This effect becomes drastically weaker for the larger sodium and potassium, allowing them to form the less stable peroxides.
ðɪs ɪfˈɛkt bɪkˌʌmz dɹˈæstɪkli wˈiːkɚ fɚðə lˈɑːɹdʒɚ sˈoʊdiəm ænd pətˈæsiəm, ɐlˈaʊɪŋ ðˌɛm tə fˈɔːɹm ðə lˈɛs stˈeɪbəl pəɹˈɑːksaɪdz.