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Ch.9 - Periodic Properties of the Elements
Chapter 9, Problem 85c

Choose the element with the more negative (more exothermic) electron affinity from each pair. c. P or S

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Identify the elements in question: Phosphorus (P) and Sulfur (S).
Understand that electron affinity is the amount of energy released when an electron is added to a neutral atom in the gaseous state to form a negative ion.
Recall that electron affinity generally becomes more negative (more exothermic) as you move from left to right across a period in the periodic table, due to increasing nuclear charge.
Locate P and S on the periodic table. Both P and S are in the same period (Period 3), with S being to the right of P.
Conclude that Sulfur (S), being further to the right in the same period, has a more negative electron affinity than Phosphorus (P).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Electron Affinity

Electron affinity is the energy change that occurs when an electron is added to a neutral atom in the gas phase. A more negative electron affinity indicates that the process is more exothermic, meaning energy is released when the atom gains an electron. This property is crucial for understanding how easily an atom can accept an electron and form an anion.
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Periodic Trends

Periodic trends refer to the predictable patterns observed in the properties of elements as you move across or down the periodic table. For example, electron affinity generally increases (becomes more negative) across a period due to increasing nuclear charge, which attracts electrons more strongly. Understanding these trends helps in comparing elements like phosphorus (P) and sulfur (S) in terms of their electron affinities.
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Comparison of Elements

When comparing elements, it is essential to consider their atomic structure and position in the periodic table. Phosphorus and sulfur are both in Group 15 and Group 16, respectively, with sulfur being one period below phosphorus. This difference in position affects their electron affinity, as sulfur typically has a more negative electron affinity than phosphorus due to its larger atomic size and greater ability to stabilize the added electron.
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