MODERN ATOMIC THEORY


(I) Atoms are composed of still smaller particles which are called electrons, protons and neutrons.
(II) Atoms of the same elements may not be similar in all respect.
(III) Atoms of the different elements may have the same atomic masses.
(IV) Atoms of the different elements may not combine in simple ratio.
(V) Atoms of one elements can be changed into atoms of other elements.

ATOMIC MASS

       The atomic mass of an element is the average relating mass of an atom of the element as compared to the mass of c-twelve atoms taken as twelve unit.

             1 any = 1.66056 × 10(power of -24) g

Atomic mass= mass of atom of the element/mass of 1/12 atoms of the carbon



GRAM ATOMIC MASS

       It can be defined as, the mass of one mole of atom of a particular elements.
Eg:- The atomic mass of oxygen is 16 amu.

Therefore,one gram of oxygen is equal to gram atomic mass of oxygen.

Number of gram atom=mass in gram/gram atomic mass.


MOLECULAR MASS

✓ Molecules are the smallest particles of matter which can have independent existence.

✓Molecular mass is the average relative mass of a molecules of an element or a chemical compounds as compared to the mass of a carbon atom taken as 2F atom mass unit(amu).

e.g. The molecular mass of H2SO4 = 
                      2× atomic mass of H2 + 1×atomic mass of S+ atomic mass of O2.

  = 2×1+1×32+4×16
  =2+32+64
  =98 amu

Gram moles= mass in gram/gram molecular mass

FORMULA MASS

The formula of a molecule is the sum of the atomic mass of the atoms in the empirical formula of the compound.

NaCl
23u + 35.5u = 58.5u


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