Compare the size of a neutral atom with its Cation and Anion.

📚 Chapter: Classification of Elements and Periodicity in Properties

📘 Detailed Explanation

🔵 Basic Comparison

The size of an atom changes when it gains or loses electrons. Therefore, the radius of a neutral atom is different from the radius of its cation or anion.

Cation < Neutral Atom < Anion

Positive ion  <  Neutral atom  <  Negative ion

🔴 Cation – Smaller than Neutral Atom

A cation is formed when a neutral atom loses one or more electrons.

After losing electrons, the number of electrons decreases while the nuclear charge remains the same. In many cases, the outermost shell is completely lost. Hence, the remaining electrons are attracted more strongly towards the nucleus.

Neutral Atom → Loss of e⁻ → Cation → Size Decreases

Example:

Na → Na⁺ + e⁻

The sodium atom is larger than the sodium ion:

Na > Na⁺

🟢 Anion – Larger than Neutral Atom

An anion is formed when a neutral atom gains one or more electrons.

The nuclear charge remains unchanged, but the number of electrons increases. This increases electron-electron repulsion and reduces the effective attraction experienced by each electron. Therefore, the electron cloud expands.

Neutral Atom → Gain of e⁻ → Anion → Size Increases

Example:

Cl + e⁻ → Cl⁻

The chloride ion is larger than the chlorine atom:

Cl < Cl⁻

📊 Comparison Table

Species	Electron Change	Effect on Size	Reason
Cation (+)	Loss of electrons	Smaller	Greater effective attraction and often loss of outer shell
Neutral Atom	No gain/loss	Reference size	Normal balance of nuclear attraction and electron repulsion
Anion (−)	Gain of electrons	Larger	Greater electron-electron repulsion

🔬 Example with Isoelectronic Species

Consider Na⁺, Ne and F⁻. All three species have 10 electrons, but their nuclear charges are different.

Na⁺  ,  Ne  ,  F⁻

Na⁺ has the greatest nuclear charge among these three and therefore has the smallest radius, while F⁻ has the lowest nuclear charge and the largest radius.

Na⁺ < Ne < F⁻

✅ Final Answer

A cation is smaller than its neutral atom because it loses electrons, whereas an anion is larger because it gains electrons and experiences increased electron-electron repulsion.

Cation < Neutral Atom < Anion

📝 20 MCQs with Answers

1. Which is generally the smallest?

A) Anion

B) Neutral atom

C) Cation

D) All are equal

✅ Answer

C) Cation

---

2. A cation is formed by:

A) Gain of electrons

B) Loss of electrons

C) Gain of neutrons

D) Gain of protons only

✅ Answer

B) Loss of electrons

---

3. An anion is generally ______ than its neutral atom.

A) Smaller

B) Larger

C) Equal

D) Massless

✅ Answer

B) Larger

---

4. A cation is generally ______ than its neutral atom.

A) Larger

B) Smaller

C) Equal

D) Unstable only

✅ Answer

B) Smaller

---

5. Which sequence is generally correct?

A) Anion < Atom < Cation

B) Cation < Atom < Anion

C) Atom < Cation < Anion

D) Cation = Atom = Anion

✅ Answer

B) Cation < Atom < Anion

---

6. What happens to the number of electrons when a cation forms?

A) Increases

B) Decreases

C) Remains unchanged

D) Doubles

✅ Answer

B) Decreases

---

7. What happens to the number of electrons when an anion forms?

A) Decreases

B) Increases

C) Becomes zero

D) Remains unchanged

✅ Answer

B) Increases

---

8. Which ion is smaller than Na?

A) Na⁺

B) Na⁻

C) Both are larger

D) None

✅ Answer

A) Na⁺

---

9. Which ion is larger than Cl?

A) Cl⁺

B) Cl⁻

C) Both are smaller

D) Neither

✅ Answer

B) Cl⁻

---

10. Formation of an anion increases:

A) Electron-electron repulsion

B) Proton number

C) Nuclear charge

D) Atomic number

✅ Answer

A) Electron-electron repulsion

---

11. During ion formation, the number of protons generally:

A) Changes

B) Remains unchanged

C) Becomes zero

D) Doubles

✅ Answer

B) Remains unchanged

---

12. Which has greater electron-electron repulsion?

A) Anion

B) Cation

C) Proton

D) Nucleus

✅ Answer

A) Anion

---

13. The radius of Na⁺ is smaller than Na because:

A) Na⁺ gains electrons

B) Na⁺ loses an electron and has stronger effective attraction

C) Na⁺ gains a shell

D) Nuclear charge disappears

✅ Answer

B)

---

14. The radius of Cl⁻ is larger than Cl because:

A) It loses electrons

B) It gains an electron

C) It loses protons

D) It loses a shell

✅ Answer

B) It gains an electron

---

15. Which species has a positive charge?

A) Anion

B) Cation

C) Neutral atom

D) Isotope

✅ Answer

B) Cation

---

16. Which species has a negative charge?

A) Cation

B) Anion

C) Neutral atom

D) Nucleus

✅ Answer

B) Anion

---

17. Which has the largest radius in the simple comparison?

A) Cation

B) Neutral atom

C) Anion

D) Nucleus

✅ Answer

C) Anion

---

18. Correct order for size is:

A) Cl⁻ < Cl < Cl⁺

B) Cl⁺ < Cl < Cl⁻

C) Cl < Cl⁻ < Cl⁺

D) All equal

✅ Answer

B) Cl⁺ < Cl < Cl⁻

---

19. Which statement is correct?

A) Cations are generally larger than atoms

B) Anions are generally smaller than atoms

C) Cations are generally smaller and anions generally larger than their parent atoms

D) Ion formation never affects size

✅ Answer

C)

---

20. The correct general relationship is:

A) Cation > Atom > Anion

B) Anion > Atom > Cation

C) Atom > Anion > Cation

D) Cation = Atom = Anion

✅ Answer

B) Anion > Atom > Cation

Q. Compare the size of a neutral atom with its cation and anion.

Solution:

• A cation is smaller than its neutral atom because it loses electrons.
• An anion is larger than its neutral atom because it gains electrons, increasing electron-electron repulsion.

Cation < Neutral Atom < Anion

Q. Explain why cations are smaller and anions are larger than their parent atoms.

Solution:

1. Cation: Loss of electrons reduces electron-electron repulsion and may remove the outermost shell, making the ion smaller.
2. Anion: Gain of electrons increases electron-electron repulsion, causing expansion of the electron cloud.
3. The number of protons does not change during ordinary ion formation.

Therefore: Cation < Neutral Atom < Anion

Q. Differentiate between the size of a neutral atom, cation and anion.

Species	Electron Change	Relative Size	Main Reason
Cation	Loses e⁻	Smaller	Greater effective attraction; possible loss of outer shell
Neutral Atom	No change	Normal	Reference size
Anion	Gains e⁻	Larger	Increased electron-electron repulsion

Size order: Cation < Neutral Atom < Anion

Q. Explain the change in atomic size when an atom forms a cation or an anion.

Solution:

Formation of Cation

When an atom loses one or more electrons, a positive ion called a cation is formed. The number of protons remains unchanged, but the number of electrons decreases. The remaining electrons experience stronger attraction from the nucleus. If the complete outer shell is lost, the decrease in size is even more significant.

Formation of Anion

When an atom gains one or more electrons, a negative ion called an anion is formed. The nuclear charge remains unchanged, but electron-electron repulsion increases. Consequently, the electron cloud expands and the ionic radius becomes larger.

Cation < Neutral Atom < Anion

Q. Compare the size of a neutral atom, its cation and anion. Explain the reasons with suitable examples.

Detailed Solution

The size of an atom or ion is expressed in terms of its atomic or ionic radius. Formation of an ion involves the loss or gain of electrons, while the number of protons remains unchanged. This produces a significant change in size.

1. Cation

A cation is formed by the loss of electrons. Since the nuclear charge remains the same but fewer electrons are present, the attraction between the nucleus and the remaining electrons becomes stronger. In some cases, the entire outermost shell is removed.

Na → Na⁺ + e⁻
Na⁺ is smaller than Na.

2. Neutral Atom

A neutral atom has an equal number of protons and electrons. Its size lies between the sizes of its corresponding cation and anion in the simple comparison.

3. Anion

An anion is formed by gaining electrons. Since the nuclear charge remains unchanged but the number of electrons increases, electron-electron repulsion increases. The electron cloud expands and the ionic radius increases.

Cl + e⁻ → Cl⁻
Cl⁻ is larger than Cl.

📊 Overall Comparison

Species	Electron Change	Size
Cation (+)	Loss	Smallest
Neutral Atom	No change	Intermediate
Anion (−)	Gain	Largest

🎯 Final Answer:

A cation is generally smaller than its neutral atom because it loses electrons and experiences stronger effective nuclear attraction. An anion is generally larger because it gains electrons, increasing electron-electron repulsion and expanding the electron cloud.

Cation < Neutral Atom < Anion

🎯 Quick Revision

Lose e⁻ → Cation → Size ↓
Neutral Atom → Normal Size
Gain e⁻ → Anion → Size ↑

Cation < Neutral Atom < Anion

Why does the atomic size decrease from left to right across a period?

📚 Chapter: Classification of Elements and Periodicity in Properties

📘 Detailed Explanation

🔵 Trend Across a Period

The atomic size generally decreases from left to right across a period in the periodic table.

➡️ Left to Right → Atomic Radius Decreases ⬇️

The main reason is that the number of protons in the nucleus increases while the newly added electrons enter the same principal energy level.

🟣 Main Reason: Increase in Effective Nuclear Charge

As we move from left to right, the atomic number increases. Therefore, the number of protons increases.

Na → Mg → Al → Si → Cl

At the same time, the additional electrons are added to the same shell. The shielding effect does not increase enough to cancel the increasing positive charge of the nucleus.

Protons ↑ → Effective Nuclear Charge ↑ → Attraction ↑ → Atomic Size ↓

🟢 What Happens to the Electrons?

Quantity	Left → Right
Atomic number	Increases
Number of protons	Increases
Electrons in same shell	Increase
Effective nuclear charge	Increases
Attraction between nucleus and electrons	Increases
Atomic radius	Decreases

⚡ Example: Period 3

Consider the third period:

Na → Mg → Al → Si → P → S → Cl → Ar

The nuclear charge continuously increases from Na to Ar, while electrons are added to the same third shell. Hence, the electron cloud is pulled closer to the nucleus and the atomic radius generally decreases.

Na > Mg > Al > Si > P > S > Cl

✅ Final Answer

Atomic size decreases from left to right across a period because the nuclear charge increases while electrons are added to the same principal energy level. The increased effective nuclear charge attracts the electrons more strongly towards the nucleus, thereby decreasing the atomic radius.

Across a period → Effective nuclear charge ↑ → Atomic size ↓

📝 20 MCQs with Answers

1. Atomic size generally ______ from left to right across a period.

A) Increases

B) Decreases

C) Remains constant

D) First increases then remains constant

✅ Answer

B) Decreases

---

2. The main reason for the decrease in atomic size across a period is:

A) Decrease in nuclear charge

B) Increase in effective nuclear charge

C) Addition of new shells

D) Decrease in electrons

✅ Answer

B) Increase in effective nuclear charge

---

3. From left to right across a period, the number of protons:

A) Decreases

B) Increases

C) Remains constant

D) Becomes zero

✅ Answer

B) Increases

---

4. The added electrons across a period generally enter:

A) A new principal shell each time

B) The same principal energy level

C) The nucleus

D) The previous shell only

✅ Answer

B) The same principal energy level

---

5. Effective nuclear charge across a period generally:

A) Decreases

B) Increases

C) Remains zero

D) Becomes unpredictable

✅ Answer

B) Increases

---

6. Greater effective nuclear charge causes stronger:

A) Nuclear-electron attraction

B) Electron-electron repulsion only

C) Neutron attraction

D) Nuclear fission

✅ Answer

A) Nuclear-electron attraction

---

7. Which element generally has a smaller atomic radius?

A) Na

B) Cl

C) Mg

D) Al

✅ Answer

B) Cl

---

8. Atomic size is usually measured using:

A) Atomic radius

B) Atomic mass only

C) Number of neutrons

D) Melting point

✅ Answer

A) Atomic radius

---

9. Which period shows the sequence Na → Ar?

A) Period 1

B) Period 2

C) Period 3

D) Period 4

✅ Answer

C) Period 3

---

10. From Na to Cl, atomic radius generally:

A) Increases

B) Decreases

C) Remains constant

D) Doubles

✅ Answer

B) Decreases

---

11. Which factor does NOT increase significantly across a period?

A) Nuclear charge

B) Number of protons

C) Number of principal shells

D) Atomic number

✅ Answer

C) Number of principal shells

---

12. Across a period, shielding effect due to inner shells:

A) Changes only slightly

B) Becomes zero

C) Decreases to zero

D) Completely cancels nuclear charge

✅ Answer

A) Changes only slightly

---

13. Which statement is correct?

A) More nuclear charge generally means a larger atom across a period

B) More effective nuclear charge generally means a smaller atom across a period

C) Atomic size is independent of nuclear charge

D) Atomic size always increases across a period

✅ Answer

B)

---

14. The attraction between nucleus and valence electrons across a period:

A) Generally increases

B) Generally decreases

C) Remains exactly constant

D) Disappears

✅ Answer

A) Generally increases

---

15. Which has a larger atomic size?

A) Na

B) Cl

C) Ar

D) S

✅ Answer

A) Na

---

16. What happens to the electron cloud across a period?

A) It is generally pulled closer to the nucleus

B) It moves infinitely far away

C) It disappears

D) It gains a completely new shell

✅ Answer

A)

---

17. Which quantity increases from Na to Cl?

A) Atomic radius

B) Effective nuclear charge

C) Number of principal shells

D) Distance of the outer shell from nucleus

✅ Answer

B) Effective nuclear charge

---

18. The general periodic trend of atomic radius across a period is:

A) Left → Right: increases

B) Left → Right: decreases

C) Left → Right: remains constant

D) No trend

✅ Answer

B)

---

19. Which is responsible for pulling electrons closer to the nucleus?

A) Increased effective nuclear charge

B) Decreased proton number

C) Addition of new shells

D) Decreased nuclear attraction

✅ Answer

A)

---

20. The correct relationship is:

A) Effective nuclear charge ↑ → Atomic radius ↑

B) Effective nuclear charge ↑ → Atomic radius ↓

C) Effective nuclear charge ↓ → Atomic radius ↓

D) No relationship

✅ Answer

B)

Q. Why does atomic size decrease from left to right across a period?

Solution: Atomic size decreases because the nuclear charge increases while electrons are added to the same shell. The increased effective nuclear charge attracts the electrons more strongly towards the nucleus.

Nuclear charge ↑ → Attraction ↑ → Atomic size ↓

Q. Explain the decrease in atomic radius across a period.

Solution:

1. The number of protons increases from left to right.
2. Electrons are added to the same principal energy level.
3. Effective nuclear charge increases, pulling the electrons closer to the nucleus.

Hence, atomic radius decreases from left to right.

Q. Explain the periodic trend of atomic size across a period.

Property	Left → Right
Atomic number	Increases
Number of protons	Increases
Principal energy levels	Same
Effective nuclear charge	Increases
Attraction on electrons	Increases
Atomic radius	Decreases

Therefore: Atomic size decreases across a period.

Q. Discuss the factors responsible for the decrease in atomic size from left to right across a period.

Solution:

• Increasing atomic number: The number of protons increases successively.
• Same principal shell: The added electrons enter the same main energy level.
• Effective nuclear charge increases: The increased nuclear charge is not completely cancelled by shielding.
• Stronger attraction: The nucleus attracts the electrons more strongly.
• Atomic radius decreases: The electron cloud is pulled closer to the nucleus.

General Trend:

Left → Right across a period:
Effective Nuclear Charge ↑ → Atomic Radius ↓

Q. Explain in detail why atomic size decreases from left to right across a period. Give a suitable example.

Detailed Solution:

Atomic size refers to the distance from the nucleus to the outermost occupied electron shell. Across a period, atomic size generally decreases from left to right.

The main reason is the progressive increase in effective nuclear charge. As we move from left to right, the atomic number increases, so the number of protons in the nucleus increases.

At the same time, the newly added electrons enter the same principal energy level. Therefore, the shielding effect does not increase enough to offset the increasing positive charge of the nucleus.

Factor	Trend Left → Right
Atomic number	↑
Protons	↑
New principal shell	Not added
Effective nuclear charge	↑
Nuclear attraction	↑
Atomic radius	↓

Example: Third Period

Na → Mg → Al → Si → P → S → Cl

From Na to Cl, the nuclear charge increases continuously while the electrons are added to the same third shell. Therefore, the effective nuclear attraction increases and the atomic radius generally decreases.

Across a period → Nuclear charge ↑ → Effective nuclear charge ↑ → Atomic radius ↓

🎯 Final Answer:

The atomic size decreases from left to right across a period because the number of protons increases while the added electrons enter the same principal energy level. Thus, effective nuclear charge increases, causing stronger attraction between the nucleus and the electrons. Consequently, the electron cloud is pulled closer to the nucleus and the atomic radius decreases.

🎯 Quick Revision

Left → Right Across a Period
Atomic Number ↑
Protons ↑
Same Principal Shell
Effective Nuclear Charge ↑
Nuclear Attraction ↑
Atomic Radius ↓

Define Isoelectronic species with two examples.

📚 Chapter: Classification of Elements and Periodicity in Properties

📘 Detailed Explanation

🔵 Trend Down a Group

The ionic radius generally increases down a group in the periodic table.

⬇️ Down the Group → Ionic Radius Increases ⬆️

This happens because a new electron shell is added as we move from one period to the next. The outermost electrons are therefore located farther from the nucleus.

🟣 Main Reasons

1. Increase in number of shells: Each successive element down a group has an additional principal energy level.
2. Increase in shielding effect: Inner electrons shield the valence electrons from the attraction of the nucleus.
3. Greater distance from nucleus: The outermost electron shell lies farther away from the nucleus.

More shells + More shielding → Larger ionic radius

🟢 Example: Group 1 Cations

Consider the alkali metal ions:

Li⁺ < Na⁺ < K⁺ < Rb⁺ < Cs⁺

Ionic radius increases from Li⁺ → Cs⁺.

⚡ Important Point: Cations and Anions

Type	Effect
Cation (+)	Smaller than its parent atom
Anion (−)	Larger than its parent atom

However, within a particular group, both cationic and anionic radii generally increase as we move downward because additional electron shells are added.

✅ Final Answer

The ionic radius increases down a group because the number of electron shells increases, resulting in greater shielding and a greater distance between the nucleus and the outermost electron shell.

Down the group ↓ → Ionic radius ↑

📝 20 MCQs with Answers

1. What happens to ionic radius down a group?

A) Decreases

B) Increases

C) Remains constant

D) Becomes zero

✅ Answer

B) Increases

---

2. The main reason for increasing ionic radius down a group is:

A) Decrease in shells

B) Addition of electron shells

C) Decrease in nuclear charge

D) Loss of protons

✅ Answer

B) Addition of electron shells

---

3. Shielding effect down a group generally:

A) Decreases

B) Increases

C) Becomes zero

D) Remains exactly constant

✅ Answer

B) Increases

---

4. Which has the larger ionic radius?

A) Li⁺

B) Na⁺

C) Both are equal

D) Cannot be compared

✅ Answer

B) Na⁺

---

5. Correct order of Group 1 ionic radii is:

A) Li⁺ > Na⁺ > K⁺

B) Li⁺ < Na⁺ < K⁺

C) K⁺ < Na⁺ < Li⁺

D) Na⁺ < Li⁺ < K⁺

✅ Answer

B) Li⁺ < Na⁺ < K⁺

---

6. Down a group, the number of occupied shells:

A) Decreases

B) Increases

C) Remains constant

D) Becomes zero

✅ Answer

B) Increases

---

7. Which factor increases the distance of the outermost electrons from the nucleus?

A) Addition of electron shells

B) Removal of shells

C) Decrease in atomic number

D) Nuclear contraction only

✅ Answer

A) Addition of electron shells

---

8. Which statement is correct?

A) Ionic radius always decreases down every group

B) Ionic radius generally increases down a group

C) Ionic radius is independent of shells

D) Ionic radius is always constant

✅ Answer

B) Ionic radius generally increases down a group

---

9. A cation is generally ______ than its parent atom.

A) Larger

B) Smaller

C) Equal

D) Heavier only

✅ Answer

B) Smaller

---

10. An anion is generally ______ than its parent atom.

A) Smaller

B) Larger

C) Equal

D) Without electrons

✅ Answer

B) Larger

---

11. Which ion is expected to have the largest radius?

A) Li⁺

B) Na⁺

C) K⁺

D) Rb⁺

✅ Answer

D) Rb⁺

---

12. What is the effect of inner electrons on outer electrons?

A) Shielding

B) Bonding

C) Ionisation

D) Fusion

✅ Answer

A) Shielding

---

13. Which quantity generally increases down a group?

A) Ionic radius

B) Nuclear attraction on outermost shell

C) Electronegativity

D) Ionisation energy

✅ Answer

A) Ionic radius

---

14. The outermost electron shell becomes:

A) Closer to nucleus down a group

B) Farther from nucleus down a group

C) Absent

D) Identical for all elements

✅ Answer

B) Farther from nucleus down a group

---

15. Which pair represents a correct trend?

A) Down group → radius decreases

B) Down group → radius increases

C) Down group → shells decrease

D) Down group → shielding decreases

✅ Answer

B) Down group → radius increases

---

16. Ionic radius is a measure of:

A) Size of an ion

B) Mass of an ion

C) Number of neutrons only

D) Melting point

✅ Answer

A) Size of an ion

---

17. Which has a greater ionic radius?

A) K⁺

B) Li⁺

C) Both equal

D) H⁺

✅ Answer

A) K⁺

---

18. The shielding effect is caused mainly by:

A) Inner-shell electrons

B) Protons only

C) Neutrons only

D) Nucleus only

✅ Answer

A) Inner-shell electrons

---

19. Which sequence shows increasing ionic radius?

A) Li⁺ < Na⁺ < K⁺

B) K⁺ < Na⁺ < Li⁺

C) Na⁺ < Li⁺ < K⁺

D) Li⁺ > K⁺ > Na⁺

✅ Answer

A) Li⁺ < Na⁺ < K⁺

---

20. The best explanation for increasing ionic radius down a group is:

A) More electron shells and greater shielding

B) Fewer electron shells

C) Fewer protons

D) Complete removal of electrons

✅ Answer

A) More electron shells and greater shielding

Q. State the trend of ionic radii down a group.

Solution: Ionic radius generally increases down a group because a new electron shell is added at each successive period. The increased shielding effect also places the outermost electrons farther from the nucleus.

Down the group ↓ → Ionic radius ↑

Q. Why does ionic radius increase down a group?

Solution:

1. The number of occupied electron shells increases down the group.
2. The shielding effect of inner electrons increases.
3. The outermost electrons become farther from the nucleus, so the ionic radius increases.

Therefore: Ionic radius increases down a group.

Q. Explain the variation of ionic radius down a group with an example.

Solution:

Ion	Relative Size	Reason
Li⁺	Smallest	Fewer electron shells
Na⁺	↑	One additional shell
K⁺	↑↑	More shells and shielding
Rb⁺	↑↑↑	Still more shells

Li⁺ < Na⁺ < K⁺ < Rb⁺

Q. Discuss the trend of ionic radius down a group and explain the factors responsible for it.

Solution:

Ionic radius generally increases as we move down a group in the periodic table. The following factors are responsible:

• Increase in principal quantum number: Each step down adds a new electron shell.
• Increase in shielding effect: Inner electrons increasingly shield the outer electrons from the nucleus.
• Increase in distance: The outermost electron shell lies farther from the nucleus.
• Reduced effective attraction: Although nuclear charge increases, the additional shells and shielding cause the outer electrons to experience weaker effective attraction.
• Hence, the overall ionic size increases down the group.

General Trend:

Li⁺ < Na⁺ < K⁺ < Rb⁺ < Cs⁺

Q. Explain in detail the trend of ionic radii down a group. Also explain the role of electron shells and shielding effect with a suitable example.

Detailed Solution:

The ionic radius is the effective size of an ion. It depends mainly on the number of occupied electron shells and the attraction between the nucleus and the electrons.

When we move down a group, the atomic number increases and a new principal energy level is added at each step. Therefore, the outermost electrons are located farther away from the nucleus.

Factor	Effect Down the Group
Number of shells	Increases
Shielding effect	Increases
Distance of outer shell from nucleus	Increases
Ionic radius	Increases

Example: Group 1 Cations

Li⁺ → Na⁺ → K⁺ → Rb⁺ → Cs⁺

Ionic radius increases from Li⁺ to Cs⁺.

For example, Li⁺ has electrons only in the first shell, while Na⁺ has electrons up to the second shell and K⁺ has electrons up to the third shell. Thus, the outer electron shell is progressively farther from the nucleus.

The inner-shell electrons also shield the outer electrons from the full positive charge of the nucleus. This shielding effect increases down the group and contributes to the increase in ionic size.

🎯 Final Answer:

The ionic radius generally increases down a group because successive elements have additional electron shells and greater shielding effect. These factors increase the distance of the outermost electrons from the nucleus, resulting in a larger ionic radius.

Down the group ↓ → Number of shells ↑ → Shielding ↑ → Ionic radius ↑

🎯 Quick Revision

Down a Group ↓
Electron shells ↑
Shielding effect ↑
Distance from nucleus ↑
Ionic Radius ↑

Example:
Li⁺ < Na⁺ < K⁺ < Rb⁺ < Cs⁺