Periodic Trends
As you move down Group 18, atomic radius generally ___.
Increases
At room temperature, what state are all noble gases in?
Gas
Why are noble gases generally unreactive?
They all have full outer electron shells
Which noble gas is used to fill balloons and airships?
Helium
Who discovered Argon in 1894?
Lord Rayleigh and Sir William Ramsay
What happens to the ionization energy of noble gases as you move down the group? and why?
“It decreases because the outer electrons are farther from the nucleus in larger atoms, so they are less strongly attracted and easier to remove.”
Describe the appearance and smell of noble gases.
Answer: “They are colorless, odorless, and tasteless.”
Do noble gases react with water, oxygen, or acids under normal conditions?
Answer: “No, they do not react with water, oxygen, or acids under normal conditions.”
Which noble gas is commonly used in bright, colorful signs?
Neon
Who discovered Neon, Krypton, and Xenon?
Sir William Ramsay and Morris Travers
Why do outer electrons in heavier noble gases require less energy to remove?
Answer: “Because the electrons are farther from the nucleus and are less strongly attracted.”
Which property increases slightly down the group due to larger atomic size?
Atomic radius
Which noble gases are completely unreactive?
Answer: “Helium and Neon.”
Xenon is used in flash lamps and headlights — what property makes it useful here?
It emits bright white light when excited electrically.
Who discovered Helium on the Sun before it was found on Earth?
Pierre Janssen and Norman Lockyer
Which noble gas is most likely to form compounds due to its size and lower ionization energy?
Xenon
Which noble gases can form compounds under special conditions, and why?
Answer: “Xenon and Krypton can form compounds under extreme conditions, like high pressure or with reactive elements such as fluorine, because their larger atoms have outer electrons that are slightly less tightly held.”
Which noble gas can form XeF₂, XeF₄, and XeF₆ with fluorine?
Xenon
Why is Argon used in welding and metal manufacturing?
It provides an inert environment that prevents oxidation and contamination of metals.
Which scientist received the Nobel Prize for discovering the noble gases?
Sir William Ramsay
Describe how atomic radius, ionization energy, and electronegativity together explain why noble gases are mostly unreactive, but heavier ones like Xenon can react under certain conditions.
Answer: “As atomic radius increases, the outer electrons are farther from the nucleus, reducing ionization energy. Full valence shells make noble gases generally unreactive, but in heavier gases like Xenon, the outer electrons are held less tightly, allowing them to form compounds under extreme conditions.”
Explain how the combination of being low-density gases and chemically inert affects how noble gases are used in real-life applications.
Answer: “Because noble gases are light, non-toxic, non-flammable, and chemically inert, they are safe to use in applications like filling balloons (Helium), providing an inert atmosphere in welding or light bulbs (Argon), and safely performing specialized tasks without reacting with other materials.”
Explain why heavier noble gases like Xenon and Radon can form compounds, while lighter gases like Helium and Neon cannot.
Answer: “Heavier noble gases have larger atoms, so their outer electrons are farther from the nucleus and held less tightly. This allows them to be involved in chemical bonding under extreme conditions, whereas lighter gases have tightly held electrons and remain completely inert.”
Explain why noble gases are suitable for these uses, considering their physical and chemical properties.
Answer: “Noble gases are chemically inert, non-toxic, non-flammable, and stable at high temperatures. These properties make them safe and reliable for uses in balloons (Helium), protective atmospheres (Argon), lighting and indicators (Neon, Krypton, Xenon), and medical applications (Radon).”
Why was Neil Bartlett’s 1962 discovery of xenon hexafluoroplatinate (XePtF₆) groundbreaking for chemistry?
It proved that even “inert” noble gases could form stable compounds under special conditions, changing how scientists understood chemical reactivity.