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1.元素符号(或化学式)前面的数字,表示原子、分子或离子的个数。例如、H表示1个氢原子;2HCl表示2个氯化氢分子;3Na~+表示3个钠离子。 2.元素符号右下角的数字,表示一个分子里含有某原子的个数,或表示某离子化合物中阴、阳离子的个数比。例如,O_2中的“2”表示1个氧分子中含有2个氧原子;MgCl_2中的“1”和“2”表示Mg~(2+)与Cl~-以1:2结合成氯化镁。 3.元素符号的右上角的数字,表示一个离
1. The number in front of an element symbol (or chemical formula) indicates the number of atoms, molecules, or ions. For example, H represents one hydrogen atom; 2HCl represents two hydrogen chloride molecules; 3Na~+ represents three sodium ions. 2. The number in the lower right corner of the element symbol indicates the number of atoms in a molecule, or the ratio of the number of cations and cations in an ionic compound. For example, “2” in O 2 means that one oxygen molecule contains two oxygen atoms; “1” and “2” in MgCl 2 means that Mg 2+ and Cl~- are combined in 1 : 2 to form magnesium chloride. 3. The number in the upper right corner of the element symbol indicates a departure