Amphoteric oxide

...In contrast, for elements that are intermediate between the nonmetallic and metallic elements, as mentioned above, the electronegativity of the nonmetallic element is low, and as the metallicity increases, the oxide is more likely to form a macromolecule rather than a single molecule (becoming less soluble in water), and the acidity weakens (Sb ₂ O ₅ , TeO ₃ , etc.). As the electronegativity of a metallic element increases, the bond with oxygen becomes less ionic, the covalent nature increases, the basicity decreases, the element becomes less soluble in water, and the acidity increases. When this becomes extreme, for example, Al ₂ O ₃ , ZnO, PbO, SnO, etc., have intermediate properties between acid and base, that is, they act as a base against strong acids and as an acid against strong bases, so they are called amphoteric oxides. When several oxides of the same element are formed, the oxide with the higher oxidation number is more acidic, and the oxide with the lower oxidation number is more basic. ...

*Some of the terminology that mentions "amphoteric oxide" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…これらに対し上記のような非金属元素と金属元素との中間にある元素では，非金属元素でも電気陰性度が低くなり，金属性が増すと，その酸化物は単分子からなるよりも巨大分子をつくりやすくなり(水に難溶性となる)，酸性は弱まってくるし(Sb₂O₅,TeO₃など)，金属元素でも電気陰性度が増してくると酸素との結合はイオン性を減じ，共有性が増してきて塩基性が減り，水に溶けにくくなり，酸性が増す。それが極端になったとき，たとえばAl₂O₃,ZnO,PbO,SnOなどでは，酸と塩基の中間的性質，すなわち強酸に対しては塩基，強塩基に対しては酸として働くので，両性酸化物amphoteric oxideといっている。一つの元素でいくつかの酸化数の酸化物をつくるときは，高酸化数酸化物のほうが酸性が強く，低酸化数のほうが塩基性が強い。…

※「amphoteric oxide」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報