Class 10 Science – Chapter 3
Ionic Compounds
आयनिक यौगिक | Formation, Sodium Chloride & Properties
1. How are Ionic Compounds Formed?
Ionic compounds are formed by the transfer of electrons from one atom to another. Usually, a metal loses one or more electrons to form a positive ion (cation), while a non-metal gains electrons to form a negative ion (anion).
आयनिक यौगिक इलेक्ट्रॉनों के एक परमाणु से दूसरे परमाणु में स्थानांतरण द्वारा बनते हैं। सामान्यतः धातु एक या अधिक इलेक्ट्रॉन खोकर धनायन बनाती है, जबकि अधातु इलेक्ट्रॉन ग्रहण करके ऋणायन बनाती है।
Formation of Ions / आयनों का निर्माण
A neutral atom has equal numbers of protons and electrons. When an atom loses or gains electrons, it becomes an ion.
उदासीन परमाणु में प्रोटॉन और इलेक्ट्रॉनों की संख्या समान होती है। इलेक्ट्रॉन खोने या प्राप्त करने पर परमाणु आयन बन जाता है।
Cation / धनायन
Sodium loses one electron and forms Na⁺.
Anion / ऋणायन
Chlorine gains one electron and forms Cl⁻.
Electrostatic Attraction
The oppositely charged Na⁺ and Cl⁻ ions attract each other strongly through electrostatic force. This attraction forms an ionic bond.
विपरीत आवेश वाले Na⁺ और Cl⁻ आयन वैद्युतस्थैतिक आकर्षण द्वारा एक-दूसरे को मजबूती से आकर्षित करते हैं। यही आकर्षण आयनिक बंध बनाता है।
Ionic bond = Strong electrostatic attraction between oppositely charged ions.
आयनिक बंध = विपरीत आवेश वाले आयनों के बीच प्रबल वैद्युतस्थैतिक आकर्षण।
2. Formation of Sodium Chloride (NaCl)
Sodium chloride is formed by the transfer of one electron from sodium atom to chlorine atom.
सोडियम क्लोराइड का निर्माण सोडियम परमाणु से क्लोरीन परमाणु में एक इलेक्ट्रॉन के स्थानांतरण से होता है।
Step 1: Electronic Configuration of Sodium
Sodium (Na) has atomic number 11.
Sodium has one electron in its outermost shell. It tends to lose this electron to achieve a stable configuration.
Step 2: Formation of Sodium Ion
After losing one electron:
Sodium becomes a positively charged ion called sodium ion.
Step 3: Electronic Configuration of Chlorine
Chlorine has atomic number 17.
Chlorine needs one electron to complete its outermost shell.
Step 4: Formation of Chloride Ion
After gaining one electron:
Step 5: Formation of NaCl
The Na⁺ and Cl⁻ ions are held together by strong electrostatic attraction.
Na → Na⁺ + e⁻
Cl + e⁻ → Cl⁻
Therefore:
Na⁺ + Cl⁻ → NaCl
Why is NaCl electrically neutral?
Na⁺ has +1 charge and Cl⁻ has −1 charge. Therefore, the total charge is zero.
Hence NaCl is electrically neutral.
3. Properties of Ionic Compounds
Ionic compounds have characteristic physical and chemical properties because their ions are held together by strong electrostatic forces.
आयनिक यौगिकों में विशेष भौतिक एवं रासायनिक गुण होते हैं क्योंकि उनके आयन मजबूत वैद्युतस्थैतिक बलों द्वारा जुड़े रहते हैं।
1. Physical State
Ionic compounds are generally hard and crystalline solids at room temperature.
आयनिक यौगिक सामान्यतः कमरे के तापमान पर कठोर एवं क्रिस्टलीय ठोस होते हैं।
2. High Melting and Boiling Points
They have high melting and boiling points because strong electrostatic forces exist between oppositely charged ions.
इनके गलनांक और क्वथनांक अधिक होते हैं क्योंकि विपरीत आवेशित आयनों के बीच प्रबल आकर्षण बल होता है।
3. Solubility in Water
Many ionic compounds are soluble in water. Water can separate and surround the ions.
कई आयनिक यौगिक जल में घुलनशील होते हैं। जल आयनों को अलग करके उन्हें घेर सकता है।
4. Electrical Conductivity
Solid ionic compounds generally do not conduct electricity because their ions cannot move freely.
ठोस अवस्था में आयनिक यौगिक सामान्यतः विद्युत का चालन नहीं करते क्योंकि आयन स्वतंत्र रूप से गति नहीं कर सकते।
When molten or dissolved in water, their ions become mobile and they conduct electricity.
Solid ionic compound → Generally does not conduct electricity.
Molten ionic compound → Conducts electricity.
Aqueous solution → Generally conducts electricity.
5. Brittle Nature
Ionic crystals are brittle. When layers of ions shift, similarly charged ions can come close together and repel each other, causing the crystal to break.
6. Crystalline Structure
Ionic compounds have an ordered arrangement of positive and negative ions in a crystal lattice.
यह केवल एक सरल representation है; वास्तविक ionic crystal में ions का तीन-आयामी नियमित lattice arrangement होता है।
4. Electron Transfer & Ion Formation
Why do atoms form ions?
Atoms tend to attain a more stable electronic configuration. Metals generally lose electrons, while non-metals generally gain electrons.
परमाणु अधिक स्थायी इलेक्ट्रॉनिक विन्यास प्राप्त करने की प्रवृत्ति रखते हैं। धातुएँ सामान्यतः इलेक्ट्रॉन खोती हैं और अधातुएँ इलेक्ट्रॉन ग्रहण करती हैं।
Example: Magnesium Chloride
Magnesium has atomic number 12:
It loses two electrons:
Each chlorine atom gains one electron:
Therefore, one Mg atom combines with two Cl atoms:
Valency Concept
Na has valency 1 and Cl has valency 1, therefore formula is NaCl.
Mg has valency 2 and Cl has valency 1, therefore formula is MgCl₂.
The total positive charge must equal the total negative charge in an ionic compound.
Examples
5. Melting Point, Boiling Point & Solubility
High Melting Point
A large amount of energy is needed to overcome the strong attraction between ions. Hence ionic compounds generally have high melting points.
High Boiling Point
Similarly, a large amount of energy is needed to separate ions completely, so ionic compounds generally have high boiling points.
Why do solid ionic compounds not conduct electricity?
Why do molten ionic compounds conduct electricity?
Why do aqueous solutions conduct electricity?
When an ionic compound dissolves in water, its ions become mobile and can carry charge.
Solubility
Many ionic compounds dissolve in water, but not every ionic compound is soluble. Solubility depends on the balance between ion-ion attractions in the crystal and ion-water interactions.
Ionic compounds conduct electricity in molten state or aqueous solution because ions are free to move.
30 MCQs – Ionic Compounds
Answer: B. Transfer of electrons
Electron transfer produces oppositely charged ions.
Answer: C. Na⁺
Sodium loses one electron.
Answer: B. Cl⁻
Answer: B. 11
Answer: B. 2,8,1
Answer: A. 2,8,7
Answer: B. NaCl
Answer: B. Ionic
Answer: B. Losing one electron
Answer: B. Gaining one electron
Answer: B. Hard crystalline solids
Answer: B. High melting points
Answer: B. Strong electrostatic forces
Answer: B. Ions are fixed in the lattice
Answer: B. Ions can move freely
Answer: B. Ions are mobile
Answer: B. Cation
Answer: C. Anion
Answer: B. Mg²⁺
Answer: B. MgCl₂
Answer: A. NaCl
Answer: B. Electrostatic
Answer: A. Brittle
Answer: B. Molten
Answer: C
Answer: C. 0
Answer: C. Al³⁺
Answer: B. Al₂O₃
Answer: A. Metal and non-metal
Answer: B
30 Subjective Questions – Complete Solutions
1 Mark Questions
आयनिक यौगिक विपरीत आवेश वाले आयनों से बना यौगिक है, जो वैद्युतस्थैतिक आकर्षण से जुड़े रहते हैं।
2 Mark Questions
Na → Na⁺ + e⁻
Thus Na⁺ has the stable configuration 2,8.
Cl + e⁻ → Cl⁻
Thus Cl⁻ has the stable configuration 2,8,8.
3 Mark Questions
Na → Na⁺ + e⁻
Cl has configuration 2,8,7 and gains one electron:
Cl + e⁻ → Cl⁻
Then:
Na⁺ + Cl⁻ → NaCl
Mg → Mg²⁺ + 2e⁻
Two chlorine atoms each gain one electron:
2Cl + 2e⁻ → 2Cl⁻
Therefore:
Mg²⁺ + 2Cl⁻ → MgCl₂
2. They have high melting and boiling points.
3. They conduct electricity in molten state or aqueous solution.
4 Mark Questions
Na = 2,8,1
Na → Na⁺ + e⁻
Chlorine:
Cl = 2,8,7
Cl + e⁻ → Cl⁻
The ions attract:
Na⁺ + Cl⁻ → NaCl
Thus an ionic bond is formed.
Total charge:
(+1) + (−1) = 0
Therefore NaCl is electrically neutral.
In molten state or aqueous solution, ions become mobile and carry electric charge. Therefore they conduct electricity in these states.
Anion: Negatively charged ion formed by gain of electrons. Example: Cl⁻, O²⁻.
5 Mark Questions
Na → Na⁺ + e⁻
Chlorine has atomic number 17 and configuration 2,8,7. It gains one electron:
Cl + e⁻ → Cl⁻
The resulting ions have stable electronic configurations.
Na⁺ and Cl⁻ attract each other:
Na⁺ + Cl⁻ → NaCl
The strong electrostatic attraction between these ions is called an ionic bond.
2. Crystalline: Ions have an ordered lattice arrangement.
3. High melting point: Strong electrostatic attraction requires high energy to overcome.
4. Brittle: Shifting layers bring like charges close and cause repulsion.
5. Electrical conduction: They conduct electricity in molten or aqueous state because ions can move.
Mg = 2,8,2
It loses two electrons:
Mg → Mg²⁺ + 2e⁻
Each chlorine atom gains one electron:
2Cl + 2e⁻ → 2Cl⁻
Therefore:
Mg²⁺ + 2Cl⁻ → MgCl₂
Thus MgCl₂ is an ionic compound.
In the solid state, however, ions are held at fixed positions and cannot move freely. Therefore solid ionic compounds generally do not conduct electricity.
In molten NaCl, the ions become free to move.
Moving ions carry electric charge, so molten NaCl conducts electricity.
6 Mark Questions
Na = 2,8,1
Step 2: Sodium loses one electron:
Na → Na⁺ + e⁻
Na⁺ = 2,8
Step 3: Chlorine has atomic number 17:
Cl = 2,8,7
Step 4: Chlorine gains one electron:
Cl + e⁻ → Cl⁻
Cl⁻ = 2,8,8
Step 5: The oppositely charged ions attract:
Na⁺ + Cl⁻ → NaCl
This electrostatic attraction forms the ionic bond. The resulting compound is electrically neutral.
1. Hardness: Strong electrostatic forces make them hard.
2. High melting and boiling points: Large energy is needed to overcome ionic attraction.
3. Crystalline nature: Ions are arranged regularly.
4. Brittleness: Displacement of layers brings like charges together and causes repulsion.
5. Electrical conductivity: Ions conduct electricity when free to move in molten or aqueous state.
Molten: Ions are mobile; electrical conduction occurs.
Aqueous: Ions are dispersed/mobile in solution; electrical conduction generally occurs.
Example:
NaCl(aq) → Na⁺(aq) + Cl⁻(aq)
Al → Al³⁺ + 3e⁻
Oxygen has configuration 2,6 and each oxygen atom gains two electrons:
O + 2e⁻ → O²⁻
To balance electrons:
2Al → 2Al³⁺ + 6e⁻
3O + 6e⁻ → 3O²⁻
Therefore:
2Al³⁺ + 3O²⁻ → Al₂O₃
Hence the formula is Al₂O₃.
1. Not every ionic compound is soluble in water. Solubility depends on the nature of the compound and the balance of lattice and hydration interactions.
2. Ionic compounds generally do not conduct electricity in solid state because their ions are fixed in the crystal lattice.
3. They generally conduct electricity when molten or dissolved in water because their ions can move.
Therefore, the correct statement is:
“Ionic compounds generally conduct electricity in molten or aqueous state, not in the solid state.”
Formation + NaCl + Properties + Electron Transfer + 30 MCQs + 30 Subjective Questions
