Three novel ether-functionalized ionic liquids (ILs) 1-ethyl-3-(2-methoxyethyl)-imidazolium acetate, [C(2)2O1IM][OAc], 1-ethyl-3-(2-methoxyethyl)-imidazolium thiocyanate, [C(2)2O1IM][SCN], 1-ethyl-3-(2-methoxyethyl)- imidazolium trifluoromethanesulfonate, [C(2)2O1IM][TfO], and two ILs 1-ethyl-3-(2-meth oxyethyl)-imidazolium dicyanamide, [C(2)2O1IM][DCA], 1-ethyl-3-(2-methoxyethyl)-imidazolium bis(tri fluoromethylsulfonyl) imide, [C(2)2O1IM][NTF2] were prepared and characterized. Their density and surface tension were measured at T = (298.15-338.15) K. As a new theoretical model, the ionic molar surface Gibbs free energy, g(i), was put forward. The ionic molar surface Gibbs free energy, g(-), for [BF4](-), which was as reference ion, was obtained in terms of the extrathermodynamic assumptions so that the ionic molar surface Gibbs free energy, g(+), of the corresponding cations, [C(n)mim](+) (n = 2-6), were determined. In terms of the g(+) values of [C(n)mim](+) (n = 2-6), the g(-) values of 12 kinds of anions were determined and then the average g(+) value of [C(2)2O1IM](+) (9.52 +/- 0.21 kJ.mol(-1)) was gotten. By using the values of these gi, the predicted values of molar surface Gibbs free energy, g(est), and surface tension, gamma(est), for [C(2)2O1IM][X] (X = OAC, SCN, DCA, TfO, NTF2) and other 45 ionic liquids were estimated. In comparison, the predicted values correlated quite well with their matching experimental values. (C) 2017 Published by Elsevier Ltd.