Key Concept

Understand basic fundamentals
  • Chemistry: a branch of science which  deals with composition , structure and properties of matter.
  • Matter: Anything which occupies space and has mass.The quantity of matter is its mass.
  • Chemical Substance: Any material with a known chemical composition.
  • Classification of Matter:
    • Physical Classification
    • Chemical Classification
  • Physical Classification:
    • Solids : They have a Volume & shape.  Ex.: wood , sugar , gold etc.
    • Liquids: They have a Volume but no shape. Ex.: water , oil , milk etc.
    • Gases : They have no fixed Volume or shape.  Ex.: O2, N2, H2 etc..
  • Chemical Classification:
    • Mixtures: contain more than 1 substance in any proportion.
      • Homogeneous Mixtures : which have uniform composition throughout.  It can not be seen even with a microscope. Ex. sugar , glucose , salt , urea etc.
      • Heterogeneous Mixtures :which do not have uniform composition throughout.  It can be seen with a microscope. Ex.: oil, water , cement, sand , iron , sulphur , rice , wheat , mud etc..
    • Pure substance: Have definite composition.
      • Elements: which contains only one kind of atoms. Ex. Copper, Silver, Gold, oxygen  , nitrogen etc...
      • Compounds: which contains two or more atoms of different elements. Ex.  CO2 , H2O , NH3 , SO2,
 Classification of Matter

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.

Structure of Atoms

Calculation of number of proton:

  1. The protons are positively charged particles present in the nucleus of an atom.
  2. The number of proton in an atom is equal to the atomic number of that element.
  3. Thus, Number of protons=Atomic number (Z)

Calculation of number of electron:

  1. The electrons are negatively charged particles that revolve in the shells around the nucleus.
  2. The number of electron in a neutral atom is equal to the atomic number of that element.
  3. Thus, Number of electrons in a neutral atom=Atomic number (Z)

Calculation of number of neutron:

  1. The neutrons are electrically neutral particles present in the nucleus of an atom.
  2. The mass number is the sum of the number of protons and number of neutrons of the element.
  3. Thus, the number of neutrons can be calculated from the mass number of the element.
  4. Thus, Number of neutrons=Mass number (A) - Atomic number (Z)

Example: Carbon (C) atom:

Atomic number of an element = No of electrons in one neutral atom = 6

The atomic number of Carbon is 6. Thus, Number of protons=Number of electrons=6

∴ The mass number of Carbon = No. of proton + No of neutron   =  6 + 6 = 12

Thus, Number of neutrons= Mass No. - Atomic Number =  12-6=6

Thus, the number of protons, electrons and neutrons in a Carbon atom are 6, 6 and 6 respectively.

Mock Test