The radius of the H− anion also does not fit the trend of increasing size going down the halogens: indeed, H− is very diffuse because its single proton cannot easily control both electrons.
ðə ɹˈeɪdɪəs ʌvðɪ ˈeɪtʃ mˈaɪnəs ˈænaɪən ˈɔːlsoʊ dʌznˌɑːt fˈɪt ðə tɹˈɛnd ʌv ɪŋkɹˈiːsɪŋ sˈaɪz ɡˌoʊɪŋ dˌaʊn ðə hˈælədʒənz: ˌɪndˈiːd, ˈeɪtʃ mˈaɪnəs ɪz vˈɛɹi dᵻfjˈuːz bɪkˈʌz ɪts sˈɪŋɡəl pɹˈoʊtɑːn kænˈɑːt ˈiːzili kəntɹˈoʊl bˈoʊθ ᵻlˈɛktɹɑːnz.