Problem 29 - Chemistry: The Central Science in SI Units, Global Edition

Question

Why does xenon form stable compounds with fluorine, whereas argon does not?

Step-by-Step Solution

Answer

Xenon forms stable compounds with fluorine due to its larger atomic size, weaker hold on its outermost electrons, and the high electronegativity of fluorine, which facilitates the formation of strong Xe-F covalent bonds. In contrast, argon does not form stable compounds with fluorine because its outer electrons are more tightly held by its nucleus, making it chemically inert and less prone to form bonds with other elements.

Step 1: Compare the Electronic Configurations of Xenon and Argon

Xenon (Xe) and argon (Ar) are both noble gases in the same group of the periodic table. Their electronic configurations are such that they have a filled outer electron shell, which makes them chemically inert and stable. However, due to the difference in their atomic size and the number of electron shells, they may exhibit different chemical reactivities. Xenon has an atomic number of 54 and its electronic configuration is \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2 4d^{10} 5p^6\). Meanwhile, argon has an atomic number of 18 and its electronic configuration is \(1s^2 2s^2 2p^6 3s^2 3p^6\). Since xenon has more electron shells, its outermost electrons are further away from the nucleus, making them less tightly held and more prone to get involved in chemical reactions.

Step 2: Investigate the Properties of Fluorine

Fluorine (F), with an atomic number of 9, is a highly electronegative element and has a strong tendency to attract electrons. Its electronic configuration is \(1s^2 2s^2 2p^5\), which means it is one electron short of achieving the stable noble gas configuration. Therefore, fluorine is very reactive and forms strong bonds with other elements, including noble gases such as xenon.

Step 3: Explain the Stability of Xenon-Fluorine Compounds

The stability of xenon-fluorine compounds can be explained by the relatively weaker hold of xenon's outermost electrons by its nucleus. As a result, xenon has the ability to donate electrons to the highly electronegative fluorine atoms. This leads to the formation of stable compounds, such as xenon hexafluoride (XeF6) and xenon tetrafluoride (XeF4). These compounds are held together by strong Xe-F covalent bonds, making them chemically stable.

Step 4: Discuss the Potential Argon-Fluorine Compounds

On the other hand, argon's outer electrons are more tightly held by its nucleus due to its smaller atomic size and fewer electron shells. As a result, the energy required to form a bond between argon and fluorine would be too high and therefore not energetically favorable. In fact, there are no known stable argon-fluorine compounds under normal conditions, as argon is much less reactive than xenon. In conclusion, xenon can form stable compounds with fluorine due to the weaker hold on its outermost electrons and the high electronegativity of fluorine. However, argon does not form stable compounds with fluorine because its outer electrons are held more tightly by its nucleus, making it chemically inert and less prone to form bonds with other elements.

Key Concepts

Electronic Configuration

Electronic configuration refers to the arrangement of electrons in an atom's electron shells. Each noble gas has a unique configuration that results in a complete outer shell of electrons, making them chemically inert. This configuration is crucial in understanding why some noble gases react under certain conditions while others do not.

• Xenon: With an atomic number of 54, xenon's electronic configuration is complex, represented as \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2 4d^{10} 5p^6\). Its electrons in the outer shell are less strongly bound due to the larger atomic size and increased distance from the nucleus.
• Argon: In contrast, argon has a simpler configuration, \(1s^2 2s^2 2p^6 3s^2 3p^6\), with a tightly held outer shell due to its smaller size.

These configurations mean that xenon's outer electrons can participate in chemical reactions more readily than argon's.

Chemical Bonding

Chemical bonding involves the interaction of atoms to form compounds, and it occurs in several forms. Covalent bonding, where atoms share electrons, is essential in explaining reactions involving noble gases like xenon.

Fluorine, a highly reactive element, seeks electrons to achieve the stable noble gas configuration. When it interacts with xenon, the weaker hold that xenon has on its outer electrons allows it to form strong covalent bonds with fluorine. These bonds stabilize the newly formed xenon-fluorine compounds, such as xenon hexafluoride (XeF₆) and xenon tetrafluoride (XeF₄).

Argon, however, does not form such bonds due to the higher energy required to overcome the tightly bound outer electrons, maintaining its status as a non-reactive noble gas under standard conditions.

Noble Gas Compounds

Noble gas compounds are rare and intriguing because noble gases are generally known for their lack of reactivity. However, under certain conditions, some noble gases like xenon can form stable compounds.

• Xenon Compounds: The ability of xenon to form compounds, such as XeF₄ and XeF₆, is linked to its larger atomic size and weaker electron-nucleus attraction. These compounds illustrate xenon's capacity to participate in chemical reactions when combined with highly electronegative elements like fluorine.
• Argon Compounds: Despite numerous efforts, stable compounds of argon remain undiscovered under normal conditions. Its tightly held electrons and smaller atomic size preserve its chemical inertness, demonstrating why it doesn't form stable compounds.

Understanding noble gas compounds helps highlight the diverse chemical behavior of elements within the periodic table, emphasizing conditions under which rare reactions occur.