Some Basic Concepts of Chemistry

Anything that exhibits inertia is called matter. The quantity of matter is its mass.

Classification of Matter:-
Based on chemical composition of various substances.

âž–It is the simplest form of the matter.
âž–Smallest unit of an element is known as atom.
âž–Total number of the known elements is 118 out of which 98 elements occur naturally and 20 are formed by artificial transmutation.
âž–Examples: Na, K, Mg. Al, Si, P, C, F, Br etc.

âž–It is a non-elemental pure compound.
âž–Formed by chemical combination of two or more atoms of different elements in a fixed ratio.
âž–Examples: H2O, CO2, C6H12O6 etc.

âž–Formed by physical combination of two or more pure substances in any ratio.
âž–Chemical identity of the pure components remains maintained in mixtures.
âž–Homogeneous mixtures are those whose composition for each part remains constant.
âž–Example, Aqueous and gaseous solution.
âž–Heterogeneous mixtures are those whose composition may vary for each and every part.
âž–Example, Soil and concrete mixtures.

🧩Dalton’s Atomic Theory:
âž–Every matter consists of indivisible atoms.
âž–Atoms can neither be created nor destroyed.
âž–Atoms of a given element are identical in properties
âž– Atoms of different elements differ in properties.
âž–Atoms of different elements combine in a fixed ratio to form molecule of a compound.

🧩Precision and Accuracy:
âž–Precision: Closeness of outcomes of different measurements taken for the same quantity.
âž–Accuracy: Agreement of experimental value to the true value

🧩Laws of Chemical Combination:
âž–Law of conservation of mass:
“For any chemical change total mass of active reactants are always equal to the mass of the product formed”

âž–Law of constant proportions:
“A chemical compound always contains same elements in definite proportion by mass and it does not depend on the source of compound”.

âž–Law of multiple proportions:
“When two elements combine to form two or more than two different compounds then the different masses of one element B which combine with fixed mass of the other element bear a simple ratio to one another”

âž–Law of reciprocal proportion:
“ If two elements B and C react with the same mass of a third element (A), the ratio in which they do so will be the same or simple multiple if B and C reacts with each other”.

➖Gay Lussac’s law of combining volumes:
“At given temperature and pressure the volumes of all gaseous reactants and products bear a simple whole number ratio to each other”.

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