Chemical Bonding and Compound States

The physical state (solid, liquid, or gas) of a chemical compound is determined by factors like its molecular structure, the type of bonding (ionic vs. covalent), polarity, molecular mass, and the strength of intermolecular forces (like van der Waals forces or ionic bonds).

Compound Properties and Volatility

We need to evaluate each option based on these properties to predict which is most likely to exist in the gaseous state:

• 1. $WF_6$ (Tungsten Hexafluoride): This compound is molecular and covalent. It has a low boiling point of $17.1^\circ C$. Because this temperature is below standard room temperature ($ \approx 25^\circ C$), $WF_6$ exists as a gas under typical ambient conditions.
• 2. $UF_4$ (Uranium Tetrafluoride): Uranium tetrafluoride is generally considered an ionic compound or a solid with significant ionic character. Ionic compounds typically form crystal lattices with strong electrostatic forces, resulting in high melting and boiling points. Thus, $UF_4$ is expected to be a solid.
• 3. $TiCl_4$ (Titanium Tetrachloride): $TiCl_4$ is a covalent molecular compound. It is a liquid at room temperature, boiling at $136.4^\circ C$. Although it's a liquid at $25^\circ C$, this boiling point is relatively low compared to ionic compounds. The weaker van der Waals forces between $TiCl_4$ molecules allow it to vaporize easily, indicating a strong tendency to exist in the gaseous state, particularly at slightly elevated temperatures or under reduced pressure. Its volatility makes it a candidate for existing in the gaseous phase.
• 4. $ScCl_3$ (Scandium Chloride): Scandium chloride ($ScCl_3$) is primarily ionic. Similar to $UF_4$, it forms a stable solid lattice with strong inter-ionic forces, leading to a very high melting point (it sublimes above $600^\circ C$). Consequently, $ScCl_3$ exists as a solid and is not expected to be gaseous under normal conditions.

Gaseous State Expectation: TiCl4

Comparing the options:

• $WF_6$ is already a gas at room temperature.
• $UF_4$ and $ScCl_3$ are stable ionic solids with very high melting points.
• $TiCl_4$, while a liquid at room temperature, is a covalent molecule with relatively weak intermolecular forces and a moderate boiling point. This suggests it readily transitions to the gaseous state compared to the ionic solids.

Therefore, among the choices provided, $TiCl_4$ is the compound expected to exist in the gaseous state, primarily due to its covalent nature and resulting volatility compared to the ionic compounds listed.