定义Definition
阳离子是带正电荷的离子，原子或原子团失去电子后形成，如 Na⁺、Ca²⁺、Fe³⁺、NH₄⁺、H₃O⁺。电解时阳离子移向阴极（负极），在阴极得到电子。
A cation is a positively charged ion, formed when an atom or group of atoms loses electrons, such as Na⁺, Ca²⁺, Fe³⁺, NH₄⁺ and H₃O⁺. In electrolysis cations move to the cathode (negative electrode), where they gain electrons.
形成规律Which elements form cations
金属元素电离能较低，容易失去价电子形成阳离子：第 1 族形成 +1 价离子，第 2 族形成 +2 价离子，铝形成 Al³⁺。过渡金属可形成多种价态，如 Fe²⁺ 和 Fe³⁺，形成离子时先失去 4s 电子。
Metals have low ionisation energies and lose their outer electrons readily: group 1 forms +1 ions, group 2 forms +2 ions and aluminium forms Al³⁺. Transition metals can form several, such as Fe²⁺ and Fe³⁺, losing their 4s electrons first.
极化能力Polarising power
阳离子半径越小、电荷越高，电荷密度越大，越能使阴离子的电子云变形，使键带有共价性。所以 Al³⁺、Be²⁺、Li⁺ 的化合物共价性比同族较大离子的化合物明显。
The smaller and more highly charged a cation, the higher its charge density and the more it distorts an anion's electron cloud, giving the bond covalent character. Compounds of Al³⁺, Be²⁺ and Li⁺ are therefore more covalent than those of larger ions in their groups.