On the basis of investigating author's opinion on citing motivations of chemistry papers aquasi-quantitative model for citing is suggested. The model selects professional and nonprofessional motivations of citing and introduces thecitation threshold concept which tries to characterize the effect of citing motivations quantitatively. Possible reasons for missing citations are also treated. Mean ages of real and of self-citations were calculated by subtracting the average of the publication years of cited papers from the publication year of the citing publication. The difference between the mean ages may characterize thesynchronity of the author's research in comparison with those working on similar topics. The paper introduces thecitation strategy indicator which relates impact factors of cited periodicals with the mean impact factor of periodicals in the corresponding research subfield.