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Ch.8 - Periodic Properties of the Elements
Chapter 8, Problem 103

The lightest noble gases, such as helium and neon, are completely inert—they do not form any chemical compounds whatsoever. In contrast, the heavier noble gases do form a limited number of compounds. Explain this difference in terms of trends in fundamental periodic properties.

Verified step by step guidance
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insert step 1> The noble gases are located in Group 18 of the periodic table and are known for their lack of reactivity due to having a complete valence electron shell.
insert step 2> Helium and neon, the lightest noble gases, have very high ionization energies and small atomic radii, making it difficult for them to participate in chemical bonding.
insert step 3> As you move down the group from helium to heavier noble gases like xenon and radon, the atomic size increases, and the ionization energy decreases.
insert step 4> The decrease in ionization energy and increase in atomic size for heavier noble gases make it easier for them to form compounds, as they can more readily share or transfer electrons.
insert step 5> Additionally, the presence of d and f orbitals in heavier noble gases allows for expanded valence shells, facilitating the formation of compounds under certain conditions.

Key Concepts

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

Noble Gas Stability

Noble gases are characterized by having a complete valence shell, which makes them highly stable and unreactive. Helium and neon, being the lightest noble gases, have full outer electron shells that do not seek additional electrons, resulting in their inert nature. In contrast, heavier noble gases have larger atomic radii and can exhibit some reactivity under specific conditions, leading to the formation of compounds.
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Atomic Size and Reactivity

As you move down the periodic table, atomic size increases due to the addition of electron shells. This increase in size affects the reactivity of noble gases; heavier noble gases have more diffuse electron clouds, which can lead to interactions with other elements. The larger atomic radius can allow for some degree of polarization, enabling these gases to form weak bonds in certain compounds.
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Electronegativity and Bond Formation

Electronegativity is a measure of an atom's ability to attract and hold onto electrons. While noble gases generally have low electronegativity, heavier noble gases can exhibit slight electronegativity due to their larger size and the presence of more electrons. This allows them to engage in limited bonding with highly electronegative elements, resulting in the formation of a few stable compounds.
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Related Practice
Open Question
Consider these elements: N, Mg, O, F, Al. a. Write the electron configuration for each element. b. Arrange the elements in order of decreasing atomic radius. c. Arrange the elements in order of increasing ionization energy. d. Use the electron configurations in part a to explain the differences between your answers to parts b and c.
Open Question
Explain why atomic radius decreases as you move to the right across a period for main-group elements but not for transition elements.
Open Question
Explain why vanadium (radius = 134 pm) and copper (radius = 128 pm) have nearly identical atomic radii, even though the atomic number of copper is about 25% higher than that of vanadium. Predict the relative densities of these two metals. Look up the densities in a reference book, periodic table, or on the Internet to check if your predictions are correct.
Open Question
Why does the lightest halogen, which is also the most chemically reactive, exhibit a decrease in reactivity as you move down the column of halogens in the periodic table? Explain this trend in terms of periodic properties.
Open Question
What are the general outer electron configurations (nsx npy) for groups 6A and 7A in the periodic table? The electron affinity of each group 7A element is more negative than that of each corresponding group 6A element. Use the electron configurations to explain why this is so.
Open Question
Why is the electron affinity of each group 5A element more positive than that of each corresponding group 4A element? Use the outer electron configurations for these columns to suggest a reason for this observation.