Electronic configuration and valency: Class 9 practice
Electrons fill shells K, L, M, N with at most 2, 8, 8 (for the first 20 elements) electrons. Read the method, follow the three worked examples, then try the six questions.
What you should know first
- Atomic number
The idea behind electronic configuration and valency
Electrons fill shells K, L, M, N with at most 2, 8, 8 (for the first 20 elements) electrons. Valency is the number of electrons lost or gained to reach a full outer shell: outer electrons if ≤ 4, otherwise 8 minus outer electrons.
Step-by-step method
- Fill K (2), L (8), M (8), N.
- Count outer-shell electrons.
- Valency = outer if ≤ 4, else 8 − outer.
Worked example 1 (Basic)
Write the electronic configuration and valency of the element with atomic number 8.
- Configuration: 2, 6
- Outer electrons: 6
- Valency: 2
- Answer: 2, 6; valency 2
Worked example 2 (Standard)
Write the electronic configuration and valency of the element with atomic number 17.
- Configuration: 2, 8, 7
- Outer electrons: 7
- Valency: 1
- Answer: 2, 8, 7; valency 1
Worked example 3 (Challenge)
Write the electronic configuration and valency of the element with atomic number 19.
- Configuration: 2, 8, 8, 1
- Outer electrons: 1
- Valency: 1
- Answer: 2, 8, 8, 1; valency 1
Common mistakes and misconceptions
- Putting 18 in M for Class 9 elements
- Confusing valency with outer electrons for non-metals
Practice questions
- (Basic) Write the electronic configuration and valency of the element with atomic number 9.
- (Basic) Write the electronic configuration and valency of the element with atomic number 3.
- (Standard) Write the electronic configuration and valency of the element with atomic number 20.
- (Standard) Write the electronic configuration and valency of the element with atomic number 13.
- (Challenge) Write the electronic configuration and valency of the element with atomic number 11.
- (Challenge) Write the electronic configuration and valency of the element with atomic number 18.
Answer key with full working
- Q1: Configuration: 2, 7 → Outer electrons: 7 → Valency: 1 → Answer: 2, 7; valency 1
- Q2: Configuration: 2, 1 → Outer electrons: 1 → Valency: 1 → Answer: 2, 1; valency 1
- Q3: Configuration: 2, 8, 8, 2 → Outer electrons: 2 → Valency: 2 → Answer: 2, 8, 8, 2; valency 2
- Q4: Configuration: 2, 8, 3 → Outer electrons: 3 → Valency: 3 → Answer: 2, 8, 3; valency 3
- Q5: Configuration: 2, 8, 1 → Outer electrons: 1 → Valency: 1 → Answer: 2, 8, 1; valency 1
- Q6: Configuration: 2, 8, 8 → Outer electrons: 8 → Valency: 0 → Answer: 2, 8, 8; valency 0
Syllabus note
This skill is listed under "Structure of the Atom" for Class 9 in the NCERT/CBSE books. ICSE, IGCSE, IB and state boards may teach it in a different chapter or year.
Answers on this page are generated and automatically re-checked by a second, independent calculation. They have not been reviewed by a teacher — if you spot a problem, tell us on WhatsApp.
Related practice and notes
Frequently asked questions
Which chapter is electronic configuration and valency in?
"Structure of the Atom", Class 9 Chemistry (NCERT/CBSE). Other boards may place it differently.
How were the answers checked?
Answers on this page are generated and automatically re-checked by a second, independent calculation. They have not been reviewed by a teacher — if you spot a problem, tell us on WhatsApp.