Chemistry: Atom Molecules Arithmetic: Importance and Scope of Chemistry (For CBSE, ICSE, IAS, NET, NRA 2022)

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Importance and Scope of Chemistry

  • Chemistry helps us to understand the composition, structure and changes of matter.
  • In our day today life some of the chemicals are being used as food apart from being an ingredient.
  • Chemical reactions occur the moment we breathe, eat or just sit.
  • Chemicals form an important segment of glass, cement, paper, textile, leather, dye industries.
  • An Atom is defined as the smallest particle of a chemical element that can exist.
  • A Molecule is defined as the group of atoms bonded together that take part in a chemical reaction.

Basic SI Units

  • In 1960, the ‘General Conference of Weights and Measures’ , the international authority on units proposed a new system which was based upon the metric system. This system is called the ‘International System of Units’ which is abbreviated as SI units from its French name,
  • Some of the basic SI units are the Kilogram (Kg) for mass, the second (S) for time, the Ampere (A) for electric current, the Kelvin (K) for temperature, the candela (cd) for luminous intensity.
Table Supporting: Importance_and_Scope_of_Chemistry
Physical QuantityName of SU UnitSymbol for SI Unit
LengthMetrem
MassKilogramkg
TimeSeconds
Electric CurrentAmpereA

Mole Concept

Defining the Mole
  • One mole is defined as the amount of substance of a system which contains as many entities like, atoms, molecules and ions as there are atoms in 12 grams of carbon.
  • A mole of a substance is defined as: The mass of substance containing the same number of fundamental units as there are atoms in exactly 12.000 g of Carbon-12. Fundamental units may be atoms, molecules, or formula units, depending on the substance concerned.

Avogadro Constant

Mole and Avogadro Constant

The Avogadro constant (symbols: L, NA) is the number of particles (usually atoms or molecules) in one mole of a given substance. Its value is equal to . The constant was named after the Italian scientist Amedeo Avogadro.

Atomic and Molecular Masses

Atomic and Molecular Masses
  • An Atomic mass is defined as the mass of a single atom of a chemical element. It is approximately equivalent to the number of protons and neutrons in the atom (the mass number) .
  • Molecular mass is defined as the number equal to the sum of the atomic masses of the atoms in a molecule.

Laws of Chemical Combination

Laws of Chemical Combination
  • This law states that a matter can neither be created nor destroyed. In other words the sum of mass of reacting mixture and the products formed remains constant.

Dalton՚s Atomic Theory

Dalton՚s Atomic Theory
  • The relative number of atoms of each element in a given compound is always the same.
  • During Chemical reactions Atoms are neither created nor destroyed.
  • The atoms of different elements vary in size and mass.
  • In a given compound, the relative number of atoms of each element is always the same.
  • For example, carbon and oxygen form two compounds: carbon monoxide and carbon dioxide. Carbon monoxide contains 1.3321 g of oxygen for each 1.0000 g of carbon, whereas carbon dioxide contains 2.6642 g of oxygen for 1.0000 g of carbon.
  • Atomic theory explains this by saying that carbon dioxide contains twice as many oxygen atoms for a given number of carbon atoms as does carbon monoxide. The deduction of law of multiple proportions from atomic theory was important in convincing chemists of the validity of the theory.
  • The postulates of Dalton՚s Atomic Theory are:
    • Matter consists of indivisible atoms.
    • All the atoms of a given chemical element are identical in mass and in all other properties.
    • Different chemical elements have different kinds of atoms and in particular such atoms have different masses.
    • Atoms are indestructible and retain their identity in chemical reactions.
    • The formation of a compound from its elements occurs through the combination of atoms of unlike elements in small whole number ratio.

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