分子量

古印度和古希腊的哲学家首先给出了原子的概念并对其进行了深入研究。公元前500年左右。印度哲学家 Maharishi Kanad 指出，如果我们划分“Padarth”（物质），我们会得到小颗粒。最后，粒子的进一步划分是不可能的，他将那个粒子命名为“Parmanu”。

大约在同一时代，古希腊哲学家德谟克利特和留基普斯提出，如果我们继续分割物质，那么得到的粒子将无法进一步分割。他们把这些不可分割的粒子称为原子（意思是不可分割的）。所有这一切都只是理论，而不是实际或实验的考虑。到 18 世纪末，科学家们进行了更多的搜索并了解了化合物和元素之间的差异，这引起了人们对找出它们如何结合、为什么结合以及之后发生什么的兴趣。 Antoine L. Lavoisier 进一步研究化学组合的规律。

周围的一切都是由非常小的单位组成的，这些单位在科学语言中是原子，在0.1-0.5纳米的范围内非常小。

什么是分子？

A molecule is a group of two or more atoms that are chemically bonded together, i.e, tightly held together by attractive forces. A molecule can be defined as the tiniest particle of an element or a compound that is fit for a free existence and shows all the properties of its parent substance.

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相同或不同元素的原子可以形成分子。以下是一些重要分子的列表，它们的组合比和质量比为：

Compound	Combining Elements	Ratio of Elements by Mass
Water	Hydrogen & Oxygen	1:8
Ammonia	Nitrogen & Hydrogen	14:3
Carbon Dioxide	Carbon & Oxygen	3:8

鼹鼠概念

It is easier to use the quantity of substance in a number of molecules or atoms instead of their mass, so the unit called Mole is used.

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如果元素被称重并且它等于其以克为单位的原子量，那么它包含一定量的元素，这代表一摩尔元素，并且该一定量的元素是6.022 x 10 ²³个元素的原子。 1摩尔任何分子或原子等于其原子质量或以克为单位的分子量。 1 摩尔中的粒子数 = 6.022 x 10 ²³个原子或分子，这被称为Avagadro 数。

1摩尔中的粒子数：

1 摩尔氢原子显示 6.022 × 10 ²³个氢原子。
1摩尔氢分子显示6.022×10 ²³个氢分子。
1 摩尔水分子显示 6.022 × 10 ²³个水分子。

在数学上，摩尔数定义为：

摩尔数 (n) = 给定物质的质量 / 分子的摩尔质量

或者

摩尔数 (n) = 给定粒子数 (N) / 阿伏伽德罗数 (N ₀ )

现在让我们通过解决一个例子来理解上述公式，

例 1：求 24.088 ×10 ²³个水粒子内的摩尔数。

回答：

Given that,

The number of particles present, N = 24.088 ×10²³

The number of moles (n) = Number of particles (N) / Avogadro number (N₀)

= 24.088 ×10²³ / 6.022 x 10²³

= 4 moles

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分子量

The molecular mass of an element is defined as the sum of all the masses of the elements present inside the molecule. e.g. the molecular mass of water, in which there are two hydrogen atoms and one oxygen atom present, is 18 (i.e. 2 + 16). Also called its molecular weight.

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分子质量是通过将原子数乘以分子中元素的原子质量，然后将分子中所有元素的质量相加来预测的。下表显示了元素周期表中前 20 个元素的原子质量：

Atomic number	Name	Symbol	Atomic Weight (in a.m.u.)
1	Hydrogen	H	1.00979
2	Helium	He	4.00260
3	Lithium	Li	6.941
4	Beryllium	Be	9.01218
5	Boron	B	10.81
6	Carbon	C	12.011
7	Nitrogen	N	14.0067
8	Oxygen	O	15.9994
9	Fluorine	F	18.998403
10	Neon	Ne	20.179
11	Sodium	Na	22.98977
12	Magnesium	Mg	24.305
13	Aluminium	Al	26.98154
14	Silicon	Si	28.0855
15	Phosphorus	P	30.97376
16	Sulphur	S	32.06
17	Chlorine	Cl	35.453
18	Argon	Ar	39.0983
19	Potassium	K	39.948
20	Calcium	Ca	40.08

What are Ions?

It is an electrically charged species or atom or group of atoms. It is formed by either gaining or losing one or more electrons by an atom.

Ions are of two types:

Cation

Cations are formed by the loss of one or more electrons from an atom, so they are positively charged ions. e.g.

On losing one electron sodium atom forms a sodium ion Na as,

Na – e⁻ → Na⁺

On losing two electrons Magnesium forms a magnesium ion as,

Mg – e^– → Mg⁺

Again it loses one more electron to complete its octet as,

Mg⁺ – e^– → Mg²⁺

Anion

It is a negatively charged ion and is formed by the gain of one or more electrons by an atom. e.g.

On gaining one electron chlorine form a chloride ion Cl⁻ as,

Cl + e⁻ → Cl⁻

On gaining two electrons oxygen form an oxide ion as,

O + e^– → O^–

Again it gains one more electron to complete its octet as,

O^– + e- → O^2-

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分子质量的计算

分子质量是通过将原子数乘以分子中元素的原子质量，然后将分子中所有元素的质量相加来预测的。

确保分析化学式以确定化合物中每个元素的原子数。
将化合物中存在的原子数乘以每个元素的原子量。
将所有质量相加并将其单位指定为克/摩尔。

示例 2：确定 CO ₂的摩尔质量。

回答：

First Calculate the number of each atom, and assign their atomic weight individually

The number of carbon atoms × its atomic mass: 1 × 12 = 12

The number of oxygen atoms × its atomic mass: 2 × 12 = 24

Then add the values i.e, 12 + 24= 36

Therefore the molar mass of CO₂ is 36 g/mol.

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例3：确定CaCl ₂的公式单位质量。

回答：

The formula unit mass of CaCl₂ = Atomic mass of Ca + 2 × (Atomic mass of Cl)

= 40 + 2 × 35.5

= 40 + 71

= 111 a.m.u.

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示例问题

问题1：什么是原子性？列出元素周期表中不同主要元素的原子性。

回答：

Atomicity is defined as the number of atoms present in one molecule of an element or a compound is known as its atomicity. below is the table that shows the atomicity.

Name of the Element	Atomicity
Argon	Monoatomic
Helium	Monoatomic
Oxygen	Diatomic
Hydrogen	Diatomic
Nitrogen	Diatomic
Chlorine	Diatomic
Phosphorus	Tetra-atomic
Sulphur	Poly-atomic

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问题 2：碳酸钠 Na ₂ CO ₃的摩尔质量是多少？

回答：

Since, a molecule of sodium carbonate contains two atoms of sodium (Na), one atom of carbon (C) and three atoms of oxygen (O). The molecular weight would be

Na: 2 × 23.0 g = 46 g

C: 1 × 12.0 g = 12 g

O: 3 × 16 g = 48 g

When we add up the total values i.e, 46 g + 12 g + 48 g = 106 g

Hence, the molar mass of Na₂CO₃ is 106 g/mole.

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问题3：计算H ₂ SO ₄的摩尔质量。

回答：

The molar mass can be calculated as:

Molar mass of H₂SO₄ = (2 × Mass of Hydrogen) + (1 × Mass of Sulphur) + (4 × Mass of Oxygen)

= (2 × 1 + 1 × 32 + 4 × 16) g/mol

= (2 + 32 + 64) g/mol

= 98 g/mol

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问题 4：说出 1 克氢气中的氢 (H) 原子数。

回答：

Since one gram of Hydrogen (H) contains 1 mole of Hydrogen which is equal to 6.022 x 10²³atoms.

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问题 5：有多少原子存在于：

(a) H ₂ S 分子和

(b) PO ₄ ^-3离子？

回答：

(a) In H₂S, there is one sulphur and two hydrogen atoms present so a total of 3 atoms are present.

(b) In PO₄⁻³, one Phosphorus and 4 oxygen atoms are present so a total of 5 atoms are present.

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问题6：什么是质量：

(a) 1 摩尔氮原子？

(b) 4 摩尔铝 (Al) 原子（原子质量 Al=27）？

(c) 20 摩尔亚硫酸钠 (Na ₂ SO ₃ )？

回答：

(a) 1 mole of Nitrogen = 1 × Atomic mass of nitrogen atom

= 1 × 14 g

= 14 g

(b) 4 moles of aluminium atoms = 4 × Atomic mass of aluminium atom

= 4 × 27 g

= 108 g

(c) 20 moles of sodium sulphite (Na₂SO₃) = 20 (2 × Atomic mass of Na + 1 × Atomic mass of sulphur + 3 × Atomic mass of oxygen)

= 20 (2 × 23 g+1 × 32 g + 3 × 16 g)

= 20 (46 g + 32 g + 48 g)

= 20 × 126 g

= 2520 g

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