SOLID STATE
Class 12 Chemistry | Chapter Notes with Mnemonics, Numericals and Practice
Set
Original study notes written from the NCERT syllabus.
CBSE Boards • JEE Main • NEET
No. Topic
1 Understanding solids and their classification
2 Lattice, unit cell and the 7 crystal systems
3 Z, edge length and density numericals
4 Close packing and voids
5 Packing efficiency (SC, BCC, FCC)
6 Ionic solid structures and radius ratio
7 Imperfections in solids
8 Electrical properties and band theory
9 Magnetic properties (+ dielectric bonus)
10 Formula sheet, mixed practice set and drawing checklist
Solid State | Class 12 Chemistry Notes Page 1
, SECTION 1
Understanding Solids
1.1 What is a solid?
In a solid, the constituent particles (atoms, ions or molecules) stay fixed in position and only vibrate
about their mean positions. That is why a solid has a definite shape and a definite volume. The
intermolecular distances are small and the forces are strong.
1.2 Crystalline vs Amorphous solids
Property Crystalline Amorphous
Arrangement Long-range order Only short-range order
Melting Sharp melting point Softens gradually over a range of temperature
Cutting Breaks along clean, flat surfaces Breaks along irregular surfaces
Properties Anisotropic (vary with direction) Isotropic
Type True solid Pseudo solid / supercooled liquid
Heat of fusion Definite Not definite
Examples NaCl, quartz, diamond Glass, rubber, plastic, quartz glass
Memory trick
Crystal = Consistent order. Amorphous = All over the place.
Quartz and quartz glass are both SiO2. Quartz is crystalline, quartz glass is amorphous. This is a frequent exam
example.
1.3 Four types of solids by bonding
Type Particles Force Properties Examples
Molecular Molecules London / Soft, low m.p., insulator Ar, I2, dry ice (non-polar);
dipole-dipole / HCl (polar); ice
H-bond (H-bonded)
Ionic Cations + Electrostatic Hard, brittle, high m.p.; NaCl, MgO, KCl
anions insulator as solid, conductor
when molten/aqueous
Metallic Kernels + sea Metallic bond Conductor, malleable, Cu, Fe, Ag
of electrons ductile, lustrous
Covalent Atoms Giant network of Very hard, very high m.p., Diamond, SiC, SiO2
(network) covalent bonds insulator
Mnemonic: M-I-M-C
Molecular (soft) → Ionic (brittle) → Metallic (malleable) → Covalent (giant).
Frequently asked exceptions
Graphite: a covalent solid that is soft and conducts electricity. Each C is sp2, 3 electrons form bonds and the 4th is
delocalised between the layers. The layers are held by weak van der Waals forces, so graphite is soft.
Diamond: each C is sp3 and all four electrons are used in bonds, so there is no free electron and it does not
conduct. It is the hardest natural substance.
Ice: a molecular solid, but hydrogen bonding gives it a relatively high m.p. for its category.
1.4 Practice questions
Solid State | Class 12 Chemistry Notes Page 2
Class 12 Chemistry | Chapter Notes with Mnemonics, Numericals and Practice
Set
Original study notes written from the NCERT syllabus.
CBSE Boards • JEE Main • NEET
No. Topic
1 Understanding solids and their classification
2 Lattice, unit cell and the 7 crystal systems
3 Z, edge length and density numericals
4 Close packing and voids
5 Packing efficiency (SC, BCC, FCC)
6 Ionic solid structures and radius ratio
7 Imperfections in solids
8 Electrical properties and band theory
9 Magnetic properties (+ dielectric bonus)
10 Formula sheet, mixed practice set and drawing checklist
Solid State | Class 12 Chemistry Notes Page 1
, SECTION 1
Understanding Solids
1.1 What is a solid?
In a solid, the constituent particles (atoms, ions or molecules) stay fixed in position and only vibrate
about their mean positions. That is why a solid has a definite shape and a definite volume. The
intermolecular distances are small and the forces are strong.
1.2 Crystalline vs Amorphous solids
Property Crystalline Amorphous
Arrangement Long-range order Only short-range order
Melting Sharp melting point Softens gradually over a range of temperature
Cutting Breaks along clean, flat surfaces Breaks along irregular surfaces
Properties Anisotropic (vary with direction) Isotropic
Type True solid Pseudo solid / supercooled liquid
Heat of fusion Definite Not definite
Examples NaCl, quartz, diamond Glass, rubber, plastic, quartz glass
Memory trick
Crystal = Consistent order. Amorphous = All over the place.
Quartz and quartz glass are both SiO2. Quartz is crystalline, quartz glass is amorphous. This is a frequent exam
example.
1.3 Four types of solids by bonding
Type Particles Force Properties Examples
Molecular Molecules London / Soft, low m.p., insulator Ar, I2, dry ice (non-polar);
dipole-dipole / HCl (polar); ice
H-bond (H-bonded)
Ionic Cations + Electrostatic Hard, brittle, high m.p.; NaCl, MgO, KCl
anions insulator as solid, conductor
when molten/aqueous
Metallic Kernels + sea Metallic bond Conductor, malleable, Cu, Fe, Ag
of electrons ductile, lustrous
Covalent Atoms Giant network of Very hard, very high m.p., Diamond, SiC, SiO2
(network) covalent bonds insulator
Mnemonic: M-I-M-C
Molecular (soft) → Ionic (brittle) → Metallic (malleable) → Covalent (giant).
Frequently asked exceptions
Graphite: a covalent solid that is soft and conducts electricity. Each C is sp2, 3 electrons form bonds and the 4th is
delocalised between the layers. The layers are held by weak van der Waals forces, so graphite is soft.
Diamond: each C is sp3 and all four electrons are used in bonds, so there is no free electron and it does not
conduct. It is the hardest natural substance.
Ice: a molecular solid, but hydrogen bonding gives it a relatively high m.p. for its category.
1.4 Practice questions
Solid State | Class 12 Chemistry Notes Page 2
