What is the difference between ionic and covalent bonding when referring to molecules?

Need in all of themmm only answer if you know pls

Work = force × a. work b. energy c. distance d. momentum

Consider an insulating crystal, made up of layers of atoms. what form would you expect the temperature dependence of the phonon heat capacity to approach at extremely low temperatures if the interlayer coupling is i)very strong (rigid coupling), and ii) very weak. explain.