We measure atomic mass in atomic mass units.

我们以原子质量单位测量原子质量。

For instance, the mass of a neutral helium atom is 4.002603 unified atomic mass units.

一个稳定的氦原子核的质量是4。002603u。

The same goes for atomic mass. We measure atomic mass in atomic mass units.

原子质量也是如此。 我们以原子质量单位测量原子质量。

Today, we learned about two of the most important units of measure in chemistry, atomic mass units and moles.

今天，我们了解了化学中两个最重要的计量单位， 原子质量单位和摩尔。

That means that the nucleus of a helium atom has 0.030377 unified atomic mass units less mass than its component parts.

这意味着氦原子核的质量比其组成部分少 0.030377 个统一原子质量单位。

And each proton has an atomic mass of one, in atomic mass units, and each neutron has an atomic mass of one atomic mass unit.

每个质子的原子质量为一，以原子质量单位表示，每个中子的原子质量为一个原子质量单位。

So the products of this reaction always have less total mass – as measured in unified atomic mass units – than the parent nucleus has.

因此，该反应的产物总质量（以统一原子质量单位衡量）总是小于母核。

But two neutrons and two protons – the component parts of a helium atom – taken together have a mass of 4.032980 unified atomic mass units.

但是两个中子和两个质子——氦原子的组成部分——加在一起的质量为 4.032980 个统一原子质量单位。

So most of the carbon you'll find-- if you just found carbon someplace, on average its weight in atomic mass units is going to be 12.0107.

所以你会发现大部分的碳——如果你只是在某个地方发现碳，平均而言，它的原子质量单位重量将为 12.0107。

Specifically the mass of the nucleus, exactly 15.99 atomic mass units, is lower than the mass of its individual nucleons put together, in this case 16.13 amu's.

具体来说，原子核的质量恰好是 15. 99 个原子质量单位，低于其单个核子的质量总和， 在本例中为 16. 13 amu。