Problem 166 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is/are solid here? (a) \(\mathrm{XeF}_{2}\) (b) \(\mathrm{XeF}_{4}\) (c) \(\mathrm{XeF}_{6}\) (d) \(\mathrm{HF}\)

Step-by-Step Solution

Answer

\(\mathrm{XeF}_{2}\) and \(\mathrm{XeF}_{4}\) are solids under normal conditions.

Step 1: Introduction to Solids Definition

A solid is defined as a state of matter characterized by definite shape and volume with particles tightly packed in a fixed arrangement. Solids exhibit structural rigidity and resistance to changes in shape or volume.

Step 2: Understanding the Substances

Each of the given substances involves xenon (Xe) as a central atom with fluorine (F) or hydrogen (H) atoms bonded to it. We need to determine which of these substances exists in solid form under normal conditions.

Step 3: Review of Molecular Formations

(a) \(\mathrm{XeF}_{2}\): This is a linear molecule. (b) \(\mathrm{XeF}_{4}\): This is a square planar molecule.(c) \(\mathrm{XeF}_{6}\): This molecule has an octahedral shape. (d) \(\mathrm{HF}\): Hydrogen fluoride can form hydrogen bonds.

Step 4: State of Each Substance

- \(\mathrm{XeF}_{2}\) becomes a solid under normal conditions.- \(\mathrm{XeF}_{4}\) is also a solid under normal conditions due to its ability to form extended structures.- \(\mathrm{XeF}_{6}\) can exist as a solid under controlled conditions. - \(\mathrm{HF}\) usually exists as a liquid under normal conditions, although it can form solid under cryogenic conditions. However, \(\mathrm{HF}\) is more commonly in liquid form than solid under normal circumstances.

Step 5: Conclusion on Solid State

Considering the properties and common states, \(\mathrm{XeF}_{2}\) and \(\mathrm{XeF}_{4}\) are often found as solids. \(\mathrm{XeF}_{6}\) can be solid but not necessarily under normal conditions, while \(\mathrm{HF}\) is typically not solid under usual conditions.

Key Concepts

Molecular Geometry

Molecular geometry is the three-dimensional arrangement of atoms in a molecule. It's crucial because it determines the molecule's properties, like polarity, reactivity, and phase of matter. The shape of a molecule is determined by the number of bonds and lone pairs around the central atom. In the context of xenon fluoride compounds:

• In \((\mathrm{XeF}_{2})\), the geometry is linear. This means the xenon atom is in between two fluorine atoms forming a straight line.
• For \((\mathrm{XeF}_{4})\), the shape is square planar. Here, the xenon atom is at the center of a square formed by four fluorine atoms.
• In \((\mathrm{XeF}_{6})\), the geometry is octahedral. The xenon is at the center of a structure with eight faces (six corners), each inhabited by a fluorine atom.

These geometrical formations influence the physical states and reactivities of these compounds.

States of Matter

States of matter refer to the distinct forms that different phases of matter take on. The four classical states are solid, liquid, gas, and plasma. For xenon compounds, the focus is on the first three.

• Solids: These have a definite shape and volume due to fixed particle positions. Molecules like \(\mathrm{XeF}_{2}\) and \(\mathrm{XeF}_{4}\) can form solid structures at room temperature because of their molecular arrangements that allow tighter packing.
• Liquids: Liquids have a definite volume but adapt to the shape of their container. \(\mathrm{HF}\) is typically a liquid under normal conditions, despite forming solid structures when cooled.
• Gases: Gases neither have a definite shape nor volume, with particles free to move in all directions. Compounds form gases under high temperatures or low pressures, which isn't typical for xenon fluorides under normal conditions.

Xenon Compounds Chemistry

Xenon compounds are compounds formed between xenon, a noble gas, and other elements. Unlike most noble gases, xenon can form stable compounds due to its ability to form bonds under specific conditions.

• Xenon Difluoride (\(\mathrm{XeF}_{2}\)): This is a valuable chemical reagent used in the synthesis of other organic and inorganic fluorides. It is a dense white solid at room temperature.
• Xenon Tetrafluoride (\(\mathrm{XeF}_{4}\)): Characterized by its square planar geometry, it is also a white solid at room temperature, used primarily for academic purposes as a source of fluorine.
• Xenon Hexafluoride (\(\mathrm{XeF}_{6}\)): This is more reactive and can exist in solid form under specific conditions, though it is less stable as a solid compared to \(\mathrm{XeF}_{2}\) and \(\mathrm{XeF}_{4}\).

Understanding xenon compounds involves recognizing the unusual capacity of a noble gas to engage in molecular bonding, making them a fascinating topic in solid-state chemistry.