8.8
稀有气体
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Q1: Why do noble gases have such high first ionization energies?
Noble gases possess complete valence shells with stable electron configurations, making electron removal extremely unfavorable. Their filled s and p orbitals create exceptional stability. Removing an electron requires breaking this complete octet, necessitating a large energy input. This is why noble gases exhibit the highest ionization energies periodic variation and exceptions across the periodic table.
Q2: How do noble gas properties change moving down group 18?
Descending group 18, atomic radii increase while first ionization energies decrease. Boiling points and densities also increase due to stronger London dispersion forces between larger atoms. Despite these changes, all noble gases maintain high ionization energies compared to other elements, reflecting their stable electron configurations and chemical inertness.
Q3: What does the positive electron affinity of noble gases indicate?
Positive electron affinity values mean noble gases resist gaining electrons. Their complete valence shells make adding electrons unfavorable, as incoming electrons must enter higher principal quantum shells. This resistance to electron addition, combined with high ionization energies, demonstrates why noble gases are chemically inert and rarely form compounds under normal conditions.
Q4: Why was xenon able to form compounds when other noble gases could not?
Xenon has the lowest ionization energy among noble gases, making electron removal slightly less difficult. When reacted with fluorine, the most electronegative element, xenon can form stable compounds like xenon difluoride. Neil Bartlett's 1962 discovery proved noble gases were not entirely unreactive, challenging the assumption of complete chemical inertness.
Q5: What are the main industrial applications of argon and helium?
Argon prevents tungsten filament oxidation in electric light bulbs, prolonging bulb life. It also fills fluorescent tubes mixed with mercury vapor. Helium creates inert atmospheres during welding of easily oxidizable metals and serves as a cryogenic coolant for superconducting materials. Both gases exploit noble gas chemical inertness for practical purposes.
Q6: How are xenon fluoride compounds converted to xenon oxide compounds?
Xenon oxide compounds form by replacing fluorine atoms in xenon fluorides with oxygen. For example, xenon hexafluoride reacts with water to produce xenon trioxide solution, with xenon remaining in the +6 oxidation state. Dry xenon trioxide is extremely explosive and spontaneously detonates, making these compounds highly unstable.
Q7: Why do noble gases have extremely low boiling and melting points?
Noble gases experience only weak London dispersion forces between atoms since they are monatomic and have no polar bonds. These weak intermolecular forces can hold atoms together only at very low temperatures when molecular motion is minimal. This explains why noble gases remain gaseous at room temperature despite their relatively high atomic masses.