Question

The strength Van der Waals forces increases with (1) increase in molecular size (2) increase in number of electrons in the molecule (3) increase in molecular weight (4) all are correct

Short answer

All are correct.

Step-by-step solution

Understand Van der Waals Forces

Van der Waals forces are weak attractions between molecules. These forces arise due to temporary dipoles created when electrons move around the nucleus.

Consider Molecular Size

Larger molecules have more substantial surface areas that allow more points of contact. More points of contact result in increased Van der Waals forces.

Consider the Number of Electrons

A higher number of electrons increases the probability of temporary dipoles forming within the molecule. Thus, more electrons mean stronger Van der Waals forces.

Consider Molecular Weight

An increase in molecular weight often correlates with an increase in molecular size and the number of electrons. Hence, a higher molecular weight usually signifies stronger Van der Waals forces.

Conclusion

Each factor, including molecular size, number of electrons, and molecular weight, contributes to the strength of Van der Waals forces. Therefore, all the given options are correct.

Key concepts

Molecular Size

Molecular size is crucial in determining the strength of Van der Waals forces. Larger molecules usually have bigger surface areas. This increased surface area allows more contact points between molecules.

The more contact points there are, the stronger the Van der Waals forces. Imagine trying to push together a bunch of small balloons versus a bunch of large beach balls. The larger beach balls will have more points where they touch each other.

Therefore, as the molecular size increases, the strength of Van der Waals forces also increases.

Number of Electrons

The number of electrons in a molecule also plays a significant role in the strength of Van der Waals forces. More electrons mean a higher possibility of temporary dipoles forming within the molecule.

A temporary dipole occurs when electrons move unevenly, creating a slight charge difference. This charge difference attracts other molecules briefly.

With more electrons, the chances of these temporary dipoles increase, leading to stronger Van der Waals forces.

Molecular Weight

Molecular weight is often related to both molecular size and the number of electrons. Heavier molecules generally have more substantial size and a higher number of electrons.

Thus, an increase in molecular weight usually signifies stronger Van der Waals forces. This is because more extensive and heavier molecules have more contact points and more electrons, both of which strengthen Van der Waals forces.

In summary, a higher molecular weight often results in stronger Van der Waals attractions due to these interconnected factors.