Table of contents
CHAPTER-1 BASIC DEFINITIONS IN CHEMISTRY
CHAPTER-2 BASIC LAWS OF CHEMISTRY
This book “Basic definitions and Basic laws of chemistry” is an approach for compilation and making a handbook in very simple and easy language to very commonly used terms in chemistry for higher secondary, under-graduate and post graduate students. Many times we are familiar with some terms but a certain times like competitive examinations, interviews, Olympiads it just need a glimpse to all these so as to revise it. This book provides a highlight to almost all basic terms used in chemistry from higher secondary education to post graduation. It tries to cover all basic definitions and basic laws important for interviews, college exams, competitive exams and other such events. This has been designed in simple language and colorful way so as to help students during end-time revision and reducing their quality time to be wasted on searching such basic terms from various sources.
Ms. Hency H. Thacker is currently pursuing Ph.D under the guidance of Dr. Vijay R. Ram from department of chemistry, KSKV Kachchh University, Bhuj (Kachchh). She has qualified IIT-JAM 2016, GSET 2018 and IIT-GATE 2019. She is published 2 review papers and 1 book entitled “Dye removal from aqueous solutions using low cost bioadsorbents derived from agricultural waster: A review”, “Plant mediated synthesis of iron nanoparticles and their applications: A review” and “Biogenic synthesis of metal nanoparticles and their applications” respectively. She has 1 year 6 months of teaching experience at department of chemistry, KSKV Kachchh University, Bhuj(Kachchh).
CHAPTER-1 BASIC DEFINITIONS IN CHEMISTRY
1. Atomic number: Atomic number is defined as number of protons in the nucleus and amount of nuclear charge (Z+). It is alike to the number of electrons in the neutral atom and is denoted by Z.
2. Mass number: Mass number is defined as the total number of nucleons i.e. protons and neutrons in the nucleus.
3. Qualitative analysis: The identification of elements, spieces and/or compounds present in the sample is called qualitative analysis.
4. Quantitative analysis: The determination of absolute or comparative amounts of elements, spieces or compounds present in the sample is called quantitative analysis.
5. Equivalent mass: Equivalent mass is defined as the number of parts of a substance that combines with 1.008 parts by mass with hydrogen, 8 parts by mass of oxygen, 35.5 parts by mass with chlorine.
6. Concentration: Concentration is a general measurement unit stating the amount of solute present in a known amount of solution.
Concentration =amount of solute / amount of solution
7. Normality: Normality (N) is defined as the number of equivalent weights of solute dissolved per litre solution.
Normality (N) = number of equivalent weights of solute/ litres solution
8. Molarity: Molarity (M) is defined as the moles of solute dissolved per litre solution.
Molarity (M) = moles solute / litre solution
9. Molarity: Molarity (M) is defined as the moles of solute dissolved per litre solution.
Molarity (M) = moles solute / litre solution
10. Molality: Molality (m) is defined as the moles of solute dissolved per kilogram solvent.
Molality (m) = moles solute / kg solvent
11. Formality: Formality (F) is defined as the number of formula weights of solute dissolved per litre solution.
Formality (F) = number FWs solute/ litres solution
12. Weight %: Weight % (%w/w) is defined as the grams of solute dissolved per 100 gm solution.
Weight % (%w/w) = gm of solute/ 100 gm solution
13. Volume %: Volume % (% v/v) is defined as the milliliters of solute dissolved per litre solution.
Volume % = mL solute / 100 mL solution
14. Weight to volume %: Weight to volume % is defined as the weight of solute dissolved per 100 ml solution.
Weight to volume % = gm of solute / 100 mL solution
15. Parts per billion: Parts per billion (ppb) is defined as the nanograms of solute dissolved per gram of solution.
Parts per billion (ppb) = gm of solute / 10 gm solution
16. Mole fraction: Mole fraction is the ratio of the number of moles of one component to the total number of moles of solution.
Mole fraction (Χ1) = x1/x1+x2
Where Χ1 is the mole fraction of component 1, x1 and x2 are the number of moles of component 1 and 2 respectively.
17. Oxidation: According to classical concept, oxidation is a reaction which involves the addition of oxygen or any other electronegative element or the removal of hydrogen or any other electropositive element. According to electronic concept, oxidation is a process which involves loss of electrons by an atom or a group of atoms.
18. Reduction: According to classical concept, reduction is a reaction which involves the addition of hydrogen or any other electropositive element or the removal of oxygen or any other electronegative element. According to electronic concept, reduction is a process which involves gain of electrons by an atom or a group of atoms.
19. pH: The pH of a solution may be defined as the negative logarithm of the hydronium ion concentration in moles per litre.
pH = -log[H3O]+
Where [H3O]+ is the concentration of hydronium ions in the terms of moles/litre.
20. Element: The simplest pure form of matter which cannot be decomposed by ordinary chemical means nor it can be formed by the combination of other substances.
21. Loschmidt number: The number of molecules present in 1 ml of a gas at N.T.P is called loschmidt number. Its numeric value is 2.688*10.
22. Empirical formula: The formula which gives the simple whole number ratio of the atoms of various elements present in one molecule of the compound is called empirical formula.
23. Molecular formula: The formula which gives the actual number of atoms of various elements present in one molecule of the compound is called molecular formula.
24. Limiting reagent or limiting reactant: The reactant which is completely consumed when a reaction goes to completion is called the limiting reagent or limiting reactant.
25. Excess reagent: The other reactants present in quantities greater than those needed to react with the quantity of the limiting reagent present would be left unreacted. It is called excess reagent.
26. Basicity of an acid: Basicity of an acid is defined as the number of replaceable hydrogen atoms in one molecule of an acid.
27. Acidity of a base: Acidity of a base is defined as the number of replaceable OH groups in one molecule of a base.
28. Nucleons: Nucleus of an atom consists of proton and neutron and these are collectively known as nucleons.
29. Isotopes: The atoms of the same element having the same atomic number but different mass number are called isotopes.
30. Isobars: The atoms having the same mass number but different atomic numbers are called isobars.
31. Isotones: The atoms having the same number of neutrons but different mass number are called isotones.
32. Isoelectronic species: These are atoms, molecules, or ions having same number of electrons.
33. Isosters: Molecules having the same number of atoms and also same number of electrons.
34. Wavelength of the wave: The distance between two adjacent crests or troughs is called amplitude of the wave.
35. Frequency of the wave: The number of waves which pass through a given point in one second is known as frequency.
36. Velocity of the wave: The distance travelled by the wave in one second is called velocity of the wave.
37. Amplitude of the wave: It is the height of crest or depth of trough of wave and determines intensity or brightness of radiation.
38. Wave number: Wave number is defined as the number of wavelengths per centimeter and is equal to the inverse of wavelength expressed in centimeter.
39. Spectrum: The splitting of light into seven colors and the assemblage of the series of color bands is called a spectrum.
40. Electromagnetic spectrum: The arrangement of different types of electromagnetic radiations in the order of increasing wavelengths is known as electromagnetic spectrum.
41. Atomic spectrum: The spectrum obtained by analyzing the radiations emitted or absorbed by atoms is called atomic spectrum.
42. Emission spectrum: The spectrum obtained by analyzing the radiations emitted from substance is called emission spectrum. It is line spectrum.
43. Absorption spectrum: The spectrum obtained by analyzing the radiations absorbed by the substance from white light is called absorption spectrum.
44. Ionization energy: Ionization energy is the energy required to remove the electron from the outermost orbit of the atom in the gaseous state.
45. Photoelectric effect and photoelectrons: The phenomena of ejection of electrons from the surface of a metal when light of suitable frequency strikes on it is called photoelectric effect and electrons ejected are called photoelectrons.
46. Threshold frequency: The minimum energy of light required to cause emission of electrons from a metal surface is called threshold frequency.
47. Orbit: The circular path of rotation of electrons around the nucleus is called orbit.
48. Orbital: The region around the nucleus of an atom where probability of finding the electrons is maximum is called orbital.
49. Principal quantum number: Principal Quantum number describes the main energy shell or level in which the electrons are present.
50. Azimuthal or angular quantum number: Azimuthal quantum number describes the angular momentum of electrons and gives sub-shell or sublevel in a given principal shell to which the electron belongs.
51. Magnetic quantum number: Magnetic quantum number gives the different orientations of orbital in space.
52. Spin quantum number: Spin quantum number describes the spin of orientation of electrons.
53. Nodes: Nodes are the positions where radial function passes through zero and the probability of finding the electrons at that point is zero.
54. Angular nodes or nodal planes: The planes on which the angular wave function passes through zero are called angular nodes or nodal planes.
55. Atomic radius: Atomic radius is the effective size which means the closest approach to another atom in a given bonding situation.
56. Covalent Radius: It is one half of the distance between the centers of nuclei of two similar atoms held together by a purely covalent single bond.
57. Metallic Radius: It is one half of the distance between two adjacent atoms of a metal in a metallic lattice.
58. Ionic radius: Ionic radius is the effective distance from the nucleus of the ion up to which it has an influence in the ionic bond.
59. Electron gain enthalpy or electron affinity: Electron gain enthalpy is the enthalpy change when an electron is added to the isolated gaseous atom.
60. Electro negativity: Electronegativity is defined as the tendency of an atom to attract the shared pair of electrons towards itself in a molecule.
61. Chemical bond: The attractive force which holds together the constituent particles (atoms, molecules or ions) in a chemical compound is known as chemical bond.
62. Ionic or electrovalent bond: The electrostatic force of attraction which holds the oppositely charged ions together is known as ionic bond or electrovalent bond.
63. Covalent bond: Covalent bond is formed by the mutual sharing of electrons between the combining atoms of the same or different atoms.
64. Coordinate bond: This bond is formed by sharing of electrons between two atoms where both the electrons of the shared pair are contributed by one atom and the other atom merely participates in sharing. The atom which contributes the electrons is called the donor while the other which only shares the electron pair is known as acceptor.
65. Polarization: The distortion of electron cloud of the negative ion by the positive ion is called polarization.
66. Sigma bond: This type of covalent bond is formed by the end to end overlapping of bonding orbitals along the internuclear axis.
67. Pi bond: This type of covalent bond is formed by the sidewise overlap of the half-filled atomic orbitals of bonding atoms.
68. Dipole moment: Dipole moment is defined as the product of the magnitude of charge on the atom and the distance between them.
69. Geometry of molecule: The definite relative arrangement of the bonded atoms around the central atom in a molecule is known as geometry of the molecules.
70. Hybridization: Hybridization is defined as the intermixing of atomic orbitals of slightly different energies so as to redistribute their energies and to form new orbitals of equivalent energies and shapes.
71. Hybrid orbitals: The new orbitals formed as a result of hybridization are called hybrid orbitals.
72. Hydrogen bond: The attractive force which binds the hydrogen atom of one molecule with electronegative atom (F, O , N) of another molecule is known as hydrogen bond.
73. Intermolecular hydrogen bond: Intermolecular hydrogen bond is hydrogen bond formed between two different molecules of the same or different substances.
74. Intramolecular hydrogen bond: Intramolecular hydrogen bond is formed between the hydrogen atom and highly electronegative atom (F , O , N) present in the same molecule.
75. Triple point: The three states of matter can exist together at one particular temperature and pressure. This state is called triple point.
76. Isotherms: The plots of volume vs. pressure or pressure vs. product of pressure and volume are called isotherms.
77. Isobars: The plots of volume vs. temperature at constant pressure are called isobars.
78. Isochores: The plots of pressure vs. temperature at constant volume are called isochores.
79. Most probable velocity: The speed possessed by maximum fraction of molecules of a gas at a particular temperature is called most probable velocity.
80. Average or mean speed: The arithmetic mean of the different speeds of the molecules present is called average or mean speed.
81. Root mean square speed: The square root of the mean of the squares of different speeds of molecules of a gas.
82. Ideal gas: The gases which obey ideal gas equation (PV=nRT) and other gas laws at all temperatures and pressures are called ideal gases. Here P,V,T are the pressure , volume and temperature of the gas respectively, n is the number of moles of the gas and R is Rydberg’s gas constant.
83. Real gas: The gases which do not obey ideal gas equation (PV=nRT) and other gas laws at all temperatures and pressures are called non ideal or real gases.
84. Collision frequency: The total number of collisions taking place in a unit volume per second is called the collision frequency.
85. Mean free path: Mean free path is defined as the average distance travelled by a molecule between two successive collisions.
86. Critical temperature: The temperature above which a gas cannot be liquefied however high the pressure maybe is called critical temperature.
87. Critical pressure: The minimum pressure required to liquefy the gas at the critical temperature is called critical pressure.
88. Critical volume: The volume occupied by one mole of the gas at critical temperature and pressure is called critical volume.
89. Boyle’s temperature: The temperature at which the real gas exhibits ideal behavior for considerable range of pressures is called Boyle’s temperature.
90. Inversion temperature: The temperature at which the gas neither shows heating effect nor show cooling effect is called inversion temperature.
91. Molar heat capacity: The quantity of heat required to raise the temperature of one mole of a gas by 1C is called molar heat capacity.
92. Joule Thomson effect: When a gas under pressure is allowed to expand into a region of constant pressure, there occurs fall in its temperature. This is called Joule Thomson effect.
93. Evaporation: The process of conversion of liquid into its vapor at room temperature is called evaporation.
94. Vapor pressure: The pressure exerted by the vapors in equilibrium with its liquid at a given temperature is called vapor pressure.
95. Boiling point: The temperature at which the vapor pressure of liquid becomes equal to the atmospheric pressure is called its boiling point.
96. Surface tension: Surface tension is defined as the force per unit length acting perpendicular to the tangential line on the surface.
97. Viscosity: The internal resistance to flow in liquids which one layer offers to another layer trying to pass over it is called viscosity.
98. System: A specified area of the universe which is under investigation called the system.
99. Surroundings: The rest of the universe which is not a part of the system is called the surroundings.
100. Isolated system: A system which can neither exchange mass nor energy with the surroundings is called an isolated system.
101. Closed system: A system which can exchange energy but not mass with its Surroundings are called a closed system.
102. Open system: A system which can exchange matter as well as energy with its surroundings is called an open system.
103. State function: A state function is that function whose values whose values depends only on initial and final states of the system and is independent of the path followed.
104. Intensive properties: The properties of the system whose value is independent of the amount of the substance present in the system are called intensive properties.
105. Extensive properties: The properties of the system whose values depend upon the amount of substance present in the system are called extensive properties.
106. Free expansion: Expansion of a gas in vacuum is called free expansion.
107. Process: A process gives the path or operation by which a system changes from one state to another.
108. Isothermal process: A process in which the temperature of the system remains constant is called isothermal process.
109. Adiabatic process: A process in which the system does not exchange heat with the surroundings i.e. no heat enters or leaves the system is called adiabatic process.
110. Isobaric process: A process in which the pressure of the system remains constant is called isobaric process.
111. Isochoric process: A process in which the volume of the system remains constant is called isochoric process.
112. Reversible process: A process in which the direction may be reversed at any stage by merely a small change in the variables like temperature, pressure etc. is called reversible process.
113. Irreversible process: A process in which the direction may not be reversed at any stage by merely a small change in the variables like temperature, pressure etc. is called irreversible process.
114. Internal energy: The sum of different forms of energies stored in atoms or molecules such as translational energy, rotational energy, vibrational energy, electronic energy, energy due to molecular interactions, nuclear energy, etc. is called internal energy.
115. Enthalpy: The sum of the internal energy and product of its pressure and volume is called enthalpy.
H= U+ PV
116. Carnot’s cycle: Carnot’s cycle is an imaginary reversible cycle given by Carnot to demonstrate maximum conversion of heat into work.
117. Heat capacity: The amount of heat required to raise the temperature of the system by one degree is called heat capacity.
118. Specific heat capacity or specific heat: The heat required to raise the temperature of 1 gram of a substance by one degree is called specific heat capacity or specific heat.
119. Heat of fusion: The heat change when 1 mole of a solid substance is converted into its liquid state at their melting point is called heat of fusion.
120. Heat of sublimation: The heat change when 1 mole of a solid substance is directly converted into its gaseous state at a temperature below its melting point is called heat of sublimation.
121. Spontaneous or feasible or probable process: A process which can take place itself under a given set of conditions is said to be spontaneous or feasible or probable process.
122. Driving force: The overall tendency for a process to take place is the resultant of decrease in enthalpy and tendency of a system to acquire a state of maximum randomness is called driving force.
123. Phase transition: The change of matter from one state (solid, liquid or gas) to another is called phase transition.
124. Gibb’s energy: Gibb’s energy of the system is defined as the maximum amount of energy available to the system during a process that can be converted into useful work.
125. Chemical equilibrium: The state at which the concentration of the reactant and products do not change with time is called chemical equilibrium.
126. State of equilibrium: The state in which the measurable properties of the system (such as pressure, density, color or concentration) do not undergo any further noticeable change under given set of conditions is called state of equilibrium.
127. Electrolytes: The substances which conduct electricity in their molten states or in the form of their aqueous solutions are called electrolytes.
128. Strong electrolytes: The substances which ionize completely into ions in aqueous solutions are called strong electrolytes.
129. Weak electrolytes: The substances which ionize to small extent in aqueous solution are called weak electrolytes.
130. Ionic equilibrium: The equilibrium which is established between the unionized molecules and ions in solution of weak electrolytes is called ionic equilibrium.
131. Degree of dissociation or ionization: The fraction of the total number of molecules of electrolytes which ionize into ions is called degree of ionization or degree of dissociation.
132. Arrhenius acids and bases: According to Arrhenius concept, acid is a substance which dissociates in aqueous solution to give hydrogen ions and base is a substance which dissociates in aqueous solution to give hydroxyl ions.
133. Bronsted Lowry acids and bases: According to Bronsted-Lowry concept, an acid is a substance which can donate proton and a base is a substance which can accept a proton.
134. Amphoteric substances: The substances which are capable of donating as well as accepting proton i.e. it can behave as acid as well as base are called amphoteric substances.
135. Lewis acids and Lewis bases: According to Lewis concept of acids and bases ,an acid is a substance which can accept pair of electrons while a base is a substance which can donate pair of electrons.
136. Conjugate acid base pairs: The pairs of acids and bases which are formed from each other by the gain or loss of proton are called conjugate acid – base pairs.
137. Buffer solutions: Buffer solutions are those which resist change in pH on addition of small amount of acids and bases or on dilution of the solution.
138. Buffer capacity: Buffer capacity is defined as the number of moles of acid or base required to add to one litre of a solution to change the pH by unity.
139. Hydrolysis: The process involving the reaction of the anion or cation of the salt with water to produce an acidic or basic solution is called hydrolysis.
140. Solubility product: The solubility product of a salt at a given temperature is the product of the concentrations of its ions in saturated solution with each concentration term raised to the power equal to the number of ions produced on dissociation of one mole of the substance.
141. Common ion effect: The suppression of the degree of dissociation of a weak acids or weak base by addition of strong electrolyte containing a common ion is called common ion effect.
142. Redox reaction: When oxidation and reduction reaction takes place simultaneously, the overall reaction is known as redox reaction.
143. Oxidizing agent: Oxidizing agent is a substance which accepts one or more electrons and causes oxidation of other substances. Oxidizing agent is itself reduced.
144. Reducing agent: Reducing agent is a substance which can give one or more electrons and causes reduction of other substances. Reducing agent is itself oxidized.
145. Electrochemical cells: The devices in which electrical energy is produced from chemical reactions are called electrochemical cells.
146. Anode : The electrode where electrons are released or oxidation occurs is called anode.
147. Cathode : The electrode where electrons are accepted or reduction occurs is
148. Called cathode.
149. Electromotive force or cell potential: The difference between the electrode potentials of two electrodes constituting an electrochemical cell is called electromotive force or cell potential.
150. Standard electrode potential: The electrode potential of a metal electrode as determined with respect to a standard or normal hydrogen electrode is called standard electrode potential.
151. Electrochemical series or activity series: The arrangement of elements in the order of increasing reduction potential values are called electrochemical or activity series.
152. Hard water: Water which does not produce lather with soap solution readily is called hard water.
153. Soft water: Water which produce lather with soap solution readily is called soft water.
154. Temporary hardness of water: Temporary hardness in water is due to the presence of bicarbonates of calcium and magnesium dissolved in it. Temporary hardness is also called carbonate hardness.
155. Permanent hardness: Permanent hardness is due to the presence of chlorides and sulphates of calcium and magnesium dissolved in water.
156. Catenation: The property of forming bonds with the atoms of the same element is called catenation.
157. Functional group: A functional group may be defined as an atom or group of atoms which determines the characteristic properties of a compound.
158. Inductive effect or I effect: The process of displacement of electrons along the chain of carbon atoms due to the presence of a polar covalent bond at one end of the chain is called inductive effect.
159. Electromeric effect: The complete transference of the shared pair of electrons to one of the atom joined by a multiple bond in the presence of an attacking reagent. This is known as electromeric effect.
160. Hyperconjugation effect: When an alkyl group carrying at least one H atom is attached to an unsaturated carbon atom, it releases the electrons of C-H bond towards the multiple bond. This causes conjugation between the ϭ- electrons of a single bond between carbon and hydrogen and π electrons of the multiple bonds. This phenomenon is called hyperconjugation effect or ϭ-π conjugation or no bond resonance.
161. Homolytic fission: In homolytic fission, the cleavage of covalent bond between two atoms takes place in such a way that each atom retains one electron of the shared pair. This results in the formation of free radicals.
162. Heterolytic fission: Heterolytic fission is unsymmetrical fission so that one of the fragments takes both the electrons of the unshared pair leaving none to other. This results in the formation of carbocations and carbanions.
163. Electrophiles: A positively charged or neutral spieces which is deficient of electrons and can accept a pair of electrons from a negatively charged carbon atom is called electrophile.
164. Nucleophiles: A negatively charged or neutral spieces having unshared or lone pair of electrons and can donate a lone pair of electrons to a positively charged carbon atom is called a nucleophile.
165. Isomers and isomerism: The compounds which have the same molecular formula but different physical and chemical properties are called isomers and this property or phenomena is called isomerism.
166. Structural isomerism: Structural isomerism is the type of isomerism in which two isomers differ from one another in the arrangement of the atoms or groups within the molecules having the same molecular formula.
167. Stereoisomerism: Stereoisomerism is the type of isomerism in which two isomers differ from one another in the arrangement of atoms or groups in space having same structural as well as molecular formula.
168. Chain or nuclear isomerism: Chain or nuclear isomerism is the type of isomerism in which the two isomers differ in the chain of carbon atoms.
169. Position isomerism: Position isomerism is the type of isomerism in which the different isomers differ in the position of the characteristic atoms, groups or multiple bond.
170. Functional isomerism: Functional isomerism is the type of isomerism in which the isomers have different functional groups.
171. Tautomerism: Tautomerism is the type of isomerism in which the isomers differ markedly in the arrangement of atoms but exist in dynamic equilibrium with each other.
172. Optically active substances: The substances which can rotate the plane of polarized light are called optically active substances.
173. Racemic mixture: Racemic mixture is an equimolar mixture of the d- and l- forms of an optically active compound. It is represented as dl.
174. Resolution: The process of separation of racemic mixture into d- or l- forms (enantiomers) is called resolution.
175. Geometrical isomers and geometrical isomerism: The compounds which possess the same structural formula but differ in the spatial arrangement of atoms or groups about the double bond are called geometrical isomers and this phenomenon is known as geometrical isomerism.
176. Conformational isomers: The different arrangements of atoms in a molecule that can be converted into one another by rotation around carbon-carbon single bond are called conformational isomers.
177. Cis and trans isomers: The isomers which has similar groups on the same side of the double bond is called cis and when similar groups are on opposite sides, it is known as trans.
178. Chromatography: Chromatography is a modern method discovered by Tswett. It is based upon the principle of distributing the components of a given organic compound between two phases, one of which is stationary phase and the other is mobile phase. The stationary phase is either a solid or a liquid supported over solid and the mobile phase may be liquid or gas.
179. Reforming: Reforming is the process of converting straight chain alkanes and cyclic alkanes into corresponding hydrocarbons under suitable conditions and catalyst. This process is also called aromatization.
180. Octane number: The octane number of a fuel may be defined as the percentage by volume of iso-octane in the mixture of iso-octane and n-heptane which has same anti-knock qualities as the fuel under examination.
181. Cetane number: Cetane number of a diesel is the percentage of cetane in a mixture of cetane (n-hexadecane) and α-methyl naphthalene which has the same ignition quality as the fuel under examination under the same conditions.
182. Anti-knocking compounds: The compounds which are added to the gasoline or petrol tend to improve the octane number and therefore decrease the knocking in the cylinder of the engine are called anti-knocking compounds.
183. Crystalline solid: The substances whose constituents are arranged in a definite orderly arrangement are called crystalline solids.
184. Amorphous or pseudo solid: The substances whose constituents are not arranged in a definite orderly arrangement are called amorphous or pseudo solids.
185. Isotropy and anisotropy: The substances which have different physical properties in different directions are said to exhibit anisotropy. The substances which have same physical properties in all directions are said to exhibit isotropy.
186. Space lattice: The arrangement of points showing how constituent particles(atoms, ions or molecules) of a crystal are arranged at different positions in a three dimensional space is called space lattice.
187. Unit cell: The smallest repeating unit in space lattice which when repeated over and over again gives the crystal of a given substance is called unit cell.
188. Co-ordination number: The number of nearest neighbours with which a given sphere is in contact is called the co-ordination number.