分子式Molecular formula

实验式（最简式）给出原子数的最简整数比，乙烷为 CH₃，葡萄糖为 CH₂O。分子式是实验式的整数倍。结构简式（如 CH₃CH₂OH）、结构式和骨架式进一步表示原子的连接方式。分子式相同而结构不同的化合物互为同分异构体，如 C₂H₆O 既可以是乙醇也可以是甲醚。

The empirical formula gives the simplest whole-number ratio: CH₃ for ethane, CH₂O for glucose. The molecular formula is a whole-number multiple of it. Condensed formulas (CH₃CH₂OH), displayed formulas and skeletal formulas go further and show how atoms are connected. Compounds with the same molecular formula but different structures are isomers; C₂H₆O can be ethanol or methoxymethane.

先由元素分析的质量百分数求出实验式，再由相对分子质量（如质谱分子离子峰）求倍数。例：某化合物含 C 40.0%、H 6.7%、O 53.3%，实验式为 CH₂O（式量 30），Mr = 180，故分子式为 C₆H₁₂O₆。

Find the empirical formula from the percentage composition, then use the relative molecular mass, for example from the molecular ion in a mass spectrum, to find the multiple. A compound with 40.0% C, 6.7% H and 53.3% O has empirical formula CH₂O (formula mass 30); with Mr = 180 the molecular formula is C₆H₁₂O₆.