What are valence electrons and how do you find them?

Date(s) Last Revised: March 30, 2023 by Teachoo

• The name for the collection of electrons in an atom's outermost shell is the electrons that make up valence shells
• And the shell that contains the valence electrons is called the atomic valence shell

Exhibit 1

• Helium possesses 2 electrons.
• Everything is included K Shell (Seeing as the K shell can only accommodate 2 electrons)
• Hence Helium has 2 valence electrons. (because K shell is the last one)
• Therefore, The valence shell is the K shell.

Illustration 2

• 2 Those who hold them K Shell (since the K shell only has room for 2 electrons)
• Remaining 1 is held in L Shell
• Hence Helium has one valence electron. (since L shell is the most outer shell)
• Therefore, The valence shell symbol is "L Shell."

Exhibit 3

• Sodium has 11 electrons.
• 2 holding them in K Shell (Seeing how the K shell can only accommodate 2 electrons)
• 8 of them are imprisoned in L Shell (since the L shell only has room for 8)
• Remaining 1 is held in M Shell
• Hence Sodium has one valence electron. Outermost (as M shell is)
• And The valence shell is M shell.

What's the big deal about valence electrons?

• That is something we are aware of The electrons in the outermost shell are called valence electrons. of an atom
• In chemical reactions, only these electrons are involved.

• Those experiencing their outermost shell full do not react combined with additional components

Example : -

• There are two elements in Helium's outer shell.

• They're all in here K Shell (since the K shell only has room for 2 electrons)

• This means that absence of chemically active free electrons

• The The maximum number of electrons in an atom's outermost (valence) shell is 8. When the number of electrons in a shell is greater than 8, the excess electrons move to the next shell.

• We refer to this as the octet rule

Case in point A calcium atom has 20 electrons.

Remember that only the Only 2 electrons can fit into the K shell. , the Each of the remaining shells has space for 8 electrons. When one shell can no longer hold any more electrons, the remaining electrons will go to the next shell up, and so on.

The structure of its electron shells looks like this:

K shell Two electrons

L shell Eight electrons

M shell Eight electrons

N shell 2-electron valence shell structure.

Despite the fact that the M shell (n = 3) can accommodate 2n 2 = 2 x 3 2 = 18 electrons, or 29

• However, it will be the valence shell in the future. More than 8 electrons would make it too crowded.
• The final 2 e- will be incorporated into the N shell, resulting in a The valence shell will be the N-shell.

Note:- Each atom is most stable when their valence shell contains 8 electrons

Therefore, elements typically bond for the purpose of electron exchange and octet formation.

Examples -

Query from Text

Back Exercises: Q&A 17&18 from the NCERT

Value, what is it?

• The ability of an element to form compounds.

Example:

• Hydrogen has a single valence.
• O2 has a valency of 2.
• Therefore, 1 atom of water (H2O) requires 2 atoms of hydrogen and 1 atom of oxygen to form. 2 O)

How Does One Establish the Valence of an Element?

• Number of elements in outermost shells (valence electrons) determines valency.
• The negative charge of electrons is commonly known.
• The nucleus, a tiny, positively charged center, is what they orbit.
• The nucleus's positive charge cancels out the electrons' negative charge, making the atom electrically neutral.

How do we know what valency an atom has now?

• A valence shell can contain a maximum of 8 electrons.
• Hence, the The valence shell can have anywhere from one to eight electrons.

1. Let's say an atom now has Valence electron count can be one, two, or three.

It is easier for them to drop 1, 2, or 3 e-. octet from their valence to form

    (Since the previous shell contains 8 electrons, it is now its valence shell.)

One electron loss equals one valence.

    Two-electron loss atomic valency equals two

    Atoms that lose three electrons have a valency of 3.

Exhibit 1

• Sodium has 11 electrons in total.

• 2 which are kept in K Shell (since the K shell only has room for 2 electrons)
• 8 of which are kept in L Shell (since there's a cap of 8 electrons in the L Shell)
• Remaining 1 is held in M Shell
• Thus To complete its octet, sodium must lose an electron. Outermost shell with 8 electrons
• Hence, Sodium has a valency of 1.

Exhibit 2

• The number of electrons in magnesium is 12.

• 2 which are kept in K Shell (since the K shell only has room for 2 electrons)
• 8 in which these are kept L Shell (since the L shell only has room for 8)
• Remaining 2 hold court in M Shell
• Thus To complete its octet, magnesium must lose two electrons. Eight electrons make up the valence shell.
• Hence Magnesium has a 2 valence atom.

Second, if an atom has Valence electron count of 5, 6, or 7

It is easier for them to acquire an extra 3, 2, or 1 electron in order to form an octet of the same valence

(Since, after adding one electron each, their valence shells will total eight)

     Atoms that gain one electron have a valency of 1.

Gaining two electrons, or valence, equals two.

Atoms with an extra electron gain a valence of 3.

Illustration 1

• Oxygen has 8 electrons in total.
• 2 which are kept in K Shell (since the K shell only has room for 2 electrons)
• Remaining 6 hold court in L Shell
• Hence Oxygen has 6 valence electrons. (as L shell is outermost shell)
• Thus To complete its octet, oxygen needs to pick up two electrons. Outermost shell with 8 electrons

Hence Oxygen has a 2 valency.

Exhibit 2

• Nitrogen has 7 electrons in total.
• 2 which are kept in K Shell (Seeing how there's a maximum of 2 electrons that can fit in the K Shell)
• Remaining 5 hold court in L Shell
• Hence Nitrogen has 5 valence electrons. (Since L-shell is the last shell in the periodic table)
• Thus The octet state of nitrogen requires the addition of three electrons. Eight electrons in the valence shell
• Hence Nitrogen has a valency of 3.

Third, if a molecule has Its valence shell contains only 4 electrons. then it must have an chance of gaining, losing, or exchanging valence electrons to complete an octet

The valency of these atoms is 4, in any case.

Illustration 3

• Each atom of silicon contains 14 electrons.
• 2 among these are stored in K Shell (because there is a maximum of 2 electrons in the K shell)
• 8 are kept inside L Shell
• Those who are left 4 located in the M shell
• Hence Silicon has 4 valence electrons. because L shell is the most outer shell
• Thus Silicon must either gain four electrons or lose four electrons in order to complete an octet. Eight electrons make up the valence shell.
• Hence, the Silicon has a 4 valency.

Note: - When an atom has Its valence shell contains 8 electrons.

    If so, then has reached octet status and is holding steady

    Hence, it won't give up, pick up, or swap electrons

     Their zero valence

Examples -

Page 52, Question 1 (Q1): Left in Text

Q7: Back Exercise from the Ncert

Why do we need noble gases or inert gases?

• Indeed, it is those elements that do not form compounds with other gases
• These elements all have a valency of 0.

A few examples of noble gases are: -

Element

Quantity of Atoms

Valency

Helium

2

0

Neon

10

0

Argon

18

0

Krypton

36

0

Xenon

54

0

Radon

86

0

In what way are the Noble Gases unreactive?

• Reason being, the The arrangement of electrons in these gases is very reliable.
• These typically feature Eight outermost electrons in a shell with the exception of helium
• That's why they attain an octet without adding or losing electrons

Instance 1

• Ten electrons make up neon.

• 2 in which these are kept K Shell (since the K shell only has room for 2 electrons)
• 8 of which are kept in L Shell (since there's a cap of 8 electrons in the L Shell)
• Thus, in the highest tier, octet (8) completed
• The fact that they not require any net electron gain or loss Obtain an Octet
• Hence, Neon has no valence. as well as the moniker noble gas, or inert gas

Instance 2

• 2 which these electrons are kept K Shell (Seeing how the K Shell can only accommodate a maximum of 2 electrons)
• 8 held in place by these electrons L Shell (since the L shell only has room for 8)
• Remaining 8 the confinement of electrons M Shell
• Thus, in the highest tier, octet (8) completed
• This entails that not require any electron addition or subtraction in order to form an octet
• Hence, Argon has no valence. and the name for it is noble gas, or inert gas

Note:-

Besides Helium, all other noble gases reach the octet state.

Examples -

In-Text Queston -

Performing Back Exercises with NCERT -

Example 3

• Electron count for Helium: 2
• Everything is included K Shell (since there's a limit of 2 electrons in the K shell)
• Hence the The K shell, the outermost one, is completely occupied.
• Now, they not require any net electron gain or loss

• Hence, Helium has no valence. as well as the moniker a nonreactive substance; a noble gas