Name: atomic mass and mole calculations
Uploaded: 2023-06-23T15:38:52.000Z
Duration: 1 min 25 s
Channel: JoVE

元素的原子量，有时称为原子质量，约等于质子数与中子数之和。原子量以原子质量单位表示，简称 amu 或道尔顿（Daltons），在元素周期表上通常标注在其化学符号附近。
但是，大多数元素都有几种同位素，它们的中子数不同，因此质量也不同。
对于这些元素，原子量是该元素所有同位素质量的平均值，根据它们在自然界中的相对丰度或每种同位素所占的百分比进行加权计算。
例如，氯有两种天然存在的同位素。氯-35 的质量为 34.97 amu，氯-37 的质量为 36.97&#160; amu。
将氯-35（75.77%）和氯-37（24.23%）的相对丰度分别乘以其质量数，再相加，即可得到最终的原子量35.45 amu。
由于氯-35在自然界中的丰度高于氯-37，因此氯的原子量接近35 amu。

原子重量

质子和中子的质量大致相同，约为1.67 × 10-24克。科学家们将这个质量定义为一个原子质量单位（amu）或一个道尔顿。电子的质量比质子小得多，重量仅为9.11 × 10-28 克，或大约原子质量单位的1/1800。因此，它们对元素的总原子质量贡献并不大。这意味着，在考虑原子质量时，通常会忽略任何电子的质量，并且仅根据质子和中子的数量来计算原子的质量。

但是，由于大多数天然存在的元素都是由同位素组成的，因此在确定此类元素的原子质量时，考虑同位素的质量和自然丰度是非常重要的。在这种情况下，原子质量的计算方法是将所有元素同位素的质量进行相加，并且将每个同位素乘以它们的自然丰度。

化学家经常使用单位“摩尔”来表示参与化学反应的化合物原子数。元素的摩尔是其原子量（以克为单位），而化合物的摩尔是其分子的原子量之和，称为相对分子质量。一个常用的例子是使用化学式C6H12O6来计算葡萄糖的摩尔数。由此可以得出碳（C）的原子量为12.011克，葡萄糖中有六个碳，总原子量为72.066克。对氢(H)和氧(O)来进行相同的计算，葡萄糖中的相对分子质量等于180.156克。

本文部分改编自 <a href="https://openstax.org/books/biology-ap-courses/pages/2-1-atoms-isotopes-ions-and-molecules-the-building-blocks?query=atomic%20mass&target=%7B%22type%22%3A%22search%22%2C%22index%22%3A0%7D#fs-idp140338797859808">Openstax, Biology for AP</a><a href="https://openstax.org/books/biology-ap-courses/pages/2-1-atoms-isotopes-ions-and-molecules-the-building-blocks?query=atomic%20mass&target=%7B%22type%22%3A%22search%22%2C%22index%22%3A0%7D#fs-idp140338797859808">® </a><a href="https://openstax.org/books/biology-ap-courses/pages/2-1-atoms-isotopes-ions-and-molecules-the-building-blocks?query=atomic%20mass&target=%7B%22type%22%3A%22search%22%2C%22index%22%3A0%7D#fs-idp140338797859808">courses. Section 2.1 Atoms, Isotopes, Ions, and Molecules: The Building Blocks</a> and <a href="https://openstax.org/books/anatomy-and-physiology-2e/pages/2-4-inorganic-compounds-essential-to-human-functioning?query=mole&target=%7B%22type%22%3A%22search%22%2C%22index%22%3A0%7D#fs-id1218107">Openstax, Anatomy and Physiology 2e, Section 2.4 Inorganic compounds Essential to Human Functioning</a>

质子和中子的质量大致相同，约为 1.67 × 10-24 克。科学家们随意将这一质量定义为一个原子质量单位……

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Atomic Weight

atomic mass and mole calculations

Atomic mass and mole calculations help explain how much matter is in atoms and compounds. Protons and neutrons have about the same mass, about 1.67 × 10 -24 grams. Scientists define that mass as one atomic mass unit, or amu, also called one Dalton.

Electrons are much lighter than protons. They weigh only 9.11 × 10 -28 grams, or about 1/1800 of an atomic mass unit. Because of that small mass, electrons do not add much to an element’s overall atomic mass. When chemists calculate atomic mass, they usually ignore electrons and use only the protons and neutrons.

Many naturally occurring elements are made of isotopes, which are atoms of the same element with different masses. For these elements, atomic mass must include each isotope’s mass and its natural fractional abundance. Chemists find this by adding the masses of all the isotopes after multiplying each one by how common it is.

Chemists also use the mole to count atoms and compounds in reactions. A mole of an element is its atomic weight in grams. A mole of a compound is the sum of the atomic weights of its parts, and that total is called the molecular weight. Glucose, C6H12O6, is a common example. Carbon has an atomic weight of 12.011 grams, and six carbons in glucose give 72.066 grams. Doing the same for hydrogen and oxygen gives glucose a molecular weight of 180.156 grams.

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Atomic Mass and Mole Calculations

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