JEE Advanced · Chemistry
Prepare for current JEE Advanced Solid State by connecting lattice description, unit-cell counting, packing geometry, nearest neighbours, radius-ratio model, density and point defects.
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In short
Solid State is listed in JEE Advanced 2026 and is not listed in JEE Main 2026 Chemistry.
Solve it by identifying the crystal system and cell, counting the fraction of each lattice point owned by the unit cell, determining geometry and nearest neighbours, applying the correct radius or density relation, and then classifying any defect by what leaves, moves, or occupies a new site.
The official JEE documents define content scope. They do not publish chapter weightage, so none is asserted here.
Verified against the current JEE Main 2026 and JEE Advanced 2026 syllabus documents on 8 September 2026. Solid State is an Advanced-only current-syllabus page, not a separate JEE Main 2026 unit.
Sources: JEE Main 2026 syllabus and JEE Advanced 2026 syllabus, both linked in the sources section below.
Prerequisite
Mole Concept
Count particles using Avogadro's constant before computing density or packing fraction.
Prerequisite
Chemical Bonding
Distinguish bonding types that determine lattice character before applying a packing model.
Prerequisite
Periodic Table
Ionic radii used in the radius-ratio model come from periodic trends.
Parent
JEE Chemistry
Subject hub for the Chemistry chapter set.
This is a readiness check, not a weightage or scoring-priority list.
Crystalline solids have long-range periodic order in the ideal model; amorphous solids do not.
Crystalline solids have long-range periodic order in the ideal model. Amorphous solids lack that long-range periodicity, so unit-cell counting and packing relations do not apply to them.
Use edge lengths a, b, c and angles alpha, beta, gamma to identify the crystal system. The seven crystal systems are distinguished only by these edge and angle relations.
Corner, edge, face and body positions contribute different fractions to a selected unit cell.
Corner, edge, face, and body positions contribute different fractions to a selected unit cell. Counting visible spheres rather than owned fractions is the most common source of error in this chapter.
The direction along which particles touch produces the correct edge-radius relation: cube edge for simple cubic, body diagonal for bcc, and face diagonal for fcc.
Coordination number counts nearest neighbours around a particle; Z counts effective particles per unit cell.
Coordination number counts nearest neighbours around a particle. Z counts effective particles per unit cell. These are different quantities and must not be substituted for each other.
Density, packing efficiency, or radius ratio follows only after cell type and assumptions are fixed. Applying a formula before fixing the cell type is a decision error.
Ask whether particles are missing, displaced to interstitial sites, substituted, or accompanied by electronic compensation before naming a defect or predicting its density effect.
Match the question signal to the first model and its required check.
These intervals are geometric guides, not universal experimental laws. Polarisation, bonding character, pressure, and the selected ionic-radius convention can affect real structures.
Schottky requires a structure that can sustain paired vacancies; Frenkel is a vacancy-and-interstitial pair, not an added impurity.
A corner contributes one eighth, an edge one quarter, a face one half, and a body position one whole particle to the unit cell.
Fraction of a lattice position owned by one conventional unit cell.
Use when — Counting the effective number of particles per unit cell (shared-cell bookkeeping).
Common trap — Counting visible spheres rather than owned fractions.
Z equals 1 for simple cubic, 2 for body-centred cubic, and 4 for face-centred cubic.
Effective lattice points per conventional cubic cell.
Use when — The lattice is a monatomic lattice-point model of the stated cubic type.
Common trap — Confusing Z with coordination number.
For simple cubic, the edge length equals twice the particle radius.
Contact along the cube edge for simple cubic packing.
Use when — The lattice is simple cubic under the hard-sphere contact model.
Common trap — Using this relation for bcc or fcc.
For body-centred cubic, root three times the edge length equals four times the particle radius.
Contact along the body diagonal for body-centred cubic packing.
Use when — The lattice is body-centred cubic under the ideal hard-sphere model.
Common trap — Using the face diagonal instead of the body diagonal.
For face-centred cubic, root two times the edge length equals four times the particle radius.
Contact along the face diagonal for face-centred cubic packing.
Use when — The lattice is face-centred cubic under the ideal hard-sphere model.
Common trap — Using the body diagonal instead of the face diagonal.
Density equals Z times molar mass divided by the Avogadro constant times unit-cell volume.
Unit-cell density.
Use when — Z, formula units or particles match the molar-mass basis used.
Common trap — Mixing pm, cm, and m within the same calculation.
Packing efficiency equals Z times the sphere volume, divided by the cell volume, expressed as a percentage.
Packing efficiency for equal hard spheres in a given cell.
Use when — The spheres are equal and the correct cell relation for the lattice is used.
Common trap — Substituting the wrong Z or radius relation for the lattice type.
Radius ratio equals the cation radius divided by the anion radius.
Radius ratio used as an ideal coordination guide.
Use when — Ions are treated as hard spheres with specified radii.
Common trap — Using the standard threshold ranges as absolute structure predictions.
Answer: Density ≈ 6.64 g/cm^3, with fcc meaning Z = 4, molar mass per mole of atoms, and length and density units kept compatible.
For fcc, Z = 4 atoms per conventional cell.
Convert the edge: 400 pm = 4.00 × 10^-8 cm.
Cell volume is a^3 = (4.00 × 10^-8)^3 = 6.40 × 10^-23 cm^3.
Cell mass is ZM/N_A = (4 × 64.0) / (6.022 × 10^23) = 4.25 × 10^-22 g.
Density is 4.25 × 10^-22 / 6.40 × 10^-23 = 6.64 g/cm^3 to three significant figures.
Calling Solid State a current Main 2026 Chemistry chapter.
Needs reviewWhy it happens
The official JEE Main 2026 Chemistry syllabus has no Solid State unit.
How it is corrected
Check the official syllabus mapping table on this page before assuming Main-exam relevance.
Counting every corner or face particle as fully inside one cell.
Knowledge gapWhy it happens
Corner, edge, and face positions are shared between multiple cells, so only a fraction belongs to any one cell.
How it is corrected
Apply the fractional-ownership table before summing particles per cell.
Confusing coordination number with Z.
Recall gapWhy it happens
Coordination number counts nearest neighbours; Z counts effective particles per unit cell. They are unrelated quantities.
How it is corrected
Separate the two questions explicitly before substituting either into a formula.
Using the fcc radius relation for bcc.
Decision / selection errorWhy it happens
Each lattice type has particles touching along a different diagonal or edge.
How it is corrected
Identify the lattice type first, then select the matching contact-geometry relation.
Mixing picometres with centimetres inside a density calculation.
Execution errorWhy it happens
Density calculations combine length cubed with mass; any length-unit inconsistency propagates directly into the result.
How it is corrected
Convert every length to one consistent unit before cubing it for cell volume.
Quoting packing efficiencies without the ideal hard-sphere condition.
Knowledge gapWhy it happens
The standard packing results (about 74% for fcc and hcp, about 68% for bcc) hold for ideal monatomic hard-sphere structures, not every real solid.
How it is corrected
State the hard-sphere assumption whenever a packing-efficiency number is used.
Treating radius-ratio intervals as exact structure predictions.
Decision / selection errorWhy it happens
Polarisation, bonding character, pressure, and the ionic-radius convention used can affect real structures beyond the ideal guide.
How it is corrected
Use the radius-ratio table as a guide, and check it against the actual reported structure.
Saying every vacancy lowers density without checking whether an ion leaves the crystal.
Decision / selection errorWhy it happens
Schottky defects remove ions and lower density, but Frenkel defects keep the ion inside the crystal, so density is approximately unchanged.
How it is corrected
Check the point-defect ledger for the specific defect before predicting a density change.
Confusing a Frenkel interstitial with an added impurity particle.
Recall gapWhy it happens
A Frenkel defect is a displaced ion of the same species, not an added foreign species.
How it is corrected
Confirm whether the interstitial particle is the same species as the lattice or a different species before naming the defect.
FAQ
Straight answers about how Rank Sarthi fits into serious exam preparation.
No. It is not listed in the official JEE Main 2026 Chemistry syllabus.
Yes. Its official scope includes crystal systems, close packing, fcc, bcc, hcp, nearest neighbours, radius ratio, and point defects.
Z is the effective number of particles or formula units in a selected unit cell. Coordination number is the number of nearest neighbours around a particle.
No. Weightage, trend percentages and question-count forecasts are deliberately not published on this page.
Evidence boundary: this page states plainly that Solid State is absent from the current JEE Main 2026 Chemistry syllabus and present in the current JEE Advanced 2026 syllabus. Crystal-system, unit-cell, packing, radius-ratio and defect content follows NCERT curriculum and exemplar material. No chapter weightage, question frequency or forecast is asserted, and no current-Main relevance module is implied.
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