Linear or piece-wise linear scaling relationships are observed when two adsorbates bind to the metal through the same atom such as C * , CH * , CH * 2 and CH * 3 , where * denotes the surface. However, it is not always observed when the binding atom is different, such as in the case of C * and O * . There is currently no a priori measure to suggest if the chemisorption energies of two arbitrary adsorbates scale with one another.