In this thesis low temperature hydrogen radio frequency (rf) plasmas discharges are modelled numerically by using both a global model and a Particle- In-Cell (PIC) simulation. Such plasmas are of interest because of their industrial applications and for the development of negative ion sources for fusion plasmas. The global model technique was adapted and then implemented to model rf inductively coupled hydrogen plasma discharges created in the DENISE experiment, with particular attention to the negative ion chemistry. For negative ions, assumed to be mainly produced by dissociative attachment, the densities obtained are always far less than 0.1 of the electron density even under the most favourable assumptions. A new numerical scheme coupling the PIC and the global model methods was devised and implemented to model rf capacitively coupled hydrogen plasma discharges, including the effects of the chemistry in the discharge. In the scheme a PIC code and a suitably modified version of the global model code are made interact by exchanging information. The global model adds the ability to handle the neutral species kinetics to the self-consistent simulation of the charged species particles of the PIC model. The scheme was used to calculate the energy cost per electron-ion pair created in plasmas with non-Maxwellian electron energy distributions. The energy losses obtained are much less than the values calculated by assuming a Maxwellian distribution with the same electron average thermal energy. The scheme was also used to obtain the energy distribution function of positive ions arriving at the electrodes. Some distributions are compared with the energy distributions measured in the CIRIS experiment, giving a reasonable agreement. Finally, negative ions were included in the simulation of rf capacitively coupled H2 plasma discharges and the numerical scheme was used to model self-consistently their production by dissociative attachment of H2(0 < v < 9).