Air and water stable hydrophobic ionic liquids (ILs) were synthesized: N-propyl-3-methylpyridinium bis(trifluoromethylsulfonyl)imide [C(3)3mpy][NTf2], N-hexyl-3-methylpyridinium bis(trifluoromethylsulfonyl)imide [C(6)3mpy][NTf2], and N-hexyl-4-methylpyridinium bis(trifluoromethylsulfonyl)imide [C(6)4mpy][NTf2]. Density, dynamic viscosity, and electrical conductivity of ILs were determined at atmospheric pressure in the temperature range of (278 to 353) K. The effects of methylene and methyl groups to density, dynamic viscosity, and electrical conductivity, respectively, were discussed. The thermal expansion coefficient, molecular volume, standard molar entropy, and lattice energy of the samples were estimated in terms of empirical and semi-empirical equations based on the density values. The temperature dependence on dynamic viscosity and electrical conductivity values of the ILs were discussed by Vogel-Fulcher-Tamman (VFT) and Arrhenius equations. The molar conductivities were calculated by density and electrical conductivity values. (c) 2013 Elsevier Ltd. All rights reserved.