We have examined the atomic coordination effect on the local bond strain and the 3p core-level shift of K(1 1 0) skin and nanoclusters using a combination of the bond order-length-strength correlation notion, tight-binding approach, density functional theory calculations, and photoelectron spectroscopy measurements. It turns out that: (i) the 3p core-level shifts from 15.595 +/- 0.003 eV for an isolated K atom by 2.758 eV to the bulk value of 18.353 eV; (ii) the effective atomic coordination number reduces from the bulk value of 12 to 3.93 for the first layer and to 5.81 for the second layer of K(1 1 0) skin associated with the local lattice strain of 12.76%, a binding energy density 72.67%, and atomic cohesive energy -62.46% for the skin; and (iii) K cluster size reduction lowers the effective atomic coordination number and enhances further the skin electronic attribution. Results have revealed that the 3p core-level shifts of K(1 1 0) and nanoclusters originate from perturbation of the Hamiltonian by under-coordination induced charge densification and quantum entrapment. (C) 2015 Elsevier B.V. All rights reserved.