to their complete valence shells. This process often involves the sharing, losing, or gaining of valence electrons, leading to the formation of bonds with other atoms.
Here are some key points about valence electrons:

• Determine the chemical reactivity of an atom.
• Involved in forming bonds such as ionic and covalent bonds.
• A full valence shell results in chemical stability.

When analyzing problems related to atomic reactivity, focus on the number and arrangement of the valence electrons.

Electron Configuration

Electron configuration refers to the distribution of electrons in an atom's orbitals. Understanding electron configuration helps explain the chemical behavior and properties of elements. Electrons are arranged in energy levels or shells, which are further divided into subshells (s, p, d, f). The arrangement follows the Pauli exclusion principle and Hund's rule, leading to a specific order of filling these subshells.
Key principles include:

• Aufbau Principle: Electrons fill the lowest energy orbitals first.
• Pauli Exclusion Principle: Each orbital can hold a maximum of two electrons with opposite spins.
• Hund's Rule: Electrons occupy degenerate orbitals singly before pairing up.

The electron configuration affects elements' position in the periodic table and their chemical reactivity. Atoms with incomplete outer shells are more likely to react to obtain a stable electron configuration.

Chemical Stability

Chemical stability of an atom refers to the tendency of an atom to resist changes to its electron configuration. Atoms achieve stability by having a full valence shell, similarly to noble gases. When atoms have incomplete valence shells, they tend to be more reactive as they seek to achieve stability by interacting with other atoms.
Important factors affecting chemical stability:

• Full valence shell: Atoms with complete outer electron shells are highly stable and unreactive.
• Unpaired Electrons: Atoms with one or more unpaired electrons in their valence shells are generally more reactive.
• Energy States: Lower energy states contribute to greater stability.

Chemical reactions often occur because atoms want to achieve a state of lower energy and greater stability. By understanding these concepts, you can predict and explain the reactivity of different elements.