Anand Classes explains that in every atom, electrons are held in place by the strong electrostatic attraction of the positively charged nucleus. This attraction is due to the opposite charges between the negatively charged electrons and the positively charged protons in the nucleus. The outermost or most loosely bound electrons experience a weaker pull compared to the inner electrons because they are farther from the nucleus and shielded by inner shells. To remove such an electron, energy must be supplied to overcome this attraction. The amount of energy needed for this process is called Ionization Enthalpy or Energy (IE) or Ionization Potential (IP). It serves as a quantitative measure in kJ mol⁻¹ of how easily an atom can lose an electron, providing important insight into the atom’s reactivity and chemical behavior.
Table of Contents
📌 Ionization Enthalpy
Electrons in an atom are attracted towards the positively charged nucleus.
To remove an electron, energy must be supplied to overcome this attraction.
This energy is called Ionization Enthalpy.
📗 Definition
Ionization enthalpy is the energy required to remove the most loosely bound electron from an isolated gaseous atom of an element in its ground state.
Ionization Enthalpy is also called: Ionization Potential → because it is the minimum potential difference (in a discharge tube) required to remove the most loosely bound electron and form a gaseous cation.
📏 Units & Conversion of Ionization Enthalpy
| Unit | Symbol | Conversion |
|---|---|---|
| Kilojoule per mole | kJ mol⁻¹ | – |
| Electron volt per atom | eV/atom | 1 eV per atom = 96.49 kJ/mol |
| Kilocalorie per mole | kcal mol⁻¹ | 1 eV per atom = 23.06 kcal/mol |
🔄 Successive Ionization Enthalpies
The atom may not only lose one electron but can lose more than one electrons also. It may be noted that if the gaseous atom is to lose more than one electron, these are removed one after the other. The energies required to remove subsequent electrons from an atom in the gaseous state are known as successive ionization enthalpies.
The energies required to remove subsequent electrons from the atom in the gaseous state, are known as succesive ionization enthalpies. The term first,
second, third. ………. ionisation enthalpy refers to the removal of first, second, third…………..electron respectively.
An atom can lose more than one electron, but they are removed one by one in steps:
1️⃣ First Ionization Enthalpy (IE1)
Energy required to remove the most loosely bound electron from a neutral gaseous atom.
Reaction:
X(g) + IE1 → X+(g) + e−
2️⃣ Second Ionization Enthalpy (IE2)
Energy required to remove the next most loosely bound electron from the singly charged cation.
Reaction:
X+(g) + IE2 → X2+(g) + e−
3️⃣ Third Ionization Enthalpy (IE3)
Energy required to remove the next most loosely bound electron from the doubly charged cation.
Reaction:
X2+(g) + IE3 → X3+(g) + e−
and so on.
Since energy is required to remove electrons from an atom and therefore, ionization enthalpies are always positive.
Thus, the ionization enthalpy gives the ease with which electron can be removed from an atom. Evidently, the smaller the value of ionization
enthalpy, the easier it is to remove the electron from the atom.
Why Successive Ionization Enthalpies Increases (IE1 < IE2 < IE3 <….…) ?
Successive ionization enthalpies increase because of three main reasons:
1️⃣ Decrease in Electron–Electron Repulsion
- When the first electron is removed, the number of electrons decreases, but the nuclear charge remains the same.
- This reduces electron–electron repulsion and allows the nucleus to pull the remaining electrons closer.
2️⃣ Increase in Effective Nuclear Charge (Zeff)
After each electron removal, the positive charge of the ion increases.
- The remaining electrons experience a geater effective nuclear charge, making them more strongly bound to the nucleus.
- Therefore, more energy is required to remove the next electron.
3️⃣ Removal from Inner Shells (Core Electrons)
- After valence electrons are removed, further electrons come from inner shells.
- Inner-shell electrons are much closer to the nucleus and are tightly bound due to strong electrostatic attraction.
- This causes a sudden and large jump in ionization enthalpy values.
📌 In Summary
IE1 < IE2 < IE3 <….…
because:
- Less shielding effect after each removal.
- Increased effective nuclear charge.
- Removal of electrons from more tightly bound shells.
💬 Frequently Asked Questions (FAQs) – Ionization Enthalpy
Q1. Why is ionization enthalpy always positive?
Ans: Because energy must be supplied to overcome the electrostatic attraction between the positively charged nucleus and the negatively charged electron.
Hence
Q2. Why do successive ionization enthalpies always increase?
Ans:
- After each electron is removed, effective nuclear charge increases.
- Remaining electrons are more strongly bound.
- Less shielding effect and sometimes removal from inner shells cause a sudden large jump.
Q3. Why is the second ionization enthalpy always greater than the first?
Ans: In IE2, the electron is removed from a positively charged ion, which has a stronger pull on remaining electrons than a neutral atom.
Q4. What does a large jump in successive ionization enthalpy values indicate?
Ans: It indicates that all valence electrons have been removed and the next electron is being removed from an inner (core) shell.
Q5. How are ionization enthalpy and metallic character related?
Ans:
- Low ionization enthalpy → high metallic character (easy to lose electrons).
- High ionization enthalpy → non-metallic character (hard to lose electrons).
Q6. What are the units of ionization enthalpy?
Ans: kJ mol⁻¹, eV/atom, or kcal mol⁻¹.
Q7. Why is ionization enthalpy of noble gases very high?
Ans: Noble gases have stable completely filled orbitals, making it very difficult to remove an electron.
📌 Key Characteristics of Ionization Enthalpy
- Always positive → Energy is required to overcome nuclear attraction.
- Smaller IE → Easier to remove the electron.
- Larger IE → Electron removal is harder.
📝 Quick Revision Points
- IE measures tendency to lose an electron.
- Always positive.
- Increases with each successive electron removal:
IE1 < IE2 < IE3 <….… - Sharp jump in IE indicates removal of core (inner shell) electrons.
📚 Buy Study Material & Join Our Coaching
For premium study materials specially designed for JEE, NEET, NDA, and CBSE/ICSE Classes, visit our official study material portal:
👉 https://publishers.anandclasses.co.in/
To enroll in our offline or online coaching programs, visit our coaching center website:
👉 https://anandclasses.co.in/
📞 Call us directly at: +91-94631-38669
💬 WhatsApp Us Instantly
Need quick assistance or want to inquire about classes and materials?
📲 Click below to chat instantly on WhatsApp:
👉 Chat on WhatsApp
🎥 Watch Video Lectures
Get access to high-quality video lessons, concept explainers, and revision tips by subscribing to our official YouTube channel:
👉 Neeraj Anand Classes – YouTube Channel
