Explain the trend in the melting temperatures of the following tetrahedral molecules: a. CF4, 90 K b. CCl4, 250 K c. CBr4, 350 K d. CI4, 440K

Explanation:

Intermolecular forces are the forces that hold the molecules together in a substance. The state in which this substance will be at normal atmospheric conditions, and other physical properties such as boiling and melting points, are a consequence of the intermolecular forces.

The type of intermolecular force that happens in nonpolar compounds is dispersion forces. The atom or nonpolar molecule will be disturbed by the proximity of an ion or a polar molecule, thus shifting its electron cloud. The atom or nonpolar molecule will be an induced dipole.

In these tetrahedral molecules, which are not polar, the attractive forces will be London forces, which arise as a consequence of temporary induced dipoles.

Since these forces depend on proximity (the closer the proximity the larger the attraction) those molecules with a higher molar mass will have a larger electron cloud, which will be more susceptible to the effect of an induced dipole in the surroundings (the electrons are on the outer layers will be less attracted by the nuclei).

CF₄  > CCl₄ > CBr₄ >Cl₄

> Increasing size

> Increasing melting point

The melting point increases as the molecules get bigger, that is, as the number of molecules in the molecule increases.

1. for the first question, we must find the mass of the anhydrous salt, mgso₄. the molar mass for mgso₄·7h₂o is 246.47 g/mol, while that of mgso₄ is 120.37 g/mol.7.834 g mgso₄·7h₂o * 1 mol mgso₄·7h₂o/246.47 g * 1 mol mgso₄/1 mol mgso₄·7h₂o * 20.37 g mgso₄/mol = 0.647 g mgso₄

2. mass of water = mass of sample - mass of anhydrous salemass of water = 7.834 - 0.647 = 7.19 gpercent water in hydrate = 7.19/7.834 * 100 = 91.74%