At the bottom of the periodic table, the inert-pair effect is quite strong, because of the relativistic stabilisation of the 6s orbital and the decreasing bond energy as the atoms increase in size so that the amount of energy released in forming two more bonds is not worth the high ionisation energies of the 6s electrons.
æt ðə bˈɑːɾəm ʌvðə pˌiəɹɪˈɑːdɪk tˈeɪbəl, ðɪ ɪnˈɜːtpˈɛɹ ɪfˈɛkt ɪz kwˈaɪt stɹˈɔŋ, bɪkˈʌz ʌvðə ɹˌɛləɾɪvˈɪstɪk stˌeɪbɪləzˈeɪʃən ʌvðə sˈɪks ᵻz ˈɔːɹbɪɾəl ænd ðə dˈiːkɹiːsɪŋ bˈɑːnd ˈɛnɚdʒi æz ðɪ ˈæɾəmz ˈɪŋkɹiːs ɪn sˈaɪz sˌoʊ ðætðɪ ɐmˈaʊnt ʌv ˈɛnɚdʒi ɹᵻlˈiːst ɪn fˈɔːɹmɪŋ tˈuː mˈoːɹ bˈɑːndz ɪz nˌɑːt wˈɜːθ ðə hˈaɪ ˌaɪənəzˈeɪʃən ˈɛnɚdʒiz ʌvðə sˈɪks ᵻz ᵻlˈɛktɹɑːnz.