DALTON’S ATOMIC THEORY
1)Matter
is made up of extremely small particles called atoms.
2)An
atom is indivisible i.e. it cannot be further subdivided.
3)Atoms
of the same element are identical in all respects.
4)
Atoms of the different elements differ in chemical properties and masses.
5)Atoms
of same or different elements combine to form compound atoms.
6)Atoms
always combine in a simple whole number ratio.
7)Atom
is the smallest particle that takes part in a chemical reaction.
8)Atoms
can neither be created nor destroyed during a chemical reaction.
9)
Chemical reactions involve combination, separation or rearrangement of atoms.
DRAWBACKS OF DALTON’S ATOMIC THEORY
1)It
could not explain the structure of atom.
2)
It could not explain the concept of isotopes and isobars.
3)
It could not explain how atoms of the different elements are different.
4)
It could not explain law of gaseous volumes.
5)
It could not explain Berzelius hypothesis.
6)
It failed to explain the cause of chemical combinations.
7) It failed to distinguish between ultimate particles of an element and a compound.
8) It failed to explain the nature of binding forces between atoms in a molecule.
MODERN ATOMIC THEORY
1)Atom has a complex structure and is divisible into electrons,protons,and neutrons.
2)Atoms of the same element may have different atomic masses. Such atoms are called isotopes. E.g. Hydrogen element has three isotopes:
3) Atoms of the different elements may have same atomic mass. Such atoms are referred to as isobars. E.g. Atoms of argon, potassium and calcium have same atomic mass.
4) Atom is the smallest particle that takes part in a chemical reaction.
5) The ratio in which different atoms combine may not always be simple. E.g. in sugar molecule C12H22O11,the ratio of C,H and O atoms is 12:22:11,which is not simple.
6) Atom is destructible and can be disintegrated by carrying out nuclear reactions.
7) Atom of an element can be converted into another through nuclear reactions.
8) In nuclear reactions mass is converted into energy according to Einstein equation E =mc2.
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