The smaller alkali metals tend to polarise the larger anions (the peroxide and superoxide) due to their small size.
ðə smˈɔːlɚɹ ˈælkəlˌaɪ mˈɛɾəlz tˈɛnd tə pˈoʊlɚɹˌaɪz ðə lˈɑːɹdʒɚɹ ˈænaɪənz ðə pəɹˈɑːksaɪd ænd sˌuːpɚɹˈɑːksaɪd dˈuː tə ðɛɹ smˈɔːl sˈaɪz.