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一、要正确理解化合价的含义 元素的化合价是不同元素的原子在相互作用形成化合物时所表现的一种性质。也就是说,只有元素以化合物形式存在时才表现出化合价。而像H_2、O_2、Cl_3等单质中的元素未跟其他元素结合,故在单质分子里,元素化合价为零。另外,化合价是针对“元素”的,不能说物质的化合价是多少。如果说“氢气(H_2)的化合价是零”,那是错误的。同理,也不能把化合物中元素的化合价说成是原子的化合价,如“在MgO中镁原子的化合价为+2”的说法也不对。
First, we must correctly understand the meaning of valence elements valence is the nature of the different elements of the atoms in the interaction of the formation of compounds. That is, valences are only exhibited when the element is present as a compound. Elements such as H_2, O_2, Cl_3 and other elements are not combined with other elements, so the elemental valence is zero in an elemental molecule. In addition, valence is for “elements,” and it cannot be said how much the material’s valence is. If we say that the hydrogen (H_2) valence is zero, it is wrong. Similarly, it cannot be said that the valence of an element in a compound is the valence of an atom. For example, “the valence of a magnesium atom in MgO is +2” is also wrong.