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Valence Electrons

  • Last Updated : 02 Mar, 2022

Any of the fundamental negatively charged particles in the outermost area of atoms that participate in the creation of chemical bonds are referred to as valence electrons. Changes in the atomic structure are confined to the outermost, or valence, electrons regardless of the kind of chemical connection (ionic, covalent, or metallic) between atoms. They are less strongly attracted to the positive atomic nucleus than the inner electrons and can thus be shared or transferred during the bonding process with nearby atoms. In metals and semiconductors, valence electrons are also involved in the conduction of electric current.

What Are Valence Electrons?

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. 

Because valence electrons have higher energy than electrons in inner orbits, they are involved in the majority of chemical processes. They assist us in determining the chemical properties of an element, such as its valency or how it forms bonds with other elements. It also tells us how easily atoms can make bonds, how many unpaired electrons there are, and how many atoms may participate.

Characteristics of Valence Electrons:

Electrons are believed to occupy orbitals in an atom and are important in chemical bonding. Atoms are most stable when they have completed their octet, which can be accomplished through electron transfer or sharing. The following are some of the most important qualities of a valence electron:

  1. The valence electron exists exclusively in the outermost electron shell of the main group elements.
  2. In the inner shell of a transition metal, a valence electron can exist.
  3. Chemically, an atom with a closed shell of valence electrons is usually inert.
  4. The electrical conductivity of an element is also determined by its valence electrons. A metal, a non-metal, or a metalloid, depending on the nature of the elements.

Determination of Valence Electrons:

The number of valence electrons in neutral atoms is equal to the atom’s main group number.

Number of valence electrons = Main group number (neutral atoms)

The main group number of an element can be found in its periodic table column. Carbon, for instance, belongs to group 4 and has four valence electrons. Oxygen belongs to group 6 and has a valence electron count of 6.

Electron Dot Diagrams

An electron dot diagram is a representation of an atom’s valence electrons that employs dots to surround the element’s symbol. The number of dots corresponds to the atom’s valence electrons. With no more than two dots on each side, these dots are positioned to the right and left, above and below the symbol.

How to Draw Electron Dot Diagram?

The steps that must be followed while drawing a Lewis structure are listed below.

  1. To begin, add the individual valencies of each atom to get the total amount of valence electrons in the molecule.
  2. If the molecule is an anion, extra electrons (Number of electrons added = magnitude of negative charge) are added to the Lewis dot structure.
  3. When considering cationic compounds, electrons are removed from the overall count to compensate for the positive charge.
  4. The molecule’s or ion’s core atom is comprised of the least electronegative atom.
  5. Single bonds are now used to connect the atoms.
  6. 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.
  7. 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.
  8. To meet the octet rule for two atoms, a lone pair can be changed into a bond pair if necessary.

Electron Dot Diagram of CO2

  1. The valence shell of an oxygen atom includes six electrons.
  2. Four of the valence electrons are in lone pairs, meaning that in order to achieve an octet configuration, the oxygen atom must engage in two single bonds or one double bond.
  3. Because an O2 molecule has just two oxygen atoms, the atoms form a double bond, resulting in the Lewis electron dot structure shown below.

Electron Dot Diagram of CO2

Finding Valence Electrons for All Elements Except Transition Metals

Each of the periodic table’s squares. Determine the atomic number, group, and a periodic number of oxygen, for example. Elements with comparable chemical characteristics are grouped together in the periodic table. The number of electron shells possessed by atoms of the elements in that row is measured in periods. Period 2 and Group 16 include oxygen. 

The following rule should be used: If an element is not a transition metal, the number of valence electrons increases as the period progresses from left to right. With one valence electron, a new period begins. According to this rule, group 1 elements have one valence electron, group 2 elements have two valence electrons, group 13 elements have three valence electrons, group 14 elements have four valence electrons, and so on.

Valence Electrons and Reactivity

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.

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.

To create their link, nonmetals must attract electrons towards themselves. It may share electrons with an adjacent atom to make a covalent bond, or it could take one electron away to form an ionic bond. As a result, halogens are the most reactive nonmetals, as they only require one electron to form bonds. To create a covalent link, they either remove an electron from another atom or share an electron from another storm. Because the valence electrons are at progressively higher energies in groups, the nonmetal’s reactivity reduces because the atoms are unable to gain stability by obtaining electrons.

Valency

An atom’s electrons are grouped in distinct orbits. According to the Bohr-Bury system, an atom’s outermost shell can hold up to 8 electrons. Furthermore, atoms with a totally filled outermost shell have little chemical activity, implying that their valency is zero. It also indicates that they are inactive substances. Helium has two electrons in its outermost shell, while the other inert elements have atoms with eight electrons in their outermost shells. An octet is defined as an outermost shell with eight electrons. As a result, atoms would react to form an octet in the outermost shell. By sharing, gaining, or losing electrons, the octet is formed. The valency of an element is determined by the number of electrons acquired, lost, or shared to complete the octet in the outermost shell.

Examples of Valency:

  1. 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.
  2. Magnesium (Mg) and aluminium (Al) have two and three electrons in their outermost shells, respectively, giving them a valency of two and three.
  3. 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.
  4. Likewise, it is two for oxygen (O) (subtracting six from eight).

Valence electrons in the first thirty elements are given below-

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

Sample Questions 

Question 1: Why do elements want to complete their octet?

Solution:

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.

Question 2: Find out the valency of Hydrogen, Magnesium and Aluminum. 

Solution:

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.

Question 3: By following methods of the previous question, the valency of Oxygen comes out be six but it is two. Why? 

Solution:

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.

Question 4: What is the relation between metallic elements and their reactivity?

Solution:

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.

Question 5: What is the role of Valence Electrons in Bond Formation? 

Solution:

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.


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