Problem 75 - Chemistry: The Central Science

Question

Until the early 1960 s the group 8A 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 some Group 8A elements could form compounds under certain conditions, proving they were not entirely inert. The discovery that triggered this change was the synthesis of xenon hexafluoroplatinate (XePtF6) by Neil Bartlett in 1962. The current name for Group 8A elements is "noble gases," acknowledging their general chemical unreactivity while allowing for the fact that they can form compounds under specific conditions.

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

Until the early 1960s, the elements in Group 8A of the periodic table - helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn) - were called inert gases. They were considered "inert" because they were believed to be chemically unreactive due to their filled electron shells. However, it was later discovered that some of these gases could indeed form compounds under certain conditions, which demonstrated that they were not entirely inert. As a result, the term "inert gases" was dropped to avoid confusion and inaccuracies.

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

The discovery that led to the change in the name of Group 8A elements was the synthesis of the first xenon compound, xenon hexafluoroplatinate (XePtF6), by Neil Bartlett in 1962. This discovery provided evidence that these elements could form compounds under specific conditions, contradicting their previous categorization as completely unreactive. The realization that they could form compounds meant that these elements were not as inert as previously thought, leading to a shift in terminology.

Step 3: (c) Current name for Group 8A elements

Today, the elements in Group 8A of the periodic table are collectively referred to as the noble gases. The term "noble gases" is derived from the idea that these elements, like noble metals such as gold and platinum, are relatively unreactive in comparison to other elements. This name is more appropriate, as it acknowledges their general chemical unreactivity while also allowing for the fact that they can form compounds under certain conditions. So, the current name for Group 8A is the "noble gases."

Key Concepts

Group 8A Elements

The Group 8A elements, known as the noble gases, occupy a unique place on the periodic table. These elements include helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn).

Initially dubbed 'inert gases' due to their lack of reactivity, these elements feature complete valence electron shells, which contributes to their general unwillingness to participate in chemical reactions. Their electronic configuration makes these gases highly stable and unreactive under standard conditions. As you move down the group, however, the atomic size increases, and the valence electrons are farther from the nucleus. This creates slightly more reactivity for the heavier noble gases.

Students often wonder why helium, with only two electrons, is part of this group. It's because helium's filled first energy level (1s²) achieves a stable noble gas configuration. Reflecting upon the stability and non-reactivity of the noble gases provides an excellent lesson in the importance of electron configuration in predicting chemical behavior.

Chemical Reactivity of Noble Gases

For many years, the noble gases were believed to be entirely unreactive, deserving of the name 'inert.' However, research in the 20th century overturned this assumption. In 1962, chemist Neil Bartlett made a groundbreaking discovery with xenon, providing definitive proof that noble gases could form chemical compounds.

While it's true that the noble gases are less reactive than most other elements, under certain conditions – such as high pressure, the presence of powerful oxidizing agents, or electric discharge – they can engage in chemical reactions. Their reactivity increases with heavier atoms like krypton, xenon, and radon due to their larger atomic sizes and the comparatively lower ionization energy.

It is essential to distinguish between reactivity and the ability to form compounds. The 'noble' descriptor implies that, like noble metals, these gases resist reaction under typical circumstances but are not completely immune to chemical change. This nuanced understanding is key to appreciating the potential versatility of noble gases in the field of chemistry.

Xenon Hexafluoroplatinate

Xenon hexafluoroplatinate (XePtF₆) made headlines as the first compound to include a noble gas, xenon, in its structure. Before this synthesis by Neil Bartlett in 1962, the chemistry world operated under the belief that noble gases could not form compounds due to their complete valence electron shells.

This compound is produced in a two-step process. Platinum hexafluoride (PtF₆), a strong oxidizing agent, is used to oxidize xenon gas under specific conditions, leading to the formation of XePtF₆. The formation of xenon hexafluoroplatinate broke new ground in chemistry, revealing that even the least reactive elements have potential for chemical bonding.

Since this discovery, scientists have synthesized other xenon compounds, unleashing a new realm of 'noble gas chemistry.' These advances showcase that under the right conditions, such as the presence of a potent oxidizer or elevated pressures, the chemical landscape can vastly expand beyond traditional norms.