In this work, we develop a model to understand why chemisorption energies of O* and C* do not follow a linear scaling relation. Following the d-band model of chemisorption, our model combines a modified version of the Newns-Anderson hybridisation energy with effective terms for the orthogonalisation repulsion. We show that lack of linear scaling along a row of the periodic table is a consequence of the saturation of the hybridisation energy of O* for metals with lower lying d-band centres, while the hybridisation energy for C* shows little to no saturation at relevant ranges of ϵ d . We suggest a measure, ϵ s , for the highest ϵ d value at which saturation is expected. We quantify the row-dependence of scaling by determining the variation of the orthogonalisation energy with the d-band centre and show that adsorbates with similar ϵ a are likely across rows. Finally, we show that linear scaling relations can be recovered in the case of C* and O* by considering metals of the same row of the transition metal series, bar noble metals.