The;linear exp-6 isotherm is presented as an approach to the thermodynamic properties of liquid alkali metals over the whole liquid range including metal-nonmetal transition. The exp-6 pair interaction potential is applied to approach the underlying interplay between the characteristics soft repulsive interaction in dense, large attractive interaction in expanded liquid alkali metal and the observed thermodynamic properties. PVT of dense liquid alkali metals obey the linear exp-6 isotherm (Z - I)V-2 = A + B rho (-7/3) exp[alpha (1 - C rho (-1/3)/r(m)) over the whole range of liquid densities, where Z is the compression factor, rho = 1/V is the density, r(m) is the position of potential minimum, alpha is a parameter, and C is a constant. The intercept A and the slope B significantly are related to attraction and repulsion, respectively, and both depend on temperature. At the level of theory presented in this study, the thermodynamic effects caused by the polarization of atoms in expanded liquid alkali metals can be accounted for by exp-6 potential function to demonstrate their thermodynamic properties as normal liquids. This includes the metal-nonmetal's transition range in which case the nature of forces is changed in such a way that the thermodynamic properties would be different from those of the high-density region. In particular, the equation of state for molten cesium is analytical over the whole range of liquid densities. The linear exp-6 isotherm is used to estimate the binding energy (0.0733 eV) and the position of potential minimum (5.336 Angstrom) of liquid cesium at freezing temperature.