The IUPAC definition of atomic mass unit (amu) sets the mass of one 12C atom equal to 12 amu. We can determine the amu experimentally to be 1.66 x 10-24 (0.00000000000000000000000166) grams. Just as Avogadro's number is very large, an amu is very small.
IUPAC(International Union of Pure and Applied Chemistry 國際理論和應用化學聯合會)定義原子質量單位(amu):一個12C(碳12)原子的質量就等於12個amu。由此,我們可以定義:amu大約等於1.66 x 10-24克。正如阿佛加德羅常熟非常大,而一個amu非常小。
Therefore, the atomic weight of a 12C atom is 12 amu. 14N atom has an atomic weight of 14 amu. You can look these values up in any chemistry textbook or on the web at WebElements.
因此,一個12C(碳12)原子的原子重量是12 amu。一個14N(氮14)就是14個amu的原子重量。在任何化學課本或網路的元素周期表中,你就可以評估一個原子的數值了。
The formula weight of a substance is the sum of the atomic weights of each atom in the chemical formula. Therefore, the formula weight of benzene (C6H6) is equal to the mass of six carbon atoms (6 * 12 amu = 72 amu) plus the mass of six hydrogen atoms (6 * 1 amu = 6 amu) = 78 amu. Formula weight is commonly abbreviated FW
一種物質的化學式量是其化學式中每個原子的原子重量總和。因此,苯(C6H6)的分子量就是:(6 * 12 amu = 72 amu) + (6 * 1 amu = 6 amu) = 78 amu。化學式量通常縮寫為FW。
When the chemical formula equals the molecular formula, then the formula weight is also called the molecular weight. Therefore, as the chemical and molecular formulas of benzene are both C6H6, the molecular weight of benzene is also 78 amu. The abbreviation commonly used for molecular weight is MW.
當化學式等於分子式時,化學式量也稱為分子量。因此,苯(C6H6)的化學式和分子式都是C6H6,苯的分子量也是78 amu。而分子量的通常縮寫是MW。
但是,在很多情況下,化學式不等於分子式。一個簡單的例子就是,一般來講離子化合物就是化學式,沒有分子式,它是由陰陽離子通過靜電作用生成的。因此,離子化合物沒有分子形式的存在。有的化合物由幾個分子組成,或者含有一定數量的水分子,形成結晶水化合物(或水合物),比如CuSO4·5H2O(這是化學式)。這時的化學式要比分子式(CuSO4)多5個分子的水。水合物中的水有兩種不同的結合方式:一種是作為配體,配位在金屬離子上,稱為配位結晶水;另一種則結合在陰離子上,稱為陰離子結晶水。
The molar mass is the mass in grams of 1 mole of the substance. Molar masses (in grams) are therefore numerically equal to formula weights (in amu). In the example we've been using, this tells us that because the FW of benzene is 78 amu, then one mole of benzene must weigh 78 grams. Likewise, one mole of water (FW = 18 amu) has a molar mass of 18 grams.
摩爾質量,是1摩爾物質的克數。因此,摩爾質量的克數,從數字上是等於化學式量(amu)的。看看前面的例子,因為苯的FW是78 amu,因此,一分子的苯就是重78克。同樣地,一分子水(FW=18 amu)就有18克的摩爾質量。
(編譯)