Summarizing Comments and Rules

Despite the individual complexities of the systems surveyed here, several simple rules must have emerged in the reader s mind. Aside from the omnipresent site-blocking geometric effects, chemical or classical promotion can be understood, at least qualitatively, in terms of two simple and complementary mles, already outlined is section 2.5  

Rule 1 Electropositive adsorbates strengthen the chemisorptive bond of electron acceptor (electronegative) adsorbates and weaken the chemisorptive bond of electron donor (electropositive) adsorbates. 

These rules must be supplemented by the following two amphoteric rules already discussed in section 2.3.2.1, which supplement the definition of electron acceptor and electron donor adsorbates. 

Rule 3 In presence of a strong electron donor (electropositive) adsorbate (e.g. K, Na) a weaker electron donor (e.g. NO on Pt(lll)) behaves as an electron acceptor. 

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