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ChemContent | Some Basic Concepts of Chemistry ChemContent 1 Introduction: Chemistry is the science of molecules and their transformations which deals with the study of matter, its composition, the changes that matter undergoes and the relation between changes in composition and changes in energy. Chemistry plays an important role in meeting human needs for food, health care products. Branches of Chemistry: • Organic Chemistry- This branch deals with study of carbon compounds especially hydrocarbons and their derivatives. • Inorganic Chemistry- This branch deals with the study of compounds of all other elements except carbon. It largely concerns itself with the study of minerals found in the Earth's crust. • Physical Chemistry- The explanation of fundamental principles governing various chemical phenomena is the main concern of this branch. It is basically concerned with laws and theories of the different branches of chemistry. • Industrial Chemistry- The chemistry involved in industrial processes is studied under this branch. Analytical Chemistry-This branch deals with the qualitative and quantitative analysis of various substances. • Biochemistry- This branch deals with the chemical changes going on in the bodies of living organisms; plants and animals. • Nuclear Chemistry- Nuclear reactions, such as nuclear fission, nuclear fusion, transmutation processes etc. are studied under this branch. Importance of Chemistry: Chemistry plays a central role in science and is often intertwined with other branches of science. Principles of chemistry are applicable in diverse areas, such as weather patterns, functioning of brain and operation of a computer, production in chemical industries, manufacturing fertilisers, alkalis, acids, salts, dyes, polymers, drugs, soaps, detergents, metals, alloys, etc., including new material. Chemistry contributes in a big way to the national economy. It also plays an important role in meeting human needs for food, healthcare products and other material aimed at improving the quality of life. Matter Matter is any thing that occupies space, has mass, offer resistance and can be perceived of directly by our senses. For example, book, pen, pencil, water, air, all living beings, etc.
ChemContent | Some Basic Concepts of Chemistry ChemContent 2 Element Element is the purest form of matter. It is made up of only one type of atoms, ex.- carbon, iron, copper, oxygen etc. Compound Compound is the substance which is made up of two or more elements combined together in a fixed ratio by their weight e.g., carbon dioxide. Mixture Mixture is the substance which is made up of two or more substances in any ratio. e.g., Sugar + Water, Sodium Chloride + Water, Sand + Water On the basis of composition, mixtures are of following type: ➢ Homogeneous mixture: The mixture which has uniform composition through out e.g., sugar solution. ➢ Heterogeneous mixture: The mixtures which do not have uniform composition through out. e.g. sand in water. Atom Atom is the smallest particle which may or may not exist free but takes part in chemical reaction. Atom word means not to be cut. Ex- H, Na, O etc. International System of Units (S.I.)
ChemContent | Some Basic Concepts of Chemistry ChemContent 3 The international system of units (in French Le Systeme International d' Unité s - abbreviated as SI) was established in 1960 by the 11th general conference on weights and measures. SI system is a modification of metric system and has seven base units pertaining to the seven fundamental scientific quantities. Prefixes in SI system Definition of SI Base Units • Metre: The metre is the length of the path travelled by light in vacuum during a time interval of 1/(299792458) of a second. • Kilogram: The kilogram is the unit of mass; it is equal to the mass of the international prototype of the kilogram. • Second: The second is the duration of 9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom.
ChemContent | Some Basic Concepts of Chemistry ChemContent 4 • Ampere: The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 metre apart in vacuum, would produce between these conductors a force equal to 2 × 10-7 newton per metre of length. • Kelvin: The kelvin, unit of thermodynamic temperature, is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water. • Mole: The mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon-12; its symbol is “mol”. • Candela: The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 × 1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian. Uncertainty in Measurement All scientific measurements involve certain degree of error or uncertainty. Scientific notations, significant figures and dimensional analysis help us in many ways in presenting of data and theoretical calculations. Scientific Notation It is an exponential notation in which any number can be represented in the form N × 10n where n is an exponent having positive or negative values and N can vary between 1 to 10. Thus, 232.508 can be written as 2.32508 × 102 in scientific notation. Precision and Accuracy Precision refers to the closeness of various measurements for the same quantity. However, accuracy is the agreement of a particular value to the true value of the result. Let the true value of a quantity is 3.9 and its measurements taken by two boys are 3.6 and 3.8. Here 3.8 is more accurate as it is closer to the true value. Similarly 3.85 is more precise than 3.9. Significant Figures i. The total number of digits in measuring of any physical quantity with certainty is called significant figures. There are certain rules for determining the number of significant figures. ii. All digits are significant except zero in the beginning of a number. For example, in 285 cm, there are three significant figures. iii. Zeros to the left of the first non-zero digit are not significant if such zeros follow the decimal point. For example, 0.03 has one significant figure. iv. Zeros to the right of the decimal point are significant. For example, 0.200 g has three significant figures. v. Zeros between two non-zero digits are significant. Thus, 2.005 has four significant figures. vi. Counting the numbers of object, for example, 2 balls or 20 eggs, have infinite significant figures as these are exact numbers and can be represented by writing infinite number of zeroes after placing a decimal i.e., 2 = 2.000000 or 20 = 20.000000. Notes: In additions or subtractions, the final result should be reported to the same number of decimal places as that of the term with the least number of decimal places.