Using the Periodic Table to Support Our Claim

Oct 13, 2025 by wbrum.org 5 views

Which Compound Likely Has a Higher Melting Point: Aluminum Trichloride or Phosphorus Trichloride?

When it comes to determining the melting point of a compound, several factors come into play. These include the type of bonds present in the molecule, the strength of the intermolecular forces, and the molecular weight of the compound. In this article, we will explore the melting points of aluminum trichloride ( ${$ \text{AlCl}_3$} $) and phosphorus trichloride ($ { $\text{PCl}_3\$}$ ) and use the periodic table to support our claim.

Melting points are a measure of the temperature at which a solid changes state to become a liquid. This occurs when the intermolecular forces between the molecules are overcome by the thermal energy. The strength of these intermolecular forces is influenced by the type of bonds present in the molecule. In the case of aluminum trichloride and phosphorus trichloride, both compounds are ionic and molecular, respectively.

Aluminum Trichloride ( ${$ \text{AlCl}_3$}$)

Aluminum trichloride is an ionic compound composed of aluminum ions ( ${$ \text{Al}^{3+}$} $) and chloride ions ($ { $\text{Cl}^{-}\$}$ ). The ionic bonds between these ions are strong and result in a high melting point. According to the periodic table, aluminum is a metal in group 13, and chlorine is a nonmetal in group 17. The difference in electronegativity between these elements is significant, resulting in a strong ionic bond.

Phosphorus Trichloride ( ${$ \text{PCl}_3$}$)

Phosphorus trichloride is a molecular compound composed of phosphorus and chlorine atoms. The bonds between these atoms are covalent, resulting in a lower melting point compared to aluminum trichloride. According to the periodic table, phosphorus is a nonmetal in group 15, and chlorine is a nonmetal in group 17. The difference in electronegativity between these elements is less significant compared to aluminum and chlorine, resulting in a weaker covalent bond.

Using the Periodic Table to Support Our Claim

The periodic table is a powerful tool for predicting the properties of elements and compounds. By examining the position of aluminum and phosphorus in the periodic table, we can infer the strength of their bonds and, subsequently, their melting points.

Group Trends

As we move across a period in the periodic table, the electronegativity of the elements increases. This results in stronger ionic bonds between metals and nonmetals. In the case of aluminum and phosphorus, aluminum is in group 13, and phosphorus is in group 15. The difference in electronegativity between these elements is significant, resulting in a stronger ionic bond in aluminum trichloride.

Periodic Trends

As we move down a group in the periodic table, the atomic radius of the elements increases. This results in weaker intermolecular forces between molecules. In the case of phosphorus and chlorine, phosphorus is in group 15, and chlorine is in group 17. The difference in atomic radius between these elements is significant, resulting in weaker intermolecular forces in phosphorus trichloride.

Based on the analysis of the bonds present in aluminum trichloride and phosphorus trichloride, we can conclude that aluminum trichloride has a higher melting point than phosphorus trichloride. The ionic bonds between aluminum and chloride ions in aluminum trichloride result in a stronger intermolecular force, leading to a higher melting point. In contrast, the covalent bonds between phosphorus and chlorine atoms in phosphorus trichloride result in a weaker intermolecular force, leading to a lower melting point.

Melting Points of Aluminum Trichloride and Phosphorus Trichloride

Compound	Melting Point ( ${$ \text{°C}$}$)
Aluminum Trichloride ( ${$ \text{AlCl}_3$}$)	192.4
Phosphorus Trichloride ( ${$ \text{PCl}_3$}$)	-68.5

As we can see from the table above, aluminum trichloride has a melting point of 192.4 ${$ \text{°C}$}$, while phosphorus trichloride has a melting point of -68.5 ${$ \text{°C}$}$. This supports our claim that aluminum trichloride has a higher melting point than phosphorus trichloride.

CRC Handbook of Chemistry and Physics, 97th ed. (2016)
The Periodic Table of Elements, Royal Society of Chemistry (2019)
Chemistry: An Atoms First Approach, 2nd ed. by Steven S. Zumdahl (2013)

Note: The references provided are for informational purposes only and are not intended to be a comprehensive list of sources.
Q&A: Aluminum Trichloride and Phosphorus Trichloride

In our previous article, we explored the melting points of aluminum trichloride ( ${$ \text{AlCl}_3$} $) and phosphorus trichloride ($ { $\text{PCl}_3\$}$ ) and used the periodic table to support our claim. In this article, we will answer some frequently asked questions about these compounds.

Q: What is the difference between aluminum trichloride and phosphorus trichloride?

A: Aluminum trichloride is an ionic compound composed of aluminum ions ( ${$ \text{Al}^{3+}$} $) and chloride ions ($ { $\text{Cl}^{-}\$}$ ), while phosphorus trichloride is a molecular compound composed of phosphorus and chlorine atoms.

Q: Why does aluminum trichloride have a higher melting point than phosphorus trichloride?

A: Aluminum trichloride has a higher melting point than phosphorus trichloride because of the stronger ionic bonds between aluminum and chloride ions. These bonds result in a higher intermolecular force, leading to a higher melting point.

Q: What is the significance of the periodic table in determining the properties of elements and compounds?

A: The periodic table is a powerful tool for predicting the properties of elements and compounds. By examining the position of elements in the periodic table, we can infer the strength of their bonds and, subsequently, their melting points.

Q: How do the group trends and periodic trends affect the melting points of aluminum trichloride and phosphorus trichloride?

A: As we move across a period in the periodic table, the electronegativity of the elements increases, resulting in stronger ionic bonds between metals and nonmetals. In the case of aluminum and phosphorus, aluminum is in group 13, and phosphorus is in group 15. The difference in electronegativity between these elements is significant, resulting in a stronger ionic bond in aluminum trichloride. As we move down a group in the periodic table, the atomic radius of the elements increases, resulting in weaker intermolecular forces between molecules. In the case of phosphorus and chlorine, phosphorus is in group 15, and chlorine is in group 17. The difference in atomic radius between these elements is significant, resulting in weaker intermolecular forces in phosphorus trichloride.

Q: What are the melting points of aluminum trichloride and phosphorus trichloride?

A: The melting points of aluminum trichloride and phosphorus trichloride are 192.4 ${$ \text{°C}$}$ and -68.5 ${$ \text{°C}$}$, respectively.

Q: Why is it important to understand the properties of aluminum trichloride and phosphorus trichloride?

A: Understanding the properties of aluminum trichloride and phosphorus trichloride is important in various fields, including chemistry, materials science, and engineering. These compounds are used in a wide range of applications, including the production of semiconductors, catalysts, and pharmaceuticals.

Q: What are some common applications of aluminum trichloride and phosphorus trichloride?

A: Aluminum trichloride is used in the production of semiconductors, catalysts, and pharmaceuticals. Phosphorus trichloride is used in the production of pesticides, herbicides, and pharmaceuticals.

In conclusion, aluminum trichloride and phosphorus trichloride are two compounds with distinct properties. Understanding the differences between these compounds is essential in various fields, including chemistry, materials science, and engineering. By examining the periodic table and the properties of these compounds, we can gain a deeper understanding of their behavior and applications.

CRC Handbook of Chemistry and Physics, 97th ed. (2016)
The Periodic Table of Elements, Royal Society of Chemistry (2019)
Chemistry: An Atoms First Approach, 2nd ed. by Steven S. Zumdahl (2013)

Note: The references provided are for informational purposes only and are not intended to be a comprehensive list of sources.