Problem 7 - Chemistry: The Central Science in SI Units, Global Edition

Question

Until the early 1960 s, the group 18 elements were called the inert gases. (a) Why was the term inert gases dropped? (b) What discovery triggered this change in name? (c) What name is applied to the group now?

Step-by-Step Solution

Answer

The term "inert gases" was dropped because it was discovered that Group 18 elements can form chemical compounds under certain conditions, despite their low reactivity. This change in name was triggered by the synthesis of xenon hexafluoroplatinate (XePtF6) by Neil Bartlett in 1962, which demonstrated that these elements are not entirely inert. The current name for Group 18 elements is "noble gases," representing their low reactivity while acknowledging their ability to participate in chemical reactions.

Step 1: (a) Reason for dropping the term "inert gases"

The term "inert gases" was dropped because it was initially believed that the group 18 elements were completely unreactive due to their full valence electron shells. However, as more knowledge was gained, it was discovered that these elements can, in fact, form chemical compounds under certain conditions, albeit they have low reactivity.

Step 2: (b) Discovery that triggered the change in name

The discovery that led to the change in the name of Group 18 elements was the synthesis of xenon hexafluoroplatinate (XePtF6) by British chemist Neil Bartlett in 1962. This was the first compound made using a Group 18 element, which demonstrated that these elements are not entirely inert and can participate in chemical reactions under certain conditions.

Step 3: (c) Current name of Group 18 elements

The current name for the Group 18 elements in the periodic table is "noble gases." This name was given as these elements show a very low reactivity due to their full valence electron shells, making it hard to form compounds with them, thus giving them an appearance of 'nobility'. However, it also acknowledges that they can still participate in chemical reactions, unlike the previous term "inert gases" which implies they are completely unreactive.

Key Concepts

Noble Gases

Noble gases are a group of elements found in Group 18 of the periodic table. These elements include helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). They were initially called "inert gases" due to the belief that they did not react with other elements. This misconception arose because they have a full valence electron shell, making them stable and hard to react under normal conditions.

• The name "noble gases" better reflects their quality of having low reactivity, similar to the aloofness often associated with nobility.
• They are colorless, odorless, and tasteless, occupying the extreme right column of the periodic table.

Each noble gas has its own unique applications due to its specific properties, making them invaluable in industries like lighting and welding.

Chemical Reactivity

The term "inert" initially used for noble gases suggested that these elements were completely non-reactive. However, this was proven to be incorrect. The chemical reactivity of noble gases is low, but not zero. This low reactivity arises from their full valence electron shells, which makes them energetically stable and unlikely to form bonds.

• Despite this stability, under special conditions such as high pressure or the presence of powerful reactants, they can form compounds.
• Xenon and krypton are examples of noble gases that can form compounds with other reactive elements.

Understanding the conditions under which these gases can react helps chemists to force reactions that were once thought impossible, broadening the scope of chemical synthesis.

Valence Electron Shells

The term "valence electron shells" refers to the outermost shell of an electron in an atom. For noble gases, these shells are full, typically with eight electrons (except for helium, which has two). This full valence shell results in maximum stability, making these gases less inclined to react with other elements.

• A full valence shell means noble gases have little tendency to gain or lose electrons, resulting in their characteristic non-reactivity.
• The concepts of valence shells help to explain why atoms form bonds; they do so to achieve a full valence shell similar to noble gases.

The stability of a full valence shell is a fundamental principle in chemistry, guiding the predictions and explanations of chemical reactivity patterns.

Xenon Hexafluoroplatinate

Xenon hexafluoroplatinate (XePtF₆) is a chemical compound that changed the understanding of noble gases. It was the first known compound involving a noble gas, synthesized by Neil Bartlett in 1962. This discovery was a pivotal moment in chemistry.

• Xenon hexafluoroplatinate demonstrated that noble gases could form chemical compounds, challenging the belief that they were completely inert.
• This compound is created by reacting xenon with platinum hexafluoride under specific conditions.

This historic synthesis opened the door to numerous further studies, ultimately leading to the discovery of more noble gas compounds that serve essential roles in scientific research.

Neil Bartlett

Neil Bartlett was a British chemist who played a critical role in changing the perception of noble gases from inert to chemically capable. In 1962, Bartlett synthesized xenon hexafluoroplatinate, a groundbreaking discovery that challenged long-held assumptions about noble gases.

• Bartlett's work demonstrated that noble gases could indeed participate in chemical reactions, under specific conditions, thus altering the scientific view on chemical inertness.
• His discovery was based on an insightful analogy with oxygen, recognizing similar ionization energies between oxygen and xenon.

Bartlett's findings taught chemists to challenge existing notions and to explore the potential of elements previously considered non-reactive, expanding our understanding of the periodic table.