原子序数和质量数
原子的结构包括提供原子质量和电荷的质子、中子和电子。原子核由质子和中子组成，电子围绕它们运行。因为原子是电中性的，所以带正电的质子和带负电的电子的数量必须相同。此外，由于中子对电荷没有影响，它们的数量与质子的数量无关，即使在相同元素的原子之间也可能不同。
在了解元素的原子序数和质量数的概念之前，让我们讨论原子的三个主要基本粒子：
- Electrons: Electrons are the negatively charged sub-atomic particles of an atom. The mass of an electron is negligible. The symbol for an electron is e–. Electrons are extremely small and are found outside the nucleus.
- Protons: Protons are the positively charged particles that are present in the nucleus of a hydrogen atom, that is protons are the positively charged sub-atomic particles of an atom. The mass of a proton is negligible. The symbol for an electron is p+. Electrons are extremely small and are found outside the nucleus.
- Neutrons: Neutrons are subatomic particles that are one of the primary constituents of atomic nuclei. Neutrons are denoted by n or no. Neutrons don’t have any charge associated with them. They have a mass that is slightly greater than that of a proton. Neutrons and protons are collectively called nucleons.
以下是电子、质子和中子的一些重要性质： Particle Charge Mass of the particle Symbol Location in an atom Electron -1.6 × 10-19 Coulomb 9.11 × 10-31 kg e– Outside the nucleus Proton +1.6 × 10-19 Coulomb 1.673 × 10-27 kg p+ In the nucleus Neutron No charge 1.675 * 10-27 kg n or no In the nucleus
原子数
The number of protons that a chemical element has in its centre (nucleus) is called the atomic number. The mass number is determined by the number of protons and neutrons combined.
原子序数和质量数总是整数，因为它们是通过计算质子、中子和电子而获得的。原子的质量数和原子序数之和对应于原子中存在的亚原子粒子的总数。
在数学上，原子序数定义为。
原子序数 (Z) = 质子数 (p + )
质量数以原子质量单位 (amu) 报告原子核的质量。
原子序数的性质：
- 原子核中的质子总数为我们提供了原子的原子序数。
- 它用字母“Z”表示。
- 不同元素的原子具有不同的原子序数。例如，所有碳原子的原子序数都是 6，而所有氧原子的原子序数都是 8。
- 这个术语是由亨利·格温-杰弗里斯·莫斯利首先提出的。
质量数
Rutherford discovered that an atom’s nucleus, which is made up of protons and neutrons, contains the vast bulk of its mass. The total number of protons and neutrons in an atom is known as the mass number.
质量数的属性：
- 质子和中子的数量加起来就是原子的质量数。
- 它用字母“A”表示。例如，一个碳原子有 6 个质子和 6 个中子。因此，它的质量数是 12。
- 虽然质子的数量在元素的所有原子中保持不变，但中子的数量可以变化。因此，相同元素的原子可以有不同的质量数，这些被称为同位素。
在数学上，质量数定义为。
质量数 (A) = 质子数 + 中子数
元素周期表中不同元素的质量数和原子序数如下： Element Symbol Atomic Number (Z) Mass Number (A) Number of Protons Number of Electrons Number of Neutrons (A-Z) Valency Hydrogen H 1 1 1 1 0 ±1 Helium He 2 4 2 2 2 0 Lithium Li 3 7 3 3 4 +1 Beryllium Be 4 9 4 4 5 +2 Boron B 5 11 5 5 6 +3 Carbon C 6 12 6 6 6 +4 Nitrogen N 7 14 7 7 7 -3 Oxygen O 8 16 8 8 8 -2 Fluorine F 9 19 9 9 10 -1 Neon Ne 10 20 10 10 10 0 Sodium Na 11 23 11 11 12 +1 Magnesium Mg 12 24 12 12 12 +2 Aluminium Al 13 27 13 13 14 +3 Silicon Si 14 28 14 14 14 +4 Phosphorus P 15 31 15 15 16 -3 Sulphur S 16 32 16 16 16 -2 Chlorine Cl 17 35 17 17 18 -1 Argon Ar 18 40 18 18 22 0 Potassium K 19 39 19 19 20 +1 Calcium Ca 20 40 20 20 20 +2
化合价及其与原子序数（A）和质量数（Z）的区别
- 存在于原子最外层的电子称为价电子，它们与相同或不同元素的原子反应并形成分子的结合能力称为原子的化合价。
- 具有完全填充的最外壳的元素原子显示出很少的化学活性，并且它们的结合容量或化合价为零。
- 例如，氢的最外层电子数为1，镁为2。因此，氢的化合价为1，因为它很容易失去1个电子而变得稳定。另一方面，镁是2，因为它很容易失去2个电子并获得稳定性。
- 当我们想找出化合价时，我们会查看最外层的电子，但当我们想知道原子序数或质量数时，我们会查看质子和中子的总数。
示例问题
问题1：定义原子序数和质量数。
回答：
The number of protons that a chemical element has in its centre (nucleus) is called atomic number.
Atomic Number (Z) = No of protons
The mass number is determined by the number of protons and neutrons combined.
Mass Number (A) = No of Protons + No of Neutrons
问题2：为什么原子序数和质量数都是整数？
回答：
Atomic number and mass number are always whole numbers as they are obtained by counting protons, neutrons, and electrons. The sum of the mass number and the atomic number for an atom corresponds to the total number of subatomic particles present in the atom.
问题3：为什么用Z表示原子序数？
回答：
The atomic number symbol, Z, stands for “Zahl,” meaning German number. The symbol Z denoted an element’s place in the periodic table before 1915.
问题4：原子的化合价是多少？
回答：
The electrons present in the outermost shell of an atom are known as the valence electrons and its combining capacity to react and form molecules with atoms of the same or different elements is known as valency of the atom.
问题5：化合价和质量数有什么区别？
回答：
When we want to find out the valency, we look at electrons in the outermost shell but when we want to know the atomic number or the mass number, we look at the total number of protons and neutrons.