127 原子质量数
Atomic Mass Number
（https://www.nuclear-power.com/）
原子质量数
The atomic mass number is the total number of protons and neutrons in the nucleus of an atom and is given the symbol A. The atomic mass number determines especially the atomic mass of atoms.
原子质量数是原子核中质子和中子的总数，用符号A表示。原子质量数特别决定了原子的原子质量。
The atom consists of a small but massive nucleus surrounded by a cloud of rapidly moving electrons. The nucleus is composed of protons and neutrons. The total number of protons and neutrons in the nucleus of an atom is called the atomic mass number (or the mass number) of the atom and is given the symbol A.
原子由一个小而重的原子核组成，原子核周围环绕着一团快速移动的电子。原子核是由质子和中子组成的。原子核中质子和中子的总数称为原子质量数（或质量数），用符号A表示。
Neutron number plus atomic number equal atomic mass number: N Z=A. The difference between the neutron number and the atomic number is known as the neutron excess: D = N – Z = A – 2Z.
中子数加上原子序数等于原子质量数：N Z=A。中子数和原子序数之间的差异被称为中子过剩：D = N - Z = A - 2Z。
The atom’s chemical properties are determined by the number of protons and the number and arrangement of electrons. The configuration of these electrons follows the principles of quantum mechanics. The number of electrons in each element’s electron shells, particularly the outermost valence shell, is the primary factor determining its chemical bonding behavior. In the periodic table, the elements are listed to increase the atomic number Z.
原子的化学性质是由质子数量、电子数量及其排列决定的。这些电子的配置遵循量子力学的原理。每个元素的电子层，特别是最外层的价电子层中的电子数是决定其化学键行为的主要因素。在元素周期表中，元素按原子序数Z增序排列。
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