For Pearson's qualitative HSAB theory the two properties are hardness and strength while for Drago's quantitative ECW model the two properties are electrostatic and covalent.
fɔːɹ pˈɪɹsənz kwˈɔlᵻtˌeɪɾɪv ˈeɪtʃsˈæb θˈiəɹi ðə tˈuː pɹˈɑːpɚɾiz ɑːɹ hˈɑːɹdnəs ænd stɹˈɛŋθ wˌaɪl fɔːɹ dɹˈeɪɡoʊz kwˈɔntᵻtˌeɪɾɪv ˌiːsˌiːdˈʌbəljˌuː mˈɑːdəl ðə tˈuː pɹˈɑːpɚɾiz ɑːɹ ɪlˌɛktɹoʊstˈæɾɪk ænd kˈoʊvələnt.