Chemistry Definitions PDF

Chemistry Definitions Pure Substances : Pure substances have a definite chemical composition and definite physical and chemical properties. They are homogeneous , i.e. that their composition is uniform throughout the bulk. E.g.: All elements and compounds Atomicity : The number of atoms present in a...

Chemistry Definitions Pure Substances : Pure substances have a definite chemical composition and definite physical and chemical properties. They are homogeneous , i.e. that their composition is uniform throughout the bulk. E.g.: All elements and compounds Atomicity : The number of atoms present in a molecule of an element is called its atomicity. Compound : A compound is a pure substance composed of two or more elements, combined chemically in a definite proportion by mass. Mixtures : Mixtures can be defined as a kind of matter which is formed by mixing twoor more pure substances (elements / compounds) in any proportion, such that they do not undergo any chemical change and retain their individual properties. (Thus, they are impure substances) Homogeneous Mixture : In this type of mixture, the components are uniformly distributed throughout its volume and cannot be seen separately. Heterogeneous Mixture : In this type of mixture, the components are not uniformly distributed throughout its volume and can be seen separately. Fractional Distillation : The process of separating two or more solids based on their solubility in the same solvent is called fractional crystallisation. Sedimentation : The settling down of suspended, heavy, insoluble solid particles in a solid – liquid mixture when left undisturbed is called sedimentation. Decantation : The process of pouring out the clear liquid (supernatant) without disturbing the sediment is called as decantation. Evaporation : Evaporation is the process of converting the liquid into its vapour state either by heating or by exposing it to air. Crystallisation : The process of formation of solid crystals from a hot super-saturated solution by cooling is called crystallisation. Distillation : Distillation is a process of converting a liquid into vapour by heating and the subsequent condensation of the vapour back into the liquid. Centrifugation : Centrifugation is the method of separating suspended solids from liquids where the mixture is homogeneous. This is also called as churning. Fractional Distillation : Fractional Distillation is the process which involves distillation and the collection of fractions of different liquids that are boiling at different temperatures. Miscible Liquids : Liquids which dissolve in each other completely in all proportions are called miscible liquids. Immiscible Liquids : Liquids which do not dissolve in each other are called immiscible liquids. Chromatography : The process of separating different dissolved constituents of a mixture by their absorption on an appropriate material is called chromatography. Diffusion : The spreading out and intermixing of one substance with another due to the motion of the particles in order to get a uniform mixture is called diffusion. Liquefaction : The process by which a gas is changed into a liquid by applying pressure and reducing the temperature is called liquefaction. Atom : An atom is the smallest particle of an element that exhibits all the properties of that element. It may or may not exist independently, but it takes part in every chemical reaction. Atomic number : The number of protons present in the nucleus of an element is called atomic number which is denoted as ‘Z’. Mass number : The sum of the number of protons and the number of neutrons present in the atom of an element is called the mass number of that element, which is denoted as ‘A’. Electronic Configuration : The arrangement of electrons in different shells (orbits) of an atom of an element is called its electronic configuration. Valance Shell : The outermost shell of an atom is known as the valence shell. Valance Electrons : The electrons present in the valance shell of an atom are called as the valence electrons. Isotopes : Isotopes are atoms of the same element with the same atomic number but a different mass number due to the difference in the number of neutrons in their nucleus. Ions : Ions are the charged particles formed due to the loss or gain of one or more electrons by an atom. Radical : A radical of an atom of an element or a group of atoms of different elements that behaves as a single unit with a positive or negative charge on it. Valency : Valency is a combining capacity of the atoms of an element with the atoms of other elements to form molecules. Symbols : A symbol is a short-hand representation of an atom of a specific element. Each chemical element has its own unique symbol. Basic Radicals : These radicals have a positive charge and are also called as cations. Acid Radicals : These radicals have negative charge and are also called as anions. Molecular Formula : A molecular formula of a compound is the symbolic representation of its molecules. It shows the number of atoms present in it and these atoms combine in whole numbers to form a molecule. Chemical Equations : A chemical equation is the symbolic representation of a chemical reaction using symbols and formulae of the substances involved in the reaction. Reactants : The substances that are used as the starting material and which react with one another are called reactants. Product : The substances which are formed as a result of the reaction are called products. Law of conservation of mass : The law of conservation of mass states that matter can neither be created nor can it be destroyed, it can only be transformed from one form to another. Balanced Chemical Equation : A balanced chemical equation is the one in which the number of atoms of each element on the reactant side is equal to the number of atoms of that element on the product side. Catalyst : A catalyst is a substance which increases the rate of a reaction. Promoter : A promoter is a substance which increases the efficiency of the catalyst. Chemical Reaction : Any chemical change in matter which involves transformation into one or more substances with entirely different properties is called a chemical reaction. Chemical Bond : A chemical bond is an attractive force that holds the atoms or ions of a molecule together. Effervescence : The formation of gas bubbles in a liquid during a chemical reaction is called effervescence. Combination Reaction : A reaction in which two or more substances combine to form a single substance is called a combination reaction / synthesis reaction. Decomposition Reaction : A reaction in which a compound breaks up on heating into two or more simpler substances is called decomposition reaction. Displacement Reaction : A reaction in which a more active element displaces a less active element from compound is called a displacement reaction. Double Displacement Reactions : A chemical reaction in which two compounds in their aqueous state exchange their ions or radicals or ions to form new compounds is called a double displacement reaction or a double decomposition reaction. Precipitation Reaction : A chemical reaction in which two compounds in their aqueous solution state react to form an insoluble solid (precipitate) as one of the products is called as a precipitation reaction. Neutralization Reaction : A chemical reaction in which a base or an alkali reacts with an acid to produce salt and water only is known as a neutralization reaction. Precipitate : A precipitate is an insoluble solid formed when two compounds in their aqueous solution state react chemically with each other. Acids : Acids are the substances which when dissolved in water produce hydrogen ions as the only positive ions in their solutions. Indicators : These are organic compounds which show characteristic colours in acidic and basic solutions. Metal Reactivity Series : A list in which the metals are arranged in a decreasing order of their chemical reactivity is called the metal reactivity series. Exothermic Reactions : A chemical reaction in which heat is given out as a form of energy is called an exothermic reaction, and it causes a rise in temperature. Endothermic Reaction : A chemical reaction in which heat is absorbed is called an endothermic reaction, and it causes a fall in temperature.