📘 Answer
Helium (He), with atomic number 2, has the highest first ionization enthalpy among all elements.
🔹 Why does Helium have the highest IE?
- Helium has a very small atomic size.
- Its electrons are very close to the nucleus.
- It has a high effective nuclear attraction on its electrons.
- Its electronic configuration is 1s², which is a stable and completely filled shell.
- Therefore, a large amount of energy is required to remove an electron.
📈 Periodic Trend
Ionization enthalpy generally:
Helium is located at the top-right corner of the periodic table, where the first ionization enthalpy is maximum.
⚛️ Comparison with Other Noble Gases
| Element | Electronic Configuration | Relative IE |
|---|---|---|
| He | 1s² | Highest |
| Ne | 2s²2p⁶ | Very High |
| Ar | 3s²3p⁶ | High |
Although noble gases have high ionization enthalpies because of their stable closed-shell configurations, helium has the highest due to its very small size and strong nuclear attraction.
✅ Final Answer
Helium (He) has the highest first ionization enthalpy in the periodic table because it has a very small atomic size, high effective nuclear attraction, and a stable 1s² electronic configuration.
20 MCQs with Answers
1. Which element has the highest first ionization enthalpy?
✅ Answer
B) He
2. The atomic number of helium is:
✅ Answer
B) 2
3. Electronic configuration of He is:
✅ Answer
B) 1s²
4. Helium has high IE mainly because of its:
✅ Answer
B) Small size
5. Ionization enthalpy generally increases across a period from:
✅ Answer
B) Left to right
6. Ionization enthalpy generally decreases:
✅ Answer
B) Down a group
7. Helium belongs to:
✅ Answer
D) Group 18
8. Helium is a:
✅ Answer
C) Noble gas
9. Which factor strongly contributes to high IE of He?
✅ Answer
B
10. The valence shell of helium contains:
✅ Answer
B) 2 electrons
11. Which has higher first IE?
✅ Answer
B) He
12. Noble gases generally have:
✅ Answer
B) High IE
13. The nucleus attracts electrons because the nucleus is:
✅ Answer
B) Positively charged
14. A smaller atomic radius generally results in:
✅ Answer
B) Higher IE
15. Which element is at the top-right of the periodic table?
✅ Answer
B) He
16. Stable configuration of He is:
✅ Answer
B
17. Which has the smallest atomic size among the noble gases?
✅ Answer
A) He
18. High ionization enthalpy means an electron is:
✅ Answer
B) Difficult to remove
19. Which statement is correct?
✅ Answer
B
20. The highest first ionization enthalpy in the periodic table belongs to:
✅ Answer
B) Helium
Q. Which element has the highest first ionization enthalpy? Give one reason.
Solution: Helium (He) has the highest first ionization enthalpy because it has a very small atomic size and its electrons are strongly attracted by the nucleus.
Q. Why does helium have the highest first ionization enthalpy?
Solution:
- Helium has a very small atomic radius.
- Its electrons are very close to the nucleus.
- Its stable configuration is 1s².
- Therefore, its electron is held very strongly and requires maximum energy for removal.
Q. Explain the periodic trend of ionization enthalpy and identify the element having the highest first IE.
Solution:
- Ionization enthalpy generally increases from left to right across a period.
- It generally decreases from top to bottom in a group.
- The highest value occurs at the top-right of the periodic table.
- Helium (He) has the highest first ionization enthalpy.
Q. Explain why helium has the highest ionization enthalpy among all elements.
Solution:
- Helium has atomic number 2 and electronic configuration 1s².
- It has only one occupied electron shell.
- The atomic size of helium is extremely small.
- Its electrons experience strong attraction from the nucleus.
- The 1s orbital is completely filled and highly stable.
- Therefore, a very large amount of energy is required to remove an electron.
Q. What is ionization enthalpy? Explain its periodic trend and state which element has the highest first ionization enthalpy.
Detailed Solution
Ionization enthalpy is the minimum energy required to remove the most loosely bound electron from an isolated gaseous atom in its ground state.
Trend Across a Period
From left to right, effective nuclear charge generally increases and atomic size decreases. Therefore, electrons are held more strongly and ionization enthalpy generally increases.
Trend Down a Group
Down a group, new shells are added. Atomic size and shielding effect increase, so the outer electron is easier to remove. Hence, ionization enthalpy generally decreases.
Highest Ionization Enthalpy
Helium has the highest first ionization enthalpy because of its very small size, high effective nuclear attraction, and stable completely filled 1s² configuration.
Highest First Ionization Enthalpy = Helium (He)
🎯 Quick Revision
Atomic Number: 2
Configuration: 1s²
Group: 18
Period: 1
Across Period: IE generally ↑
Down Group: IE generally ↓
