Anand Classes explain how To find the position of an element in the periodic table, we can use its electronic configuration. This helps us easily determine the period, group, and block to which the element belongs. In this post, we’ll go through simple solved examples to understand how to apply these rules step by step. This is very helpful for students preparing for JEE, NEET, and CBSE Class 11 exams.
Table of Contents
🧪 Solved Examples – Prediction of Element Position in the Periodic Table
Q: Predict the position of an element in the periodic table having the electronic configuration of (n–1)d1ns2 for n = 4. [NCERT]
Solution: Given: n = 4
Electronic configuration = 3d1 4s2
✅ The last electron enters the 3d orbital, so it’s a d-block element.
👉 Group number = electrons in (n−1)d + electrons in ns
Group number = 1 (from 3d) + 2 (from 4s) = 3
🧾 Final Answer:
- Block: d-block
- Group: 3
- Period: 4
Q: (a) Elements A, B, C, and D have atomic numbers 12, 19, 29, and 36 respectively. Identify their groups based on electronic configuration. (b) Predict their blocks, periods, and groups. (c) Which of these are representative elements? [NCERT]
Solution: ✅ (a) Electronic Configuration and Group No. :
| Element | Atomic Number | Electronic Configuration | Group |
|---|---|---|---|
| A | 12 | 1s² 2s² 2p⁶ 3s² | 2 |
| B | 19 | 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ | 1 |
| C | 29 | 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s¹ | 11 |
| D | 36 | 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ | 18 |
✅ (b) Prediction of Block, Period, and Group:
- A (Z = 12):
- Last electron → 3s orbital ⇒ s-block
- Period = 3rd
- Group = Valence electrons = 2
- B (Z = 19):
- Last electron → 4s orbital ⇒ s-block
- Period = 4th
- Group = Valence electrons = 1
- C (Z = 29):
- Last electron → 3d orbital ⇒ d-block
- Period = 4th
- Group = (3d¹⁰ + 4s¹) = 11
- D (Z = 36):
- Last electron → 4p orbital ⇒ p-block
- Period = 4th
- Group = 10 + valence electrons = 10 + 8 = 18
✅ (c) Representative Elements:
✔️ A (Z = 12) and B (Z = 19) are representative elements (s- and p-block main group elements).
Q: Identify the elements based on their electronic configurations. Also, answer the questions given below: [NCERT]
| Configuration | Element |
|---|---|
| (i) 1s² 2s² 2p⁶ 3s¹ | Sodium (Na) |
| (ii) 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹ | Scandium (Sc) |
| (iii) 1s² 2s² 2p³ | Nitrogen (N) |
| (iv) 1s² 2s² 2p⁶ 3s² | Calcium (Ca) |
| (v) 1s² 2s² 2p⁶ 3s² 3p⁵ | Chlorine (Cl) |
| (vi) 1s² 2s² 2p⁶ 3s² 3p³ | Phosphorus (P) |
| (vii) 1s² 2s² 2p⁶ | Neon (Ne) |
| (viii) 1s² 2s² 2p⁶ 3s² 3p⁴ | Sulphur (S) |
✅ Answers:
- Alkaline earth metal: Calcium (iv)
- Lowest chemical reactivity: Neon (vii)
- Group 15 elements: Nitrogen (iii), Phosphorus (vi)
- Transition element: Scandium (ii)
- Halogen: Chlorine (v)
- p-block elements: Nitrogen, Chlorine, Phosphorus, Neon, Sulphur
- Second period elements: Nitrogen (iii), Neon (vii)
Q: The electronic configurations of the elements are as follows:
| Element | Electronic Configuration |
|---|---|
| A | 1s² 2s² 2p¹ |
| B | 1s² 2s² 2p⁶ 3s² 3p¹ |
| C | 1s² 2s² 2p⁶ 3s² 3p³ |
| D | 1s² 2s² 2p⁶ 3s² 3p⁵ |
| E | 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² |
Which of these elements belong to the same group in the periodic table? [NCERT]
Solution: Elements with the same number of valence electrons belong to the same group.
✔️ Element A and B both have 3 valence electrons → belong to Group 13.
Q. The elements Z = 107, 108 and Z = 109 have been made recently. Indicate the group in which you will place the above elements. [NCERT]
Solution: In recent times, scientists have successfully created new superheavy elements with atomic numbers 107, 108, and 109. Let’s understand how to predict their position in the periodic table using their electronic configurations.
🧪 Electronic Configurations:
- Z = 107 → [Rn] 5f¹⁴ 6d⁵ 7s²
- Z = 108 → [Rn] 5f¹⁴ 6d⁶ 7s²
- Z = 109 → [Rn] 5f¹⁴ 6d⁷ 7s²
✅ In all three cases, the last electrons enter the 6d subshell, which means these elements belong to the d-block (transition elements).
📌 Group Prediction:
To find the group number for d-block elements, we use the rule:
Group number = Number of electrons in (n–1)d subshell + Number of electrons in the valence (ns) shell
Let’s apply the formula:
| Atomic Number | Configuration | d-electrons | s-electrons | Group Number |
|---|---|---|---|---|
| Z = 107 | 6d⁵ 7s² | 5 | 2 | 7 |
| Z = 108 | 6d⁶ 7s² | 6 | 2 | 8 |
| Z = 109 | 6d⁷ 7s² | 7 | 2 | 9 |
✅ Final Answer:
- Element 107 → Group 7
- Element 108 → Group 8
- Element 109 → Group 9
- All are part of the d-block in the periodic table.
🔖 These elements are classified as superheavy transition metals, and their chemical properties are still under active research. However, based on periodic trends and electronic configurations, their group placement follows standard rules.
📝 Conclusion:
By analyzing electronic configurations, we can accurately predict an element’s:
- Block (s, p, d, f)
- Period (from the valence shell)
- Group (using rules for each block)
This knowledge is essential for understanding trends in the periodic table and solving problems in competitive exams.
🔖 Related Topics:
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