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LMR-3 DEFINITIONS / TERMS Atomic Radius / Atomic size - The distance between the centre of the nucleus to the outermost shell is called atomic radius. Ionization potential - The amount of energy required to remove a loosely bound electron from the outermost shell of an isolated gaseous atom. Electron affinity - The amount of energy released when an atom in the gaseous state accepts an electron to form an anion. Electronegativity - The tendency of an atom to attract electrons towards itself when combined in a compound. Oxidation : (i) Loss of hydrogen (ii) Gain of oxygen Reduction : (i) Gain of hydrogen (ii) loss of oxygen (iii) Loss of electron/s (iii) Gain of electron/s Electrovalent bond A chemical bond formed between the atoms of two elements in which one loses electron (metal) and the other gains electron. Electrovalency- The number of electrons donated or accepted by the valence shell of an atom of an element to complete its octet or duplet state is known as electrovalency. Covalent bond- The chemical bond formed by mutual sharing of electrons by the atoms of non-metallic elements is called covalent bond. Covalency- The number of electron pairs, which an atom shares with other atom or atoms to achieve stable electronic configuration, is called Covalency. Lone pair of electrons- the electrons, which are not shared with any other atom in the formation of the bond, are called lone pair of electrons. Lone pair effect- Oxygen is more electronegative than hydrogen, therefore it pulls the electrons towards itself and hence becomes slightly negatively charged, while hydrogen gets slightly positive charge. Co-ordinate covalent bond- It is a bond formed between the atom of a polar covalent molecule with lone pair of the electrons and an ion which accepts the lone pair of electrons. Acids - Acids are defined as compounds which when dissolved in water produce hydronium ions(H3O+) as the only positive ions. Organic acids - These acids are derived from plants. Mineral acids - These acids are usually obtained from minerals. Oxyacids - Acids containing hydrogen, oxygen and some other element. Hydracids - Acids containing hydrogen and a nonmetallic element, but not oxygen. Strong acid - It ionizes completely in aqueous solution producing a high concentration of hydronium ion. Weak acid - It dissociates only partially in aqueous solution producing a low concentration of hydronium ion. Concentrated acid - An acid having relatively high percentage of acid in its aqueous solution. Dilute acid - An acid having relatively low percentage of acid in its aqueous solution. Basicity of an acid - The basicity of an acid is defined as the number of hydrogen/hydronium ions that can be produced by the ionization of one molecule of that acid in aqueous solution. Monobasic acid - It ionizes in aqueous solution to produce one hydrogen ion per molecule of acid. Dibasic acid - It ionizes in aqueous solution to produce two hydrogen ion per molecule of acid. Tribasic acid - It ionizes in aqueous solution to produce three hydrogen ion per molecule of acid. Base - A base is a compound which reacts with with hydronium ions of an acid to give salt and water only. Alkali - An alkali is a compound which when dissolved in water yields hydroxyl ions(OH-) as the only negative ion. Strong alkali - It ionizes completely in aqueous solution producing a high concentration of hydroxyl ion. Weak alkali - It dissociates only partially in aqueous solution producing a low concentration of hydroxyl ion. Acidity of base - The acidity of a base is defined as the number of hydroxyl ions that can be produced by the dissociation of one molecule of that base in aqueous solution. Monoacidic base - It dissociates in aqueous solution to produce one hydroxyl ion per molecule of base. Diacidic base - It dissociates in aqueous solution to produce two hydroxyl ions per molecule of base. Triacidic base - It dissociates in aqueous solution to produce three hydroxyl ions per molecule of base. Indicators - are weak organic compounds which change colour depending on the pH of the solution. pH value of a solution - The pH value represents the strength of acids and alkalis expressed in terms of hydrogen ion concentration[H+] pH - is defined as the negetive logarithm to the base 10 of hydrogen ion [H +] concentration expressed in moles per litre. pH scale- It is a scale showing the relative strength of acids and bases. Universal indicators- universal indicators are mixtures of organic dyes or mixed indicators.eg.pH paper, pH solution. Universal indicators are used to determine the strength of acids or bases, as it gives different colours with different values of pH solutions. Neutralization - The process in which [H+] ions of an acid react completely or combine with [OH-] ions of base to give salt and water only. Salt - A salt is a compound formed by partial or complete replacement of the replaceable hydrogen ion of an acid by a metallic ion or an ammonium ion. Ionic definition- A salt is an ionic compound, which dissociates in water to yield a positive ion other than hydrogen ion[H+] and a negative ion other than hydroxyl ion[OH-]. NORMAL SALT - They are formed by complete replacement of replaceable hydrogen ion of an acid by a metallic or an ammonium ion. Normal salt does not contain any replaceable hydrogen atom in its molecule. Hence it does not show the properties of an acid in solution. ACID SALT - They are formed by partial replacement of the replaceable hydrogen ion of an acid by a metallic or an ammonium ion. It shows all the properties of an acid as it contains replaceable hydrogen atom in its molecule. BASIC SALT - It is formed by partial replacement of the hydroxyl radicals of a diacidic or triacidic base with an acid radical. Hydrolysis - The phenomenon due to which a salt formed by a weak acid and a strong base, or by a strong acid and a weak base, reacts with water to give an acidic or alkaline (or neutral) solution, is known as hydrolysis. Water of crystallization - The amount of water molecules which enter into loose chemical combination with a molecule of salt on crystallization from its aqueous solution is called water of crystallization. Such salts are called hydrated salts. Efflorescence - Crystalline hydrated salts which on exposure to the atmosphere lose their water of crystallization wholly or partly and change into powder.This phenomenon is called efflorescence and the salts efflorescent. Deliquesc ence - Water soluble salts which on exposure to the atmosphere, dissolve in the same and change into a liquid. This phenomenon is called deliquescence and salts deliquescent. Hygroscopic substances - Certain substances absorb moisture from the atmosphere without dissolving in it. Such substances are called hygroscopic substances. They absorb moisture from other substances hence are used as desiccating agents or drying agents. Dehydrating agent - They remove chemically combined elements of water from a compound. Eg.conc. H2SO4 Electrolysis: Electrolysis is the decomposition of a chemical compound (eletrolyte) in the aqueous or fused (molten) state by the passage of electric current resulting in the discharge of ions as neutral atoms at the respective electrode. Electrolyte: It is a compound which in aqueous or in molten state allows electric current to pass through it, which results into its decomposition. Electrode: Electrodes are metal plates or wires immersed in the electrolyte through which the current enter and leave the electrolytic cell. Anode: The electrode connected to the positive terminal of the battery is called anode. The current enters the electrolyte through the anode. They lose electrons and are oxidized. Anion (-ve ions) migrates to anode and gets oxidized to form neutral atoms. Cathode: The electrode connected to the negative terminal of the battery is called cathode. The current leaves the electrolyte through the cathode. They gain electrons and are reduced. Cation (+ve ions) migrates to cathode and gets reduced to form neutral atoms. Electrolytic cell: The vessel in which electrolysis is carried out is called electrolytic cell. It converts electrical energy into chemical energy. Dissociation - The process due to which an ionic compound in the fused or molten state or in aqueous solution dissociates into ions by passage of electric current is called Electrolytic dissociation. Ionization - The process by which polar covalent compounds form ions in water is called ionization. Depending on the ease with which the metals lose their electrons and form ions they are arranged in a series known as Electrochemical series. Inert electrode- Iron , graphite , platinum do not take part in the electrolytic reaction. Hence their discharge will depend on position in the electrochemical series and the concentration of the ions. Active or Attackable electrode- Copper , nickel , silver take part in the electrolytic reaction. If an active electrode is used then the anions migrate to the anode but are not discharged. Instead the active electrode (Cu,Ag,Ni ) itself loses electrons and form ions(Cu2+,Ag1+,Ni2+) Electroplating is the electrolytic process of decomposition of a superior metal ( gold, silver, nickel) on the surface of another metallic article (iron, copper, brass). Electrorefining- It is a process by which metals containing impurities are purified electrolytically to give pure metal. Electrometallurgy- It is the extraction of metals from their ores by the process of electrolysis. Metals, which are higher in the electrochemical series, are extracted by this method. Metallurgy- The large scale processes involved in the extraction of pure metals from their respective ores is called metallurgy. Minerals- The compounds of various metals found in the nature along with earthly impurities are called minerals. Ore- The naturally occurring minerals from which metals can be extracted easily and profitably are called ores. Matrix- The earthly impurities like silica(SiO2) , mud etc. associated with the ore is called matrix or gangue. Pulverisation- The process of crushing the ore into a fine powder is called pulverization. Roasting - It is the process of heating the concentrated ore in the presence of excess air. Calcination - It is the process of heating the concentrated ore in the absence of air at a temperature not sufficient to melt the ore. Rusting - is the slow oxidation of iron by oxygen of the air in the presence of water vapour(moisture). Alloys- is a substance prepared by adding other metals to a base metal so as to obtain certain desirable properties. Amalgam- is an alloy in which the base metal is mercury.e.g.Na/Hg amalgam Constant boiling mixture- On boiling the vapours of both acid and water evolve out in the same proportion as in the liquid. Gay Lussac s Law or Law of combining volume of gases - When gases react they do so in volumes which bears a simple whole number ratio to one another and to the volume of the products, if gaseous, provided the temperature and the pressure of the reacting gases and their products remain constant. Avogadro s Law - Under the similar conditions of temperature and pressure equal volumes of all gases contain the same number of molecules. Avogadro s number- The number of atoms present in 12grams f Carbon 6C12 . Mole- It is the amount of substance which contains the same number of units as the number of atoms in 12.00 grams of Carbon 6C12 Molar volume- It is the volume occupied by 1gram molecular weight of a gas at s.t.p. Relative atomic mass(atomic weight)- The relative atomic mass of an element is the number of times one atom of an element is heavier than 1/12 the mass of an atom of Carbon 6C12. Relative molecular mass(atomic weight)- The relative molecular mass of an element or compound is the number of times one molecule of an element is heavier than 1/12 the mass of an atom of Carbon 6C12. Atomicity- It is the number of atoms present in one molecule of that element. Vapour density- It is the ratio of the mass of a certain volume of gas or vapour to the mass of the same volume of hydrogen (all volumes are measured under the same conditions of temperature and pressure) Empirical formula- It is the formula of a compound which shows the simplest whole number ratio between the atoms of the elements in the compound. Molecular formula- It is the chemical formula which represents the actual number of atoms of each element present in a molecule of the compound. Catenation- It is the tendency of an element to form chains by the atoms of the same element. Functional group - An atom or a group of atoms or some structural features, which is responsible for the characteristic property of an organic compound, is known as Functional group. Isomerism - Organic compounds which have the same molecular formula but different structural formula or molecular arrangement are known as isomers and the phenomenon is known as Isomerism. Esterification: The condensation reaction of a carboxylic acid with alcohol is called esterification. The product so formed is called ester.
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