Chloroform, CHCl3, has a boiling point of 62 oC, whereas methane, CH4, has a much lower boiling point of -164 oC. Using diagrams, explain the difference between the two boiling points.
We can't draw diagrams, figures, etc on this forum. The main differences are in the higher molar mass of CHCl3 and the fact that CHCl3 has more intermolecular forces (it is polar and CH4 is not polar).
To understand the difference in boiling points between chloroform (CHCl3) and methane (CH4), we first need to grasp the concept of intermolecular forces. Intermolecular forces are attractive forces that occur between molecules and play a crucial role in determining boiling points.
Chloroform and methane both consist of carbon and hydrogen atoms, but their molecular structures are different. Chloroform has one carbon atom bonded to three hydrogen atoms and one chlorine atom (CHCl3). Methane, on the other hand, contains only carbon and hydrogen, with one carbon atom bonded to four hydrogen atoms (CH4).
Now, let's analyze the intermolecular forces in each compound using Lewis dot structures and molecular shape diagrams.
1. Chloroform (CHCl3):
In chloroform, the three hydrogen atoms and one chlorine atom are bonded to a central carbon atom. The molecule has a tetrahedral shape, with the chlorine atom occupying one of the corners of the tetrahedron.
The partial positive charge on hydrogen (δ+) attracts the partial negative charge on the chlorine (δ-) in the neighboring molecules. This attraction between the partially positive hydrogen atom and the partially negative chlorine atom is known as a dipole-dipole interaction. Chloroform molecules also experience weaker van der Waals forces due to temporary fluctuations in electron density.
The strength of these dipole-dipole interactions and van der Waals forces in chloroform contributes to a higher boiling point compared to methane.
2. Methane (CH4):
In methane, the four hydrogen atoms are symmetrically bonded to the central carbon atom, forming a tetrahedral molecular structure.
In methane, there are no highly electronegative atoms like chlorine present. Consequently, there are no significant dipole-dipole interactions between the individual molecules. Methane molecules only experience relatively weak van der Waals forces caused by slight fluctuations in electron distribution.
These weaker intermolecular forces in methane result in a significantly lower boiling point compared to chloroform.
In summary, the key difference between the boiling points of chloroform and methane lies in the type and strength of intermolecular forces. Chloroform has stronger dipole-dipole interactions and van der Waals forces due to the presence of an electronegative chlorine atom, leading to a higher boiling point. On the other hand, methane lacks such strong intermolecular attractions, resulting in a much lower boiling point.