Q1 of 24 Page 166

Modern atomic theory takes up the wave concept, principle of uncertainty and other latest discoveries to give a clear-cut picture about an atom. State the findings of modern atomic theory.

● An atom is the smallest particle which takes part in chemical reaction.


● An atom is considered to be a divisible particle.


● The atoms of the same element may not be similar in all respects.


ex: Isotopes (17Cl35, 17Cl37 )


● The atoms of different elements may be similar in some respects.


ex. Isobars ( 18Ar40 , 20Ca40 )


● The ratio of atoms in a molecule may be fixed and integral but may not be simple. Ex.C12H22O11 is not a simple ratio. (Sucrose)


● The atoms of one element can be changed into the atoms of another element by transmutation.


● The mass of an atom can be converted into energy. This is in accordance with Einstein’s equation E = mc2 where E = energy, m = mass and c = velocity of light


More from this chapter

All 24 →
9

Identify and correct the mistake in each of the following:

i) The molar volume of gas at STP is 22.4 cm3.


ii) 2 x R.M.M. = V.D.


iii) An atom cannot exist independently.


iv) The ratio of atoms in a molecule may be integral or simple or may not be fixed.


v) H2O is a homo atomic molecule.

 10

Give a single term substitute for each of the following:

i) 6.023 x 1023 molecules ii) 22.4 litres of gas at STP


iii) 1/12th part of the mass of one atom of carbon


iv) The half of relative molecular mass


v) Molecular mass / atomic mass

 2

How will you establish the relation between vapour density and molecular mass of a gas by applying Avogadro’s law?

 3

Calculate the number of moles in:

i) 12.046 x 1023 atoms of Copper


ii) 27.95g of Iron


iii) 1.51 x 1023molecules of CO2