Some Basic Concepts of Chemistry

Some Basic Concepts of Chemistry

Matter:

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

Classification of Matter:-

Based on chemical composition of various substances.

📍Elements:

➖It is the simplest form of the matter. 

➖Smallest unit of an element is known as atom.

➖Total number of the known elements is 118 out of which 98 elements occur naturally and 20 are formed by artificial transmutation.

➖Examples: Na, K, Mg. Al, Si, P, C, F, Br etc.

📍Compound:

➖It is a non-elemental pure compound.

➖Formed by chemical combination of two or more atoms of different elements in a fixed ratio.

➖Examples: H2O, CO2, C6H12O6 etc.

📍Mixture:

➖Formed by physical combination of two or more pure substances in any ratio.

➖Chemical identity of the pure components remains maintained in mixtures.

➖Homogeneous mixtures are those whose composition for each part remains constant.

➖Example, Aqueous and gaseous solution.

➖Heterogeneous mixtures are those whose composition may vary for each and every part.

➖Example, Soil and concrete mixtures.

🧩Dalton’s Atomic Theory:

➖Every matter consists of indivisible atoms.

➖Atoms can neither be created nor destroyed.

➖Atoms of a given element are identical in properties

➖ Atoms of different elements differ in properties.

➖Atoms of different elements combine in a fixed ratio to form molecule of a compound.

🧩Precision and Accuracy: 

➖Precision: Closeness of outcomes of different measurements taken for the same quantity. 

➖Accuracy: Agreement of experimental value to the true value 

🧩Laws of Chemical Combination:

➖Law of conservation of mass: 

“For any chemical change total mass of active reactants are always equal to the mass of the product formed”

➖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”.

➖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” 

➖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”.