This module explores ionic solutions, surface phenomena like tension and surfactants, detergents, and scanning probe microscopy. It covers surface thermodynamics, properties of interfaces, and molecular behaviour at interfaces, along with experimental techniques for studying these systems. Topics include molecular interactions with solid surfaces, adsorption, Langmuir isotherms, and kinetics. Statistical thermodynamics is applied to ideal gases, considering monoatomic and diatomic gases and their translational, rotational, vibrational, and electronic contributions to the partition function.