电价和共价的区别
我们都熟悉原子中的电子是如何组织成轨道或壳层的。价电子是存在于原子最外层轨道上的电子。根据 Bohr-bury 理论,最外层最多可以容纳 8 个电子。当最外壳被完全填满时,几乎没有化学活性。它的结合能力同样降低到零。
例如,氮与氢形成多种化合物,包括 NH 3 、N 2 H 4和 N 3 H,其中氮原子的化合价分别为 3、2 和 1/3。结果,将化合价作为一个单一数字的想法仍然不清楚。结果,化合价最终被定义为分子中原子建立的化学键的数量。
价
The combining capacity of an atom in an element with the atom of the same or another element is known as valency. Valency generally represents the outermost electrons in the valency shell.
原子的最外层称为价层,而存在于最外层或价层中的电子称为价电子。由于化合价被定义为原子的结合能力,因此结合能力是根据原子获得、失去、共享的电子数来确定的。
电子总是试图通过在价壳层中获得8个电子来获得稳定的电子构型,因此它们不断地试图与相同或不同元素的原子形成键。化合价是根据参与形成键的电子数确定的。
让我们研究元素周期表中前 10 个元素的化合价: Atomic Number Element and its Symbol Valency 1 Hydrogen (H) 1 2 Helium (He) 0 3 Lithium (Li) 1 4 Beryllium (Be) 2 5 Boron (B) 3 6 Carbon (C) 4 7 Nitrogen (N) 3 8 Oxygen (O) 2 9 Fluorine (F) 1 10 Neon (Ne) 0
很少有元素显示可变化合价,因为有时这些元素在某些不同条件下与其他元素结合时,同一元素的化合价会发生变化。
什么是可变价?
当与不同元素反应时,在不同条件下显示不同化合价的元素这种性质称为可变化合价。这种性质表现在那些电子从倒数第二层失去以使原子稳定的元素中。大多数 d 嵌段元素倾向于显示可变化合价。
Examples of variable valency are,
- Iron shows variable valency as 2 and 3.
- Manganese shows variable valency as 2, 4, and 7.
- Copper shows variable valency as 1 and 2.
如何确定元素的化合价?
我们可以通过简单地知道元素在元素周期表中的位置来确定元素的化合价,因为它们是根据原子序数排列的。为了确定元素的化合价,其中涉及不同的步骤,它们是:
- 找到元素化合价的第一步是写出相应的元素电子配置,并确定每个壳层中的电子数,尤其是最后一层壳层中的电子数。
- 在确定最后一层中的电子数后,如果电子数小于或等于四,则该特定元素的化合价将等于最后一层中的电子数,因为化合价被定义为结合元素的容量为了变得稳定,该特定元素将失去这些电子,因此具有等于价壳电子数量的化合价。
- 如果化合价电子大于 4,则电子的化合价将等于 8 与化合价壳中电子数之间的差,因为为了变得稳定,原子试图获得八位组构型,因此化合价将等于 8 – (价壳中的电子数)。
让我们通过以下示例来理解上述概念:
示例 1:确定硼的化合价。
解决方案:
The electronic configuration of Boron is: 1s2 2s2 2p1
Number of electrons in valency shell = 3
As a number of outermost shell electrons < 4.
This implies the valency of Boron = number of electrons in the outermost shell
Hence, the valency of Boron = 3.
价的类型
根据两个原子之间使用价电子形成的键,价分为两种类型:电价和共价。让我们深入讨论它们:
1. 电价
The number of electrons lost or gained by atoms of an element in order to form an ionic or electrovalent bond so that atoms achieve the nearest stable configuration or inert gas configuration is known as Electrovalency.
价态被定义为在原子之间建立离子连接的过程中,电子从一个元素的原子转移到另一个元素的原子。在这种转移过程中,原子失去或获得的电荷数也可以用这种方式表示。元素获得电子时电价为负,失去电子时电价为正。
让我们考虑以下示例:
- 氯化钠(NaCl):钠和氯原子形成离子键,钠失去一个电子得到最近的惰性气体构型,即得到氖气构型,氯得到一个电子并变得稳定。在这里,由于钠失去一个电子,其电价为 1,而氯获得一个电子,其电价为 1。Na 将具有正电价,而 cl 将具有负电价。
- 氯化镁(MgCl 2 ):镁和氯原子形成离子键,镁失去两个电子得到最近的电子构型,即得到氖气构型,每个氯原子得到一个电子并变得稳定。在这里,由于镁失去两个电子,它的正电价为 2,而氯获得一个电子,它的负电价为 1。
2. 共价
The number of electrons shared by two atoms to form a covalent bond so that atoms achieve the nearest stable electronic configuration is known as covalency.
化学物质中电子的共享定义了化合价。它是一个原子可以共享的电子对数。共价键的形成与共价有关。如果原子共享 2 个电子,则参与形成键的原子的共价键为 2。
让我们考虑以下示例:
- 甲烷(CH 4 ):碳和氢之间共享的电子数为4,因此甲烷中碳的共价为4。甲烷中氢的共价为每个氢原子的1。
- 氮分子(N 2 ):这里两个氮原子之间共享的电子数是 3 所以。氮原子的共价键为3。
电价和共价的区别
现在让我们将电价和共价之间的主要区别理解为: Electrovalency CovalencyElectrovalency is defined as the number of electrons lost or gained by an atom to form an ionic bond. Covalency is defined as the number of electrons shared by atoms to form a covalent bond. An ionic bond formation can be explained using Electrovalency A covalent bond formation can be explained using Covalency The electrovalency explains the formation of ionic bonds. However, the covalency of any element leads to the formation of a covalent bond. Ionic or Electrovalent bonds will have electrovalency Covalent bonds will have covalency e.g.: NaCl has electrovalency 1. e.g.: Nitrogen molecule has covalency 3.
示例问题
问题 1:计算铝可以显示的最大共价?
解决方案:
The maximum covalency that can be shown by Aluminium is 6. As Aluminium has vacant d orbitals so the electrons can pair up to 5 electrons here and s and p orbitals have 2 and 1 electrons in them. So, the total sum is 8 as Aluminium cannot have 8 electrons due to its small size its covalency is 6.
问题2:解释可变化合价的原因?
解决方案:
If electrons from the penultimate shells are lost then variable valency is shown in elements. The two main causes of variable valency are differences in energy levels of orbitals and the inert pair effect.
问题3:化合价的符号是什么?
解决方案:
Valency doesn’t show any sign it can neither be positive or negative. By losing or gaining electrons elements will get charge which will have a sign.
问题 4:化合价和氧化数是否相同?
解决方案:
No, valency and oxidation numbers both are different. Valency is defined as combining capacity of an element whereas Oxidation number is defined as the number of electrons lost or gained by an atom while forming a bond. Valency cannot be positive or negative but oxidation numbers can be positive or negative.
问题 5:计算 AlCl 3中铝的电价?
解决方案:
The electrovalency of aluminium in Alcl3 is +3. Here, Aluminium loses 3 electrons and 3 chlorine atoms take an electron each and form an electrovalent bond. Since Aluminium is losing 3 electrons and electrovalency is calculated based on the number of electrons lost or gained by an atom electrovalency of aluminium is +3.
问题 6:s-block 元素是否显示可变化合价?
解决方案:
The s-block elements don’t show variable valency because these elements lose one electron and get stable inert gas configuration and the second ionization potential is very high. Since these elements are stable after losing one electron they don’t show variable valency.
问题 7:哪些元素的化合价为零?
解决方案:
Noble gases have zero valencies because these elements have stable configuration and as valency is defined as combining capacity of an element and Noble gases already have a complete outer shell filled they don’t react with other atoms to become stable.