Ch 1Solid State — Class 12 Chemistry, concept-first.

The solid state is one of the three common states of matter, and it stands apart from liquids and gases because the particles that make up a solid -- atoms, ions or molecules -- are held together by s…

Solids are broadly divided into two types depending on how their constituent particles are arranged: crystalline solids and amorphous solids.

Crystalline solids possess three characteristic properties that set them apart. First, there is regularity and periodicity in the arrangement of their constituent particles, with this ordered arrangem…

Amorphous solids lack the long-range order of crystalline solids. Their constituent particles are randomly arranged and possess, at best, a short-range order -- essentially they behave like supercoole…

Similarities and differences in crystal structure across substances are described by two related terms.

Crystalline solids are further classified into four broad categories based on the nature of the constituent particles and the type of force holding them together: ionic solids, covalent network solids…

Ionic crystals have the following characteristics:

Characteristics of covalent network crystals are as follows:

Substances such as , , , and give molecular crystals on solidification, and crystalline organic compounds are molecular solids as well. Their characteristics:

Metallic crystals are crystalline solids formed by atoms of the same metallic element, held together by a metallic bond.

The ordered, three-dimensional arrangement of particles within a crystal is described using two linked ideas: the lattice and the basis.

A lattice is a geometrical arrangement of points in a three-dimensional periodic array -- purely a mathematical scaffold of positions, with no physical particle yet attached to it.

The space lattice of a crystal is built up by repeating a three-dimensional basic pattern; this smallest repeating structural unit of a crystalline solid is called the unit cell.

There are four types of unit cell, distinguished by where the constituent particles are located within the cell.

Mathematical analysis shows that only fourteen distinct kinds of three-dimensional space lattice are geometrically possible -- there are just 14 ways in which identical points can be arranged in a per…

In the cubic crystal system all three edge lengths are equal () and all three interaxial angles are . The cubic system has three possible kinds of unit cell:

The number of particles that actually belong to a given unit cell depends on how each particle is shared with the neighbouring cells.

The relationship between the density of a substance, its molar mass and its unit cell edge length is deduced in the following steps.

The constituent particles of a crystalline solid are close packed -- they are arranged as tightly together as possible, which maximises the attractive interactions between neighbouring particles.

The three-dimensional close packed structure is best understood by building it up in stages: first a single row of spheres, then a layer, then a stack of layers.

The coordination number of a sphere in a close packed structure -- the number of neighbouring spheres it touches -- depends on which structure the layers build:

The tetrahedral and octahedral voids created during hexagonal close packing occur in a fixed proportion to the number of particles packed.

Just like coordination number, packing efficiency gives a quantitative measure of how tightly the particles of a crystal are packed.

The packing efficiency of a metal crystal in the simple cubic lattice is obtained by the following steps.

The packing efficiency of a metal crystal in the body-centred cubic lattice is obtained by the same four steps.

The packing efficiency of a metal crystal in the face-centred cubic lattice (which equals that of the ccp and hcp lattices) is obtained by the same four steps.

Combining the density relation (Eq. 1.4) with Avogadro's number lets us count the particles -- and the unit cells -- present in any given mass of a metallic crystal.

Real, naturally occurring crystalline substances never have a perfect crystal structure -- they always show some disorder or irregularity in how their constituent particles are stacked, and such irreg…

Point defects are irregularities produced in the arrangement of the basis at the lattice points of a crystalline solid -- localised disruptions confined to individual lattice sites, as opposed to defe…

In a stoichiometric point defect the stoichiometry of the compound -- the ratio of atoms, or of cations to anions, fixed by its chemical formula -- remains unchanged even though the crystal is imperfe…

An impurity defect arises when foreign atoms -- atoms different from those of the host -- are present in the crystal lattice. There are two kinds.

In a nonstoichiometric defect the ratio of the atoms -- or of the cations to the anions -- genuinely becomes different from the ratio indicated by the compound's chemical formula, though the overall c…

Solids show an extremely wide range of electrical conductivity, and on this basis they are classified into three categories.

Band theory explains the electrical properties of solid metals, nonmetals and metalloids in terms of bands -- vast numbers of closely spaced electronic energy levels.

Metals are good conductors of electricity because the outermost electrons of all the atoms in the metallic crystal occupy the conduction band, and the number of electrons in that band is enormous.

In an insulator, the valence band is completely filled with electrons while the conduction band above it is entirely empty, and the two bands are separated by a large energy gap called the forbidden z…

A semiconductor's electrical conductivity is intermediate between that of a metal and that of an insulator; the metalloids silicon and germanium are the classic examples.

The conductivity of a semiconductor can be increased deliberately by doping -- adding a minute, controlled quantity of an impurity, called the dopant, to the pure material.

The magnetic properties of a solid follow from the classical picture of the spinning electron: a spinning electron behaves like a tiny magnet, its spin generating an induced magnetic field.

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