Module 5: Valency

📘 Module 5: Valency

(Targeted for Suharshi with beginner-friendly explanations and examples)

🧪 Module 5: Understanding Valency – How Atoms Make Bonds

🎯 Learning Objectives:

• Understand the concept of valency

• Learn how to find valency using electronic configuration

• Memorize valencies of the first 20 elements

• Build a strong base for writing chemical formulas later

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🔹 1. What is Valency?

Valency is the combining capacity of an atom.
In simple words: Valency tells us how many electrons an atom needs to gain, lose, or share to become stable.

🧠 Think of valency as the “handshake number” — how many hands (electrons) an atom offers to bond with other atoms.

Atoms form bonds to complete their outermost shell (called the valence shell). Most elements want to achieve a stable octet (8 electrons) or duet (2 electrons for H and He).

💡 Rule of Thumb:

• Atoms with 1, 2, or 3 electrons in the outer shell → lose them (positive valency)

• Atoms with 5, 6, or 7 electrons → gain electrons to complete 8 (negative valency)

• Atoms with 4 electrons → can gain or lose (valency = 4)

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🔹 2. How to Find Valency Using Electronic Configuration

Step-by-step:

1. Write the electronic configuration.

2. Look at the number of electrons in the outermost shell.

3. Apply these rules:

Valence Electrons	Valency (Lose or Gain)
1	1 (loses 1)
2	2 (loses 2)
3	3 (loses 3)
4	4 (loses or gains 4)
5	3 (gains 3 to make 8)
6	2 (gains 2)
7	1 (gains 1)
8 (noble gases)	0 (already stable)

Examples:

• Hydrogen (H): 1 electron → needs 1 more → valency = 1

• Oxygen (O): 6 electrons → needs 2 → valency = 2

• Sodium (Na): 1 electron → loses 1 → valency = 1

• Chlorine (Cl): 7 electrons → gains 1 → valency = 1

🧠 Fun Fact: Helium has 2 electrons but it’s stable (duet rule). It doesn’t react and has valency 0.

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🔹 3. Valency of First 20 Elements

Atomic No.	Element	E. Configuration	Valence e⁻	Valency
1	Hydrogen	1	1	1
2	Helium	2	2	0
3	Lithium	2,1	1	1
4	Beryllium	2,2	2	2
5	Boron	2,3	3	3
6	Carbon	2,4	4	4
7	Nitrogen	2,5	5	3
8	Oxygen	2,6	6	2
9	Fluorine	2,7	7	1
10	Neon	2,8	8	0
11	Sodium	2,8,1	1	1
12	Magnesium	2,8,2	2	2
13	Aluminium	2,8,3	3	3
14	Silicon	2,8,4	4	4
15	Phosphorus	2,8,5	5	3
16	Sulfur	2,8,6	6	2
17	Chlorine	2,8,7	7	1
18	Argon	2,8,8	8	0
19	Potassium	2,8,8,1	1	1
20	Calcium	2,8,8,2	2	2

🧠 Trick to Remember:

• Group 1 → valency 1 (H, Li, Na, K)

• Group 2 → valency 2 (Be, Mg, Ca)

• Group 17 → valency 1 (F, Cl)

• Noble gases (Group 18) → valency 0

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🎯 Activities for Practice

🧩 Activity 1: Match the Element to its Valency

Match the following:

A. Oxygen → ___
B. Sodium → ___
C. Nitrogen → ___
D. Helium → ___
E. Aluminium → ___

(Options: 1, 2, 3, 0, 3)

🧠 Activity 2: “Valency Detective”

Given:
Atomic Number = 9 → Find element, configuration, valence electrons, and valency.

Atomic Number = 13 → Same task.

📝 Activity 3: Fill in the Table

Element	Atomic No.	E. Configuration	Valence e⁻	Valency
___	7
___	16
___	3

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📌 Summary

• Valency is the combining capacity of an atom.

• It is found using the number of electrons in the outermost shell.

• Elements tend to complete their outer shell (2 or 8 electrons).

• Valency helps us understand how atoms form bonds.

• First 20 elements follow predictable valency rules.