135 化学元素的原子质量
Atomic Mass of Chemical Elements
（https://www.nuclear-power.com/）
化学元素的原子质量
The atomic mass is the mass of an atom. The atomic mass or relative isotopic mass refers to the mass of a single particle, and therefore is tied to a certain specific isotope of an element. The atomic mass is carried by the atomic nucleus, which occupies only about 10-12 of the total volume of the atom or less, but it contains all the positive charge and at least 99.95% of the total mass of the atom. Note that, each element may contain more isotopes, therefore this resulting atomic mass is calculated from naturally-occuring isotopes and their abundance.
原子质量是一个原子的质量。原子质量或相对同位素质量是指单个粒子的质量，因此与一种元素的特定同位素有关。原子质量是由原子核携带的，它只占原子总体积的10^-12或更少，但它包含所有的正电荷和至少占原子总质量的99.95%。请注意，每个元素可能包含更多的同位素，因此由此产生的原子质量是根据天然产生的同位素及其丰度计算的。
The size and mass of atoms are so small that the use of normal measuring units, while possible, is often inconvenient. Units of measure have been defined for mass and energy on the atomic scale to make measurements more convenient to express. The unit of measure for mass is the atomic mass unit (amu). One atomic mass unit is equal to 1.66 x 10-24 grams. One unified atomic mass unit is approximately the mass of one nucleon (either a single proton or neutron) and is numerically equivalent to 1 g/mol.
原子的大小和质量是如此之小，以致于标准的测量单位虽然可能，但常常是不方便的。原子尺度上的质量和能量的度量单位已经确定使得测量更方便地表达。质量的度量单位是原子质量单位（amu）。一个原子质量单位等于1.66x10^-24克。一个统一的原子质量单位大约是一个核子（单个质子或中子）的质量，在数值上相当于1g /mol。
For 12C the atomic mass is exactly 12u, since the atomic mass unit is defined from it. For other isotopes, the isotopic mass usually differs and is usually within 0.1 u of the mass number. For example, 63Cu (29 protons and 34 neutrons) has a mass number of 63 and an isotopic mass in its nuclear ground state is 62.91367 u.
对于12C，原子质量正好是12u，因为原子质量的单位是由其定义的。同位素质量通常与其他同位素不同，相差通常在0.1 u以内。例如，63Cu（29个质子和34个中子）的质量数为63，其核基态的同位素质量为62.91367 u。
（待续）