Answer to Question #117339 in General Chemistry for Ayda Ghodrati

Question

Are London forces, intermolecular or intramolecular forces? What is the difference between the two types of forces?
What should happen to the melting and boiling point of atoms held together by London forces when the atomic number of the atoms increases? Explain why.

Answer 1

London forces are intermolecular forces. Intramolecular forces act within molecules while intermolecular forces act between molecules. Thus, intramolecular forces are stronger than intermolecular forces. When the atomic number of an atom increases, the atom become heavier and larger, thus exhibiting stronger forces. The valence electrons are farther from the nuclei and are less tightly held thus they can easily form temporary dipoles. The melting and boiling points of atoms held together by London forces increases as the atomic number increases. This is because generally, the bigger the atom, the stronger the intermolecular forces, hence the higher melting and boiling points. Stronger intermolecular bonds require more energy to break and the energy is supplied inform of heat when boiling.