Why is the second IE always higher than the first IE for any element?

📚 Chapter: Classification of Elements and Periodicity in Properties

📘 Detailed Explanation

The second ionization enthalpy (IE₂) is always greater than the first ionization enthalpy (IE₁) because the second electron is removed from a positively charged ion, whereas the first electron is removed from a neutral atom.

First Ionization:
X(g) → X⁺(g) + e⁻

Second Ionization:
X⁺(g) → X²⁺(g) + e⁻

🔹 Why does IE₂ > IE₁?

1. After the first electron is removed, the atom becomes a positively charged ion.
2. The remaining electrons experience a stronger attraction towards the nucleus because the ion has fewer electrons but the same number of protons.
3. The electron-electron repulsion also decreases after removal of the first electron.
4. Therefore, the remaining electron is held more strongly by the nucleus.
5. Consequently, more energy is required to remove the second electron.

IE₂ > IE₁

⚛️ Example: Sodium (Na)

Sodium has atomic number 11 and electronic configuration:

Na = 2, 8, 1

The first electron is removed from the outermost 3s orbital:

Na → Na⁺ + e⁻
2,8,1 → 2,8

After this, Na⁺ has a stable noble-gas configuration of 2,8. The second electron must now be removed from the inner, completely filled shell. It is held very strongly by the nucleus.

Na⁺ → Na²⁺ + e⁻

For Na, the jump from IE₁ to IE₂ is especially large because the second electron must be removed from a stable inner shell.

📊 Comparison

Property	First IE	Second IE
Starting species	Neutral atom	Positive ion
Charge	0	+1
Electron removed	First electron	Second electron
Attraction by nucleus	Relatively lower	Stronger
Energy required	Lower	Higher

✅ Final Answer

The second ionization enthalpy is always higher than the first because after removal of the first electron, the atom becomes a positively charged ion. The remaining electrons are attracted more strongly by the nucleus. Therefore, more energy is required to remove the second electron.

IE₂ > IE₁

20 MCQs with Answers

1. Which is generally greater?

A) IE₁

B) IE₂

C) Both are equal

D) Neither

✅ Answer

B) IE₂

---

2. The second electron is removed from:

A) Neutral atom

B) Negative ion

C) Positive ion

D) Molecule only

✅ Answer

C) Positive ion

---

3. First ionization process is:

A) X → X⁻ + e⁻

B) X → X⁺ + e⁻

C) X⁺ → X²⁺ + e⁻

D) X²⁺ → X³⁺ + e⁻

✅ Answer

B

---

4. Second ionization process is:

A) X → X⁺ + e⁻

B) X⁺ → X²⁺ + e⁻

C) X⁻ → X + e⁻

D) X²⁺ → X + e⁻

✅ Answer

B

---

5. After first ionization, the atom becomes:

A) Neutral

B) Negative

C) Positive

D) Unstable nucleus

✅ Answer

C) Positive

---

6. Why is the second electron held more strongly?

A) More protons are created

B) Remaining electrons experience stronger nuclear attraction

C) Nucleus disappears

D) Electron mass increases

✅ Answer

B

---

7. Which charge is present on the ion before second ionization?

A) 0

B) −1

C) +1

D) +2

✅ Answer

C) +1

---

8. Which has fewer electrons?

A) Neutral atom

B) X⁺

C) Both equal

D) X⁻

✅ Answer

B) X⁺

---

9. Removal of the first electron generally causes electron-electron repulsion to:

A) Increase

B) Decrease

C) Become infinite

D) Remain exactly unchanged

✅ Answer

B) Decrease

---

10. Sodium has electronic configuration:

A) 2,7,2

B) 2,8,1

C) 2,8,2

D) 2,8,8

✅ Answer

B) 2,8,1

---

11. Na⁺ has configuration:

A) 2,8,1

B) 2,8

C) 2,7

D) 2,8,8

✅ Answer

B) 2,8

---

12. For sodium, the second electron is removed from:

A) 3s orbital

B) 2p orbital

C) 1s orbital

D) 3p orbital

✅ Answer

B) 2p orbital

---

13. Which statement is correct?

A) IE₂ < IE₁

B) IE₂ = IE₁ always

C) IE₂ > IE₁

D) IE₂ = 0

✅ Answer

C) IE₂ > IE₁

---

14. The nucleus has:

A) Positive charge

B) Negative charge

C) Zero charge

D) Variable charge only

✅ Answer

A) Positive charge

---

15. Removal of an electron from a cation is:

A) Easier than from neutral atom

B) More difficult than from neutral atom

C) Always impossible

D) Independent of charge

✅ Answer

B

---

16. A very large jump between successive IEs may indicate:

A) Removal of an inner-shell electron after valence electrons are removed

B) Addition of neutrons

C) Formation of nucleus

D) Melting

✅ Answer

A

---

17. Which ion is formed after first ionization?

A) X⁻

B) X⁺

C) X²⁺

D) X²⁻

✅ Answer

B) X⁺

---

18. Ionization enthalpy involves removal of:

A) Proton

B) Neutron

C) Electron

D) Nucleus

✅ Answer

C) Electron

---

19. After one electron is removed, effective attraction on remaining electrons generally:

A) Becomes weaker

B) Becomes stronger

C) Becomes zero

D) Does not exist

✅ Answer

B) Becomes stronger

---

20. The main reason IE₂ is higher than IE₁ is:

A) Second electron is removed from a more positively charged species

B) Second electron has greater mass

C) Nucleus loses a proton

D) Atom becomes larger

✅ Answer

A

Q. Why is the second ionization enthalpy greater than the first ionization enthalpy?

Solution:

After the first electron is removed, the atom becomes a positively charged ion. The remaining electrons are attracted more strongly by the nucleus. Hence, greater energy is required to remove the second electron.

IE₂ > IE₁

Q. Explain why successive ionization enthalpies increase.

Solution:

1. Removal of the first electron converts the atom into a positive ion.
2. The remaining electrons are held more strongly by the nucleus.
3. Electron-electron repulsion also decreases.
4. Therefore, more energy is required for each successive electron.

IE₁ < IE₂ < IE₃ < IE₄ ...

Q. Differentiate between first and second ionization enthalpy.

First Ionization Enthalpy	Second Ionization Enthalpy
X(g) → X⁺(g) + e⁻	X⁺(g) → X²⁺(g) + e⁻
Electron removed from neutral atom	Electron removed from positive ion
Lower energy	Higher energy
IE₁	IE₂ > IE₁

The second electron is more strongly attracted by the nucleus, so its removal requires more energy.

Q. Explain why successive ionization enthalpies of an element increase. Illustrate with sodium.

Solution:

Sodium has electronic configuration 2,8,1. Its first electron is easily removed from the outermost shell:

Na → Na⁺ + e⁻

After this, Na⁺ has the stable configuration 2,8. The second electron must be removed from an inner shell and is therefore held much more strongly.

Na⁺ → Na²⁺ + e⁻

Thus, the second ionization enthalpy is much greater than the first. Similarly, successive ionization enthalpies generally increase.

IE₁ < IE₂ < IE₃ < ...

Q. Why is the second ionization enthalpy always higher than the first? Explain with a suitable example.

Detailed Solution

Ionization enthalpy is the energy required to remove an electron from an isolated gaseous species. The first ionization involves removal of an electron from a neutral atom, whereas the second ionization involves removal of an electron from a positively charged ion.

IE₁: X(g) → X⁺(g) + e⁻

IE₂: X⁺(g) → X²⁺(g) + e⁻

Reasons for IE₂ > IE₁

1. The species after first ionization is positively charged.
2. The number of electrons decreases, while the number of protons remains unchanged.
3. Effective nuclear attraction on the remaining electrons increases.
4. Electron-electron repulsion decreases.
5. The remaining electron is therefore more strongly bound.
6. Consequently, more energy is needed for its removal.

Example: Sodium

Na = 2,8,1
Na⁺ = 2,8

The first electron is removed from the third shell. After its removal, Na⁺ acquires a stable noble-gas configuration. The second electron has to be removed from the inner second shell, which is much more strongly held.

Therefore:

IE₂ > IE₁

and generally,

IE₁ < IE₂ < IE₃ < IE₄ ...

🎯 Quick Revision

IE₁: X → X⁺ + e⁻
IE₂: X⁺ → X²⁺ + e⁻
After IE₁: Positive ion is formed
Nuclear attraction: Increases for remaining electrons
Electron-electron repulsion: Decreases

IE₁ < IE₂ < IE₃ < IE₄ ...