Ch 6Solid State — Class 12 Chemistry, concept-first.

Look around you and you'll find far more solids than liquids or gases -- most of what you touch, use and build with is solid matter, held in a definite shape and volume because its atoms, ions or mole…

Matter exists in three physical states -- solid, liquid and gas -- and of the three, solids are what we meet most often in daily life.

Every solid can be sorted into one of two broad classes based purely on how its constituent particles are arranged:

Having split solids broadly into crystalline and amorphous, the unit now looks specifically at the four families of crystalline solid distinguished by the type of bonding holding their constituent par…

The structural units of an ionic crystal are cations and anions, bound together by strong electrostatic (Coulombic) attractive forces.

In a covalent (network) solid, the constituent atoms are bound together in a continuous three-dimensional network entirely by covalent bonds -- there are no separate 'molecules' at all; the whole crys…

In a molecular solid, the constituent particles are neutral molecules, held together only by the comparatively weak van der Waals force.

Metallic bonding, studied already in Class XI, gives metallic solids their own distinct structure: the lattice points are occupied by positive metal ions, while a 'cloud' or 'sea' of delocalised (mobi…

A crystalline solid is characterised by a definite orientation of its atoms, ions or molecules relative to one another, extending as a regular three-dimensional pattern throughout the whole solid.

Unit cells come in two basic kinds. A primitive unit cell contains only one type of lattice point -- lattice points sitting solely at the 8 corners of the cell, with nothing extra inside or on a face.…

In the simple (primitive) cubic unit cell, an identical atom, ion or molecule occupies every one of the cube's 8 corners.

In the body-centred cubic (bcc) unit cell, an identical particle occupies every corner, AND one additional atom sits exactly at the body centre of the cube.

In the face-centred cubic (fcc) unit cell, identical atoms sit at every one of the 8 corners AND at the centre of every one of the 6 faces.

Because it is not practical to draw or directly measure a three-dimensional crystal lattice at the atomic scale, the actual dimensions of a unit cell are worked out indirectly, using X-ray diffraction…

Once the number of atoms per unit cell (n) and the edge length (a) of a cubic unit cell are known, the crystal's density follows directly from the basic definition of density as mass over volume, appl…

A fruit stall displaying fruit in a closest-packed pile -- each fruit nestled into the depression formed by the fruits below it -- is a familiar, everyday picture of what this section formalises: how…

In any one specific direction, there is only a single possible way to arrange identical spheres: a simple touching row, with each sphere in contact with exactly two neighbouring spheres, one on either…

A two-dimensional planar layer can be built from one-dimensional rows in exactly two distinct ways:

Stacking the AAA... two-dimensional layer directly on top of itself, layer after layer -- so that every sphere in one layer sits exactly on top of the sphere immediately below it, with all layers perf…

In the body-centred cubic (bcc) arrangement, the spheres of the first layer (A-type) are slightly separated from one another, and the second layer is formed by placing its spheres into the depressions…

Forming the first and second layers. The first close-packed layer is built exactly as in the 2D ABAB...

The internal structure an ionic compound actually adopts depends on both its stoichiometry and the relative sizes of its ions.

No real crystal is perfect -- the law of nature guarantees that every crystal carries some defects in the arrangement of its constituent particles.

Schottky defect arises when equal numbers of cations and anions go missing from the crystal lattice. Because a cation vacancy and an anion vacancy always appear together in matched pairs, this defect…

Frenkel defect arises when an ion is dislodged from its normal lattice position and instead relocates to occupy an interstitial position elsewhere in the structure -- rather than leaving the crystal a…

Metal excess defect arises when a crystal contains more metal ions (cations) than anions. It is seen in the alkali metal halides, such as NaCl and KCl.

Metal deficiency defect arises when a crystal contains fewer cations than the number of anions would normally require.

A general and deliberate way of introducing point defects into an ionic solid is by adding impurity ions.

This chapter-end exercise checks the full span of Unit 6. The 23 'Choose the Best Answer' multiple-choice questions cover: distinguishing covalent, ionic, molecular and metallic solids and correctly c…

Sample papers and previous-year board questions for this subject.