Chapter 1– Basic Concepts in Chemistry

Chapter 1– Basic Concepts in Chemistry

Chapter 1– Basic Concepts in Chemistry – Quick Revision/Short Notes

High Yield Facts:

  • Some important examples [Symbols with Latin or German derivations] Antimony (Sb > Stibium); Silver (Ag > Argentum);Gold (Au > Aurium); Mercury (Hg > Hydragyrum); Lead (Pb > Plumbum);Tungsten (W > Wolfram) etc.
  • Dalton > 1st to use term Atom in his “Atomic theory”.
  • Berzelius > 1st to distinguish amongst atom and molecules.
  • Avogadro > 1st to use term molecule in “Avogadro’s hypothesis”.
  • Atom- is “the smallest particle of an element to take part in chemical reaction” whereas molecule “the smallest particle of’ element/compound having»-independent existence.


  • The concept of element was first introduced by Robert Boyle.
  • A simplest form of substances which can neither be decomposed into nor be composed from simpler substances by ordinary physical and chemical processes is called element.
  • Around 114 elements are known, out of which 92 are natural and rest 22 are artificial.
  • Artificial elements can be synthesized by special kind of nuclear process.
  • About ¼ of natural elements are free in nature and all other elements are found in nature only in combined state. Eg, H2, 02, N2, Au, Pt etc > free existing_Na, Ca, Zn etc > combined state.
  • Four most abundant elements on earth crust: O2>Si>Al>Fe



  • Electropositive in character and exist in solid state (except Hg).
  • Malleable, lustrous and ductile.
  • High melting and boiling point.
  • Good conductor of heat and electricity
  1. Ag, Cu, Au, Fe, Na etc.


  • Electronegative in nature and exist in all three states eg. C-solid, Br2 – liquid, Cl2 -gas.
  • Neither malleable nor ductile.
  • Non-lustrous (except iodine)
  • Low melting and boiling point except diamond


  • Showing the characteristics in between metal and non-metal. Eg. As, C, Sb, Ge, Te etc.
  • Compounds “are formed’ by chemical union of 2 or more elements in fixed proportion by weight.
  • Atomic number = no. of protons.
  • Mass number = no. of nucleons = no. of protons + no. of neutrons.
  • Atomic weight = Average of the product of isotropic mass and relative abundance.
  • If an element has x % of A isotope & y % of B isotope.


Then, At. wt= x % of A + y % of B

(where, A  & B are respective mass numbers of isotopes).

  • For an element zXA,

No. of electrons = no. of protons =Z & No. of neutrons = A – Z.

  • Fractional atomic weight of an element is because of existence of isotopes.
  • Radius of an atom is of the order 10-8cm (10-10m).
  • Radius of an atomic nucleus is of the order1O-12cm (10-14m)
  • This is why, the size of nucleus is said to be negligible when compared» to that of an atom.
[Suggestion box: Note the unit used in order of size]


  • Species having same atomic number (same no. of protons) but different mass number.
  • Isomers have different radioactive properties.
  • Isomers have different no. of neutrons.


  • Species having same no. of neutrons.
  • lsotones have different no. of protons.


  • Species having same no. of nucleons.
  • They have different number of-neutrons (n), different number of proton(P) but

n1 + p1= n2+ p2

  • They have same mass no. but different atomic number.


  • Species having same difference of neutron and proton (n-p).
  • An alpha-decay produces isodiaphere as compared to the parent atom.

Isoelectronic: Atoms or radicals having same number of electrons.

Isoatomic: Molecules having same number of atoms.

  • Isotopes:

Same atomic number but different mass number.

Eg. Hydrogen:

1H1                1H2                     1H3

Proton     Deuterium            Tritium

  • An element has mass 14 and number of neutrons 8 then it is an isotope of carbon.

For more quick revision notes in Chemistry click HERE

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