Question

Why do noble gases have positive electron gain enthalpy? (a) It is difficult to add an electron due to small size. (b) It is difficult to add an electron due to high electronegativity. (c) It is difficult to add an electron due to stable configuration. (d) It is difficult to add an electron due to high electron affinity.

Short answer

Noble gases have positive electron gain enthalpy due to their stable electronic configuration (ns2 np6), which makes it energetically unfavorable to add an additional electron.

Step-by-step solution

Understanding Electron Gain Enthalpy

Electron gain enthalpy (often referred to as electron affinity) is the energy change that occurs when an electron is added to a neutral atom in the gaseous state to convert it into a negative ion. For noble gases, a crucial aspect to consider is their electronic configuration.

Analyzing Noble Gases' Electronic Configuration

Noble gases have a complete octave in their outermost shell, meaning they have a stable electronic configuration. Their electronic configuration is symbolized as ns2 np6, which fills their outermost shell making it complete and stable.

Considering the Stability of Noble Gases

Due to their stable electronic configuration, noble gases are already in a low energy state. Adding an additional electron would lead to a less stable state, requiring energy input. This is why noble gases generally have a positive electron gain enthalpy, implying an energy intake is necessary for an electron to be added.

Identifying the Correct Reason for Positive Electron Gain Enthalpy

Among the listed options, the correct reason for the positive electron gain enthalpy of noble gases is their stable electronic configuration. This stability is what makes it energetically unfavorable to add an electron, thus resulting in a positive value for the electron gain enthalpy.

Key concepts

Noble Gases

Noble gases are a group of elements known for their lack of chemical reactivity. Found in the last group of the periodic table, they include helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). What makes these gases 'noble' is essentially their electronic structure; they have full outer electron shells, which means their energy levels are complete making them rather inert.

This stable configuration gives them a unique position in the table as they rarely participate in chemical reactions. Think of it as them being content with their electron setup — they simply have no need to lose or gain electrons in most circumstances, which directly influences their properties and the way they interact with other elements.

Stable Electronic Configuration

The notion of a stable electronic configuration is a critical one to grasp in the realm of chemistry. For an atom, achieving stability often means having a full set of electrons in its outermost shell, something which chemists refer to as an 'octet'. The arrangement generally looks like this: an 's' orbital containing 2 electrons and 'p' orbitals containing 6 electrons, symbolically written as ns²np⁶.

When an atom reaches this state, it's akin to finding a comfortable spot after a long day; it doesn't want to move or change. This comfort, for noble gases, comes naturally, making them very stable. Other elements, however, will often gain, lose, or share electrons to replicate this harmonic setup.

Energy Change in Atoms

Talking about energy change in atoms, particularly electron gain enthalpy, we are discussing the energy required to add an electron to an atom. It's a bit like trying to put a magnet's same poles together — they resist because they are already in a low energy, stable state.

For atoms, the measure of this resistance is given in terms of energy. If the energy is released when gaining an electron, we have what's called a negative electron gain enthalpy, which is common in many nonmetals that are eager to fill their valence shells. On the flip side, atoms like noble gases demand energy to add an electron, hence they have a positive electron gain enthalpy. This process doesn't just apply to noble gases; it serves as a guide for understanding the reactivity and chemical behavior of all elements.

Chemical Properties of Noble Gases

Despite their standoffish nature, noble gases do have some fascinating chemical properties. Their reluctance to participate in reactions stems from the stability of their electronic configuration which we've discussed. This near-perfect non-reactivity has its exceptions though, with some of the heavier noble gases like xenon and krypton forming compounds under specific, typically extreme, conditions.

Now, the term 'chemical properties' can encompass various characteristics including reactivity, potential to form compounds, and behavior under different physical conditions. Noble gases are mostly colorless, odorless, and tasteless. They are also nonflammable, which is why they're often used in lighting or as inert environments for chemical reactions where other gases might react violently. The unique properties of noble gases make them a staple in both scientific studies and various industrial applications.