[en] A radial Langmuir probe sheath model is used to make a prediction of the floating potential of a Langmuir probe immersed in an electronegative plasma. The new electronegative plasma sheath model takes into account the positive ion and the negative ion thermal energies and is valid for any ion temperature value. The values predicted can be used for diagnosing and controlling an electronegative plasma, and we compare them with measurements of the floating potential in an Argon plasma and in a Neon plasma with with two distinct electron populations at different temperatures. We have found that the agreement is very good in a wide range of plasma pressure and discharge current values, and thus the model is applicable for electronegative plasmas. Moreover, the model can be used to measure the energy with which the ions will collide with the surface of the probe. (paper)