Chapter 19, Problem 33A

Interpretation Introduction

Interpretation: The strength of forces that holds the nucleus together and that holds the atoms together needs to be explained.

Concept introduction: Intermolecular force holds the atoms together in a molecule. Attraction of positive charge and negative charge cause atoms to stick together to form molecules. Hence intermolecular force is electrostatic in nature. Examples of intermolecular forces are,

1. Dipole-dipole forces: It is an electrostatic interactions present in molecule having permanent dipoles like hydrogen chloride.
2. London dispersion forces: This force is result of instantaneous dipole moments in mainly non-polar molecules as a result of distortion of electron charge distribution, which in turn cause the temporary induced dipole in adjacent molecules. Examples are noble gases like neon, argon and molecules like fluorine and iodine etc.

Proton present in the nucleus is positively charged. Charges of same sign repel each other and hence protons in the nucleus also repel each other. But the atom is stable because protons and the neutrons (together called nucleons) are attracted to each other by nuclear force.

Answer to Problem 33A

The nuclear force is stronger than intermolecular force.

Explanation of Solution

The nuclear force is attractive between nucleons at distances of about 1 femtometre ( $1fm={10}^{-15}m$ ), but it rapidly decreases as the distance increases. Beyond 2.5 $fm$ nuclear forces is insignificant. Whereas intermolecular force operates between atoms having more than 3 angstrom distance (1 angstrom $={10}^{-10}m$ ). The nuclear force is strongest force in nature and it is about 10 millions times stronger than the intermolecular force that holds atoms together in molecules.

Intermolecular force energy ranges in order of 5-90 kJ/mol. Nuclear force energy ranges in order ${10}^8$ - ${10}^9$ kJ/mol.

Conclusion

The nuclear force is stronger than intermolecular force.