Final answer:
CaCl₂ has the highest melting point due to ionic bonding, followed by KI with strong hydrogen bonding. NH₂OH also has hydrogen bonding but weaker than KI. PCl₃, Cl₂, and CH₄ have lower melting points due to London dispersion forces.
Step-by-step explanation:
The melting points of compounds depend on the intermolecular forces present in the substance.
In this case, we need to compare the intermolecular forces in CaCl₂, KI, NH₂OH, PCl₃, Cl₂, and CH₄.
CaCl₂ is an ionic compound, meaning it is held together by strong electrostatic interactions between the Ca²⁺ and Cl⁻ ions. This results in a high melting point.
KI and NH₂OH both have strong hydrogen bonding, which leads to higher melting points compared to substances without hydrogen bonding.
PCl₃, Cl₂, and CH₄ are molecular substances with London dispersion forces between the molecules. The larger the molecule, the stronger the London dispersion forces, resulting in higher melting points.
Therefore, arranging the compounds from highest to lowest melting point:
- CaCl₂
- KI
- NH₂OH
- PCl₃
- Cl₂
- CH₄