价电子
参与化学键生成的原子最外层区域中的任何基本带负电粒子都称为价电子。原子结构的变化仅限于最外层的电子或价电子,而不管原子之间的化学连接类型(离子、共价或金属)如何。与内部电子相比,它们对正原子核的吸引力较小,因此可以在与附近原子的键合过程中共享或转移。在金属和半导体中,价电子也参与电流的传导。
什么是价电子?
The number of electrons an atom needs loses or gain to reach the octet or ensure stability is known as valence. Valence electrons are electrons in the outer shells that are not filled.
由于价电子比内轨道中的电子具有更高的能量,因此它们参与了大多数化学过程。它们帮助我们确定元素的化学性质,例如它的化合价或它如何与其他元素形成键。它还告诉我们原子形成键的难易程度,有多少未配对的电子,以及有多少原子可以参与。
价电子的特性:
电子被认为占据原子中的轨道并且在化学键合中很重要。原子在完成八位字节时最稳定,这可以通过电子转移或共享来完成。以下是价电子的一些最重要的品质:
- 价电子只存在于主族元素的最外层电子壳层中。
- 在过渡金属的内壳中,可以存在价电子。
- 在化学上,具有闭合价电子壳的原子通常是惰性的。
- 元素的电导率也由其价电子决定。金属、非金属或准金属,取决于元素的性质。
价电子的测定:
中性原子中的价电子数等于原子的主族数。
Number of valence electrons = Main group number (neutral atoms)
元素的主族编号可以在其元素周期表列中找到。例如,碳属于第 4 族,具有四个价电子。氧属于第 6 族,价电子数为 6。
电子点图
电子点图是原子价电子的表示,它使用点围绕元素的符号。点的数量对应于原子的价电子。每边不超过两个点,这些点位于符号的左右、上方和下方。
How to Draw Electron Dot Diagram?
The steps that must be followed while drawing a Lewis structure are listed below.
- To begin, add the individual valencies of each atom to get the total amount of valence electrons in the molecule.
- If the molecule is an anion, extra electrons (Number of electrons added = magnitude of negative charge) are added to the Lewis dot structure.
- When considering cationic compounds, electrons are removed from the overall count to compensate for the positive charge.
- The molecule’s or ion’s core atom is comprised of the least electronegative atom.
- Single bonds are now used to connect the atoms.
- Each atom in the molecule now has a lone pair of electrons assigned to it. The most electronegative atoms are usually assigned the lone pairs first.
- If every atom does not have an octet configuration after the lone pairs have been allocated, a double or triple bond must be drawn to fulfill the octet valency of each atom.
- To meet the octet rule for two atoms, a lone pair can be changed into a bond pair if necessary.
CO 2的电子点图
- 氧原子的价壳层包括六个电子。
- 四个价电子是孤对电子,这意味着为了实现八位组构型,氧原子必须参与两个单键或一个双键。
- 因为 O 2分子只有两个氧原子,所以原子形成双键,形成如下所示的路易斯电子点结构。
寻找除过渡金属以外的所有元素的价电子
每个元素周期表的正方形。例如,确定氧的原子序数、基团和周期数。具有可比化学特性的元素在元素周期表中被归为一组。该行中元素的原子所拥有的电子壳层数以周期为单位测量。第 2 期和第 16 组包括氧气。
应该使用以下规则:如果元素不是过渡金属,则价电子数随着周期从左到右的进展而增加。有了一个价电子,一个新的时期就开始了。根据这个规则,第 1 族元素有 1 个价电子,第 2 族元素有 2 个价电子,第 13 族元素有 3 个价电子,第 14 族元素有 4 个价电子,以此类推。
价电子和反应性
最活泼的金属元素,如钠和钾,位于第 1 族。因此,第 1 族元素具有单价壳层电子,这些电子很容易失去以产生正离子。结果,它只有一个电子可以失去,使其更容易连接和更具反应性。因为第 2 族的金属在其价壳层中有两个价电子,所以它们必须失去两个价电子才能产生正金属离子。失去两个电子比失去一个更难。因此,它们的反应性较低,并且这些金属比第 1 组元素更耐用。
The reactivity of metals tends to grow as they progress through each group. As the valence electrons become less bonded to the nucleus, they will be more easily withdrawn, and as the number of shells grows by one down the group, the atomic size will increase as well.
为了建立它们的联系,非金属必须将电子吸引到自己身上。它可以与相邻原子共享电子以形成共价键,也可以带走一个电子以形成离子键。因此,卤素是最具反应性的非金属,因为它们只需要一个电子即可形成键。为了创建共价链接,它们要么从另一个原子中移除一个电子,要么从另一个风暴中共享一个电子。由于价电子在基团中的能量越来越高,因此非金属的反应性降低,因为原子无法通过获得电子来获得稳定性。
价
原子的电子被分组在不同的轨道上。根据 Bohr-Bury 系统,原子的最外层可以容纳多达 8 个电子。此外,具有完全填充的最外壳的原子几乎没有化学活性,这意味着它们的化合价为零。这也表明它们是非活性物质。氦的最外层有两个电子,而其他惰性元素的最外层有八个电子的原子。八位组被定义为具有八个电子的最外层。结果,原子会发生反应,在最外层形成一个八位字节。通过共享、获得或失去电子,形成八位字节。元素的化合价取决于为完成最外层的八位字节而获得、丢失或共享的电子数。
效价的例子:
- 最外层的氢 (H)、锂 (Li) 和钠 (Na) 原子均具有一个电子。结果,它们中的每一个都有可能失去一个电子。结果,它们的化合价为一。
- 镁 (Mg) 和铝 (Al) 在它们的最外层壳中分别有两个和三个电子,使它们的化合价为 2 和 3。
- 当原子最外层电子的数量接近其最大容量时,化合价的决定不同。氟(F)原子的最外层有七个电子,它的化合价可能是七个,但它得到一个电子比失去七个更容易。结果,它的化合价为一。它是通过从八位字节中取出七个电子制成的。
- 同样,氧气 (O) 为 2(从 8 中减去 6)。
前三十个元素中的价电子如下 - Atomic Number Element Valence Electrons 1 Hydrogen (H) 1 2 Helium (He) 2 3 Lithium (Li) 1 4 Beryllium (Be) 2 5 Boron (B) 3 6 Carbon (C) 4 7 Nitrogen (N) 5 8 Oxygen (O) 6 9 Fluorine (F) 7 10 Neon (Ne) 8 11 Sodium (Na) 1 12 Magnesium (Mg) 2 13 Aluminium (Al) 3 14 Silicon (Si) 4 15 Phosphorus (P) 5 16 Sulphur (S) 6 17 Chlorine (Cl) 7 18 Argon (Ar) 8 19 Potassium (K) 1 20 Calcium (Ca) 2 21 Scandium (Sc) 2 22 Titanium (Ti) 2 23 Vanadium (V) 2 24 Chromium (Cr) 1 25 Manganese (Mn) 2 26 Iron (Fe) 2 27 Cobalt (Co) 2 28 Nickel (Ni) 2 29 Copper (Cu) 1 30 Zinc (Zn) 2
示例问题
问题 1:为什么元素要完成它们的八位字节?
解决方案:
Atoms of elements, having a completely filled outermost shell show little chemical activity which means that their valency is zero. It also means that they are inert elements which makes them stable and less prone to reactions. Helium has two electrons in its outermost shell and all other elements have atoms with eight electrons in the outermost shell. An outermost-shell which has eight electrons is said to possess an octet. Atoms react to achieve an octet in the outermost shell. The octet can be achieved by sharing, gaining or losing electrons. The number of electrons gained, lost or shared to complete the octet in the outermost shell, gives us valency of the element.
问题2:找出氢、镁和铝的化合价。
解决方案:
The outermost shell of hydrogen (H), lithium (Li), and sodium (Na) atoms all have one electron. As a result, each of them has the potential to lose one electron. As a result, they have a valency of one.
Magnesium (Mg) and aluminium (Al) have two and three electrons in their outermost shells, respectively, giving them a valency of two and three.
问题3:按照上一个问题的方法,氧的化合价是六,但它是二。为什么?
解决方案:
When the number of electrons in an atom’s outermost shell approaches its maximum capacity, valency is decided differently. The outermost shell of the fluorine (F) atom possesses seven electrons, and its valency might be seven, but it is easier for it to gain one electron than to lose seven. As a result, its valency is one. It’s made by taking seven electrons out of the octet.
问题4:金属元素与它们的反应性有什么关系?
解决方案:
The most reactive metallic elements, such as sodium and potassium, are found in group 1. As a result, group 1 elements have single valence shell electrons that can readily be lost to produce a positive ion. As a result, it only has one electron to lose, making it easier to connect and more reactive. Because the metals in group 2 have two valence electrons in their valence shell, they must lose two valence electrons to produce a positive metal ion. Losing two electrons is more difficult than losing one. As a result, they are less reactive, and these metals are more durable than group 1 elements.
问题 5:价电子在成键中的作用是什么?
解决方案:
Valence electrons help chemical bonding. If an element lacks a valence electron or is in the octet state (Noble gases), it will not form bonds unless it is given enough energy to break the electrons out of the octet state and bond. The valence electrons of one element combine with the valence electrons of another element to form a chemical bond.