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Ch.7 - Periodic Properties of the Elements
Chapter 7, Problem 53

Consider the first ionization energy of neon and the electron affinity of fluorine. (b) These two quantities have opposite signs. Which will be positive, and which will be negative? (c) Would you expect the magnitudes of these two quantities to be equal? If not, which one would you expect to be larger?

Verified step by step guidance
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Step 1: Define the first ionization energy and electron affinity. The first ionization energy is the energy required to remove an electron from a neutral atom in the gas phase, while electron affinity is the energy change when an electron is added to a neutral atom in the gas phase.
Step 2: Discuss the sign of each quantity. The first ionization energy is always positive because energy is required to remove an electron. Electron affinity can be negative or positive, but for most nonmetals like fluorine, it is negative because energy is released when an electron is added.
Step 3: Compare the magnitudes of the first ionization energy of neon and the electron affinity of fluorine. Neon, being a noble gas, has a high ionization energy due to its stable electron configuration. Fluorine, being highly electronegative, has a significant electron affinity, but it is generally smaller in magnitude compared to the ionization energy of a noble gas.
Step 4: Explain why the magnitudes are not equal. The stability of neon's full valence shell makes its ionization energy particularly high, while the electron affinity of fluorine, though large for a halogen, is not as high as the ionization energy of a noble gas.
Step 5: Conclude which quantity is larger. The first ionization energy of neon is expected to be larger in magnitude than the electron affinity of fluorine due to the stability and full valence shell of neon.

Key Concepts

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

Ionization Energy

Ionization energy is the energy required to remove an electron from a neutral atom in its gaseous state. For noble gases like neon, this value is typically high due to their stable electron configuration. The process is endothermic, meaning it absorbs energy, resulting in a positive value for ionization energy.
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Electron Affinity

Electron affinity is the energy change that occurs when an electron is added to a neutral atom in the gaseous state. This process can be exothermic, releasing energy, which results in a negative value for electron affinity. For elements like fluorine, which readily gain electrons, the electron affinity is significantly negative, indicating a strong tendency to attract electrons.
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Comparison of Magnitudes

While both ionization energy and electron affinity relate to electron interactions, their magnitudes are not expected to be equal. Ionization energy is generally larger than electron affinity because removing an electron from a stable configuration (like neon) requires more energy than adding an electron to a less stable configuration (like fluorine). Thus, the ionization energy of neon will be greater than the electron affinity of fluorine.
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