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Language of Chemistry


The universe is composed of matter and energy. Matter and energy are interconvertible to each other. Chemistry is the branch of science that deals with the properties, composition, and structure of elements and compounds, how they can change, and the energy that is released or absorbed when they change.


  • Pure substance which can neither be decompose into nor built from simpler substance by any kind of physical or chemical methods.
  • Eg: Hydrogen, Oxygen, Chlorine, etc.


  • The smallest particle of element which can take part in chemical change.
  • It may or may not be capable of independent existence.


  • A substance produced by union of two or more elements in definite proportion.
  • It can be decomposed into two or more simple substance.
  • Eg: Water: H2O, Ammonia: NH3, Methane: CH4,etc


  • Smallest unit(particle) of any kind of substance, element or compound which can exist independently and can possess all properties of substance.
  • Eg: , , , etc.
  • Homogeneous Molecule: Formed by the combination of similar kind of atom. Eg: O2,O3,S8,etc
  • Heterogeneous Molecule: Formed by the combination of different kind of the atoms of different elements. Eg: CH4,PCl5,etc


  • Developed by Alchemists
  • Simply a representation of element.
  • Eg: H for Hydrogen, O for Oxygen
  • Few are named with their Latin name. Eg: Au for Gold(Aurum), Ag for Silver(Argentum)
  • Few are named in honor of scientists. Eg: Einstenium(Es) from Albert Einstein
  • Few from name of planets. Eg: Uranium(U) from Uranus
  • Few from Country names. Eg: Americium (Am) from America
  • Many are symbolized from first letters of element. Eg: Sulphur(S), Aluminum(Al)


  • It is the combining capacity with other elements.
  • Measured by number of hydrogen or chlorine atoms which combine with or displace by one atom of element.
  • Eg: Valency of Chlorine:1, Oxygen:2, Nitrogen:3 and Carbon:4
  • Valency of Ag in AgCl is 1, Au is 3 in AuCl3.
  • To make it clear, let us take 'A' and 'B' be two hypothetical elements. A combines with hydrogen to form H2A and B combine with A to form BA3. Find the Valency of B


In H2A, A combine with 2 hydrogen so, valency of A=2

In BA3, B combine with 3 A atom so, valency of B=(3*2)=6

  • Some metals show more than one valency.
  • Metal ends with "Ous" has lower valency.
  • Metal end with "ic" has higher valency.

For Iron:

  1. Ferrous has valency 2. Eg: Ferrous Chloride(FeCl2)
  2. Ferric has valency 3. Eg: Ferric Chloride(FeCl3)


  • Atom or group of atom having positive or negative charge and behave as single unit in chemical change.
  • Eg: Acidic radical: Cl- , SO4- , NO3-
  • Eg: Basic radical: Na+ , Ca++ , NH4+

Monovalent Radicals:

  1. Cyanate (CNS-)
  2. Nitrate(NO3-)
  3. Nitrite(NO2-) [IOE-2077]
  4. Permanganate (MnO4-)
  5. Hypochlorite (ClO-)
  6. Formate(HCOO-)
  7. Acetate(CH3COO-) [IOE]
  8. Perchlorate(ClO4-)
  9. Chlorate(ClO3-)
  10. Chlorite(ClO2- )

Divalent Radicals:

  1. Oxalate(C2O4--) [IOE]
  2. Sulphite(SO3--)
  3. Sulphate(SO4--)
  4. Chromate(CrO4--)
  5. Zincate(ZnO2--)
  6. Manganate(MnO4--)

Trivalent Radicals:

  1. Ferricyanide [Fe(CN)6]-3 [IOE]
  2. Aluminate (AlO3-3)

Some Important Common Names:

  1. Tear gas= CCl3NO2
  2. Vinegar= CH3COOH
  3. Laughing Gas= N2O
  4. Hypo= Na2S2O3.5H2O
  5. Aqua fortis= HNO3
  6. Aqua regia= Conc.HNO3 + 3Conc. HCl
  7. Potassium ferrocyanide= K4[Fe(CN)6]
  8. Potassium ferricyanide = K3[Fe(CN)6]
  9. Oil of Vitriol= H2SO4
  10. Green Vitriol= FeSO4.7H2O
  11. White Vitriol= ZnSO4.7H2O
  12. Epsom Salt= MgSO4.7H2O
  13. Gypsum= CaSO4.2H2O
  14. Antacid= Mg(OH)2.Al(OH)3
  15. Milk of Lime= Ca(OH)2

Points to remember.

  • Atomic number = No. of protons
  • Mass number = No. of protons + no. of neutrons + no. of electrons
  • Atomic weight = Average of product ofisotopic masses and their abundances
  • Fractional atomic weight is due to presence of isotopes.

Compounds and mixture

  • A compound is composed of elements which are chemically combined in definite proportions by weight.
  • A mixture is composed of two or more compounds, each of which retains its own properties.
  • A compound is always homogeneous while a mixture can be separated by physical or chemical methods into its components
  • Filtration: used for the separation of insoluble solid present in a liquid eg: BaSO4 present in aqueous solution, AgCI present in aqueous solution etc.
  • Sublimation: used for the separation of a mixture of two solids. eg: NH;Cl+NaCI, camphor + NaCI, I2 + sand etc.
  • Distillation: used for the separation of a liquid from a solution with solubleimpurities. eg: pure and sea water, alcohol and ether.
  • Fractional distillation: used for the separation of the two miscible liquids. This is based on the difference of their boiling points. eg: a mixture of benzene and toluene etc.
  • Steam distillation: used for the separation of water insoluble liquid from a mixture of two liquids by heating with steam. eg: nitrobenzene, aniline, lemon, oil etc.
  • Crystallization: used for the separation of a dissolved crystalline solid substance from a solution. eg: CuSO; crystals from its aqueous solution.
  • Atmolysis: used for the separation of the mixture of gases or vapours. The method is based on the difference of their diffusion from porous substance. eg: H2 and O2, CH4 +O2, U235 in the form of their hexafluoride.

Iso species

  • Isomers: Species having same atomic number (same number of protons) but different mass number are called isomers.$\\$ Isomers have different radioactive properties as of different number of neutrons.$\\$
  • Isotones: Species having same number of neutrons are called isotones.Isotones have different number of protons.$\\$
  • Isobars: Species having same number of nucleons are called isobars.$\\$ They have different number of neutrons , different number of protons (p) but .$\\$ They have same mass number but different atomic number.
  • Isodiaphers:Species having same difference of neutron & proton (n-p) are called isodiaphers.$\\$ An -decay produces isodaipher as compared to the parent atom.
  • Isoelectronic: Atoms or radicals having same number of electrons are called isoelectronics
  • Isoatomic: Molecules having same number of atoms are called isoatomic.$\\$ [Isosters = Isoelectronic + Isoatomic]
  • Isotopes: Elements having same atomic number but different mass number are called isotopes.$\\$ Eg. Hydrogen has three isotopes namely: $_{1}H^{2}$ $_{1}H^{3}$$\\$Proton Deuterium Tritium $\\$An element has mass number 14 and number of neutron 8; then it will be an isotope of carbon.
  • Isolobel: Atoms with same geometry and hybridization are called isobels$\\$ e.g. SO and SnCl are isobels.
  • Isomorphs: Molecules with same number of atoms bonded in similar fashion are called isomorphs$\\$. Eg: etc.