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3rd Proof, , , , , , , , 1 Introduction, , e Solid, liquid and gas are three physical, states of matter., , e Any state of matter can be changed into, another by affecting changes in conditions, of temperature and pressure., , * When sufficient energy is pumped into the, solid to overcome intermolecular forces of, attraction, it melts and transforms into, liquid state, liquids on heating to their, boiling points evaporate and transform into, gaseous state., , e The physical state of matter is the result of, interplay of intermolecular forces of, attrattion like dipole interactior, dipole-inc dipole interactic London, forces, hydrogen bonding, librium that exi:, , tates of matter is,, , , , Liqud = —— > Gas, — A (cool), , , , SA (Cool), , , , 1.2 Clas:, , Solids are two types:, [A] Crystalline Solids [B] Amorphous Solids., [A] Crystalline Solids:, , Definitions: A crystalline solid is a, homogeneous solid in which the, constituent particles, atoms, ions or, molecules are arranged in a definite, repeating pattern., , [B] Amorphous Solids: The substances, that appears like solids but do not have, well developed perfectly ordered, crystalline structure are called, amorphous solids (no form). E.g.: Tar,, glass, plastic, rubber and butter, etc., They are super cooled liquids. Regular, and periodically repeating pattern is, not observed. The structure is similar, to the structure of liquids., , cation of solids, , , , SOLID STATE, , ¢ Isomorphism and polymorphism :, , Similarity or dissimilarity in crystal, , structure of different solids is described as, , isomorphism and polymorphism., , (i) Isomorphism: Two or more substances, having the same crystal structure are, said to be isomorphous. Example (i), NaF and MgO (ii) NaNO, and CaCO, are, isomorphous pairs, and have the same, atomic ratios, 1:1 and 1:1:3, respectively,, of the constituent atoms., , (ii) Polymorphism: A single substance that, exists in two or more forms or, crystalline structures is said to be, polymorphous. Example : Calcite and, Argonite are two forms of calcium, carbonate; 4-quartz, B-quartz and, , férms of silica g, , , , , , ments is a py. Fo, xample: thfée_polymorphic.(allotropic), forms offea a are diamond? graphi, , , , and fullere, , , , [1.5. Classification of crystalline solids |, , , , (i) Ionic crystals: The constituent, particles are charged ions, Example : NaCl, K, SO, , CaF, , KCl, , (ii) Covalent network crystals: The, constituent particles in covalent, network solids are atoms., , Example: diamond, quartz (SiO, ), boron, nitride, carborandum are covalent, network solids., , (iii) Molecular crystals: The constituent, particles of molecular solids are molecules., Example : Cl, , CH, , H, , CO, , 0,, , (iv) Metallic crystals: These are crystalline, solids formed by atoms of the same, metallic element, held together by a, metallic bond., , Example: Na, K, Ca, Li., , @

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3rd Proof, , @, , , , lattices, , , , 1.4 Unit Cell and two three dimensional, , , , , , eA unit cell is the smallest repeating, , structural unit of a crystalline solid., , e When unit cells of the same crystalline, substance are repeated in space in all, directions, a crystalline solid is formed., , e Any point at the intersection of lines is called, , a lattice point., , ¢ The collection of all the points in the crystal, having similar environment is called space, , lattice., , e Shape of any crystal lattice depends upon, , the shape of the unit cell., , 1.5 Packing in solids, , e Incrystal lattice formed by simple cubic unit, cell, some space is occupied by constituent, particles while little space is unoccupied., , e This unoceuipied Space is called void., , e Unrysta, , , , particles a row, , e Thisconstitutes one dimensional arrangement, , of particles one after another. A planar two, , dimensional structure is obtained., , e In third stage, the planar arrangement of the, particles are extended to three dimensional, arrangement by placing planar layers one, , above the other., , 1.6 Density of unit cells, , , , Densiee Mass, ensity = Volume, _ 2xM, a®N ”, Mass of 1 unit cell = MZ, M =Mass A, Z =Number of atoms in the unit cell, a’ = Volume, , 1.7 Packing in voids of ionic solids, , e Ionic solids are formed from cations and, , anions., , , , ageconsists/of linearly arranged, , , , Reliable Series, , e Depending upon the size of cations and, anions of the ionic compounds, they either, occupy tetrahedral or octahedral hole of, crystal of lattice., , e¢ When cation size is small, it occupies, tetrahedral hole., , e When the cation size is bigger, it occupies, octahedral hole., , e When the cation size is very large, the, packing of anions are modified and are, separated from one another to accommodate, large cations in large cubic hole., , Fig. 1.1: Larger cation in large cubic hole, , e In cubic closed packed seep) 8 or hexagonal, , closed packed (hep) anior ava ara two, , rahed, , , , epetition of large’n, , e A perfect crystal has atoms or ions arranged, in a precise geometric order., , e Real gases are not perfect due to fault in, formation of crystal lattice., , e Big crytstals have some defects in arrangement, of constituent particles., , e When the crystallization occurs faster,, defects are more., , e The defects can be minimised by carrying out, crystallisation at the slowest rate., , e The crystal defects change the original, physical and chemical properties of crystalline, solids., , 1.9 Electrical Properties, , e Elemental solids are divided into metals, non, metals and metalloids., , e There are seventeen non metals placed at, the right side of the periodic table., , e Most of the non metals in periodic table are, separated from metals by metalloids like, boron, silicon, germanium, arsenic, tellurium,, polonium, astatine, etc.

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3rd Proof, , Chemistry — XII, , e There are seventeen metalloids., , e Metals are good conductors of heat and, electricity because of formation of metallic, bond consisting of positive ions in a sea of, delocalised mobile electrons., , e Non metals are poor conductors of heat and, , electricity due to absence of delocalised, , mobile electrons., , Metalloids are intermediate between metals, , and non metals., , e They are bad conductors of heat and, electricity but exhibit bright metallic lustre., , e They are not malleable and ductile but are, brittle., , E.g.: Boron, Silicon and Germanium., , ¢ Silicon is a semi conductor because it is, better conductor of electricity than non, metals but not as efficient as metals., , 1.10 Magnetic Properties, , Electrons revolve round the nucleus in, , VATIOUS~O < 1 alsoé t theifJéw, Chis ratesamagnet eld, spinning, , ror as tiny ts, NZEXT QUESTIONS |, , , , , , Can you recall?; (Textbook Pg. No. 1), , (1) What are the three most common states, of matter?, , Ans. The three common states of matter are solid,, liquid and gases., , (2) How does solid state differ from the other, two states? (Answer with reference to, volume, shape, effect of temperature and, pressure on these and the motion of, constituent particles and interparticle, forces.), , Ans. (i) The solid state of matter is characterised, by strong interparticle forces of attraction., , (ii) As a result most solids have definite shape, and volume, which change only slightly, with change in temperature and pressure., , (iii) The smallest constituent particles of, various solids are atoms, ions or, molecules., , , , , , ©, , Try this; (Textbook Pg. No. 1), , , , (3) B D, F, oOo °, Oo Oo °, o © o]o, ° o;oO, E A c, , , , , , , , Particle 1 O Particle 2, Observe the above figure carefully. The, two types of circles in this figure represent, two types of constituent particles of a solid., (i) Will you call the arrangement of, particles in this solid regular or, irregular?, (ii) Is the arrangement of constituent, particles same or different in, , diréctions’AB, (, 2 ) arrange I es i au, rystalline’ solid)., ii) Arrangement of tituent particle, Gifferent-in att d t, , eetions ‘du, , , , tropy., , Try This; (Textbook Pg. No. 3), , (4) Graphite is a covalent solid yet soft and, good conductor of electricity. Explain., Ans. (i) Graphite is soft because the layer of, carbon atoms in graphite can slide over, another layer., , Gi) Graphite has delocalised molecular, orbitals and the electrons in these, orbitals have the freedom to move in the, delocalised molecular orbital. Hence,, graphite is a good conductor of heat and, electricity., , Can you recall?; (Textbook Pg. No. 3), , (5) What are structures of diamond and, , graphite?, , Ans. (i) Graphite has a covalent structure in, which each carbon atom is joined to three, other carbon atoms by covalent bonds., , Gi) In the crystal lattice of diamond, each, carbon atom forms 4 bonds with adjacent, carbon atoms.

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3rd Proof, , (6) Name the bond that link carbon atoms, in diamond and graphite., , Ans. The carbon atoms in graphite and diamond, are linked by covalent bonds., , (7) Are all the valence electrons of carbon, atoms in graphite localized to specific, covalent bonds?, , Ans. (i) No. All the valence electrons of carbon, atoms in graphite are not localised to, specific covalent bonds., , (ii) The electrons in these orbitals have the, freedom to move in the delocalised, molecular orbital., , (iii) Hence, graphite is a good conductor of, heat and electricity., , Can you recall?; (Textbook Pg. No. 4), , (8) What is a hydrogen bond ?, , Ans. Hydrogen bond is defined as the chemical, bond formed between hydrogen atom and, any other electronegative atom. Example:, , , , , , , HEQHE!, tb Pg. No, r orbitals are formed., two atom als ?, , lecular orbita, , (10) What is metallic bond ?, Ans. Metallic bond is defined as the electrostatic, , attractive force between the metal and, conduction electrons., , Can you recall?; (Textbook Pg. No. 23), , (11) Let a small quantity of phosphorus be, , doped into pure silicon., , * Will the resulting material contain the, same number of total number of, electrons as the original pure silicon ?, , * Will the material be electrically, , neutral or charged ?, , Four of the five valence electrons of P, , are utilized in bonding the closest to four, , Si atoms. Thus, P has one extra electron, , than needed for bonding., , (ii) Therefore, Si doped with P has more, number of electrons in the conduction, band than those in the conduction band, in pure Si., , Ans. (i), , , , , , Reliable Series, , (iii)The conductivity of Si doped with P is, higher than that of pure Si. The, electrons in conduction band move, under the influence of an applied, potential and conduct electricity., , The material will be electrically neutral., , Use your brain power; (Textbook Pg. No. 13), , (12) Identify the arrangements A and B as, crystalline or amorphous., *, , ] -», +6, Ans. (A) Crystalline solids: since there is, regularity and periodicity in the, arrangement of constituent particles., (B) Amorphous solids: the constituent, , , , , , , particles aré rar, , Use your brain, , , , Aus. icc has the most efficient packing an, , the least efficient packing., Can you think?; (Textbook Pg. No. 20), , (14) When ZnO is heated it turns yellow and, returns back to original white colour on, cooling. What could be the reason ?, , Ans. ZnO is an example of non-stoichiometric, defect. In ZnO, Zn*? ions occupy the, interstitial sites. The electrons diffuse in the, crystal to occupy the interstitial sites., , Excess., , ©O© © ©, , neutral ——>, , @ © ©®e&, , Zn atom, , © © &®, ©eO@e, , Fig. 1.2 : (a) Neutral Zn atom at interstitial site

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3rd Proof, , Chemistry — XII, , ©, ©, @e,©, , @, Electron, , © ©.OO), © eee, , Fig. 1.2: (b) Zn** ions and electrons at interstitial site, , , , ZnO is white in colour but on heating it loses, oxygen and hence turns yellow and on cooling, it turns back to its original white color., , 1, Reaction: ZnO —> Zn*? + 9% + 2e, Can you recall?; (Textbook Pg. No. 20), (15) (i) What is electrical conductivity?, , Ans. It is the capacity of electric current to pass, through a material., , (ii) What is meant by the terms electrical, , , , , , ‘insulate id ‘semiye, A Insul, , conauct s, , Jhm~'m-saxre, , which do n, , through th, , , , nonmetals and molecular solids belong to, , this category., , Semiconductors: Solids having electrical, conductivities in the range 10“ to 104 Ohm, m7! are semiconductors. This range is, intermediate between conductors and, insulators. Metalloids like silicon,, germanium belong to this category., , *>—\ MULTIPLE CHOICE QUESTIONS, — (1 Mark each), , *(1) Molecular solids are, (a) crystalline solids (b) amorphous solids, (c) ionic solids (d) metallic solids, *(2) Which of the following is n-type, semiconductor?, (a) Pure Si (b) Si doped with As, (c) Si doped with Ga (d) Ge doped with In, *(3) In Frenkel defect,, , (a) electrical neutrality of the substance is, changed., (b) density of the substance is changed., , , , , , , , @, , (c) both cation and anion are missing., (d) overall electrical neutrality is preserved., , *(4) In crystal lattice formed by bec unit cell, the void volume is, (a) 68% (b) 74% (c) 32% (d)26%, , *(5) The coordination number of atoms in bcc, crystal lattice is, , (a) 2 (b) 4 (c) 6 (d) 8, , Which of the following is not correct?, , (a) Four spheres are involved in the, formation of tetrahedral void., , (b) The centres of spheres in octahedral, voids are at the apices of a regular, tetrahedron., , (c) If the number of atoms is N the number, of octahedral voids is 2N., , (d) If the number of atoms is N/2, the, number of tetrahedral voids is N., , *(7) Acompound forms hep structure. Number, , of octahedral and tetrahedral voids in 0.5, , of.s) ance is D €, , *(6), , )8.011 10?" 6.02:, , 6.022 x 10", 3:011.x 10, c) LA x 10,2014 x 1078, d).6011 x 10: 10, , , , , , unit cell 495 pm. Radius of Pb atom is, , (a) 205 pm (b) 185 pm, (c) 260 pm (d) 175 pm, (9) In solids the constituent particles may, be _, (a) atoms, (b) ions, , (c) molecules, (d) any one of the above three, (10) A single substance that exists in two or, more forms is called ___, (a) polymorphous __(b) amorphous, (c) isomorphous (d) monomorphous, (11) The ability of crystalline solids to change, physical properties when measured in, different directions is called, (a) anisotropy (b) morphotropy, (c) isotropy (d) polytropy, (12) When the composition of solid changes, with direction then in crystalline, solid arises.