Many elements had fixed valences, such as Na = +1, and O = -2, and some exhibited two or three stable valences, e.g., Cu = +1 and +2, and P = -3, +3, and +5.

• 许多元素都有固定的"化合价",诸如钠是+1价,而氧是-2价,而有些元素显两种或三种稳定的"化合价",例如铜有+1和+2价,而磷有-3、+3和+5价。