What is Atomic Structure ?
- Since ancient times man has been inquisitive about the change of form of matter, for example when salt is added to water it becomes invisible but its taste is there in the water. On being burnt coal converts into ash. Matter can be grounded to form fine powder. The invisibility and divisibility of matter was well known to the Greek and Bhartiya philosophers, way back before Christ.
- It was way back in 6th BC, Maharshi Kanad, the Bhartiya philosopher, had said, “Matter can be divided into small particles but the utlimate minutest particle will remain indivisible.” Kanad named it ‘Parmanu’. Another Bhartiya Philosopher Kaccayana stated that these ‘particles’ are present in combined form which give different forms to matter. At about the same time, Greek philosophers Democratic and Leucippus called these indivisible particles as atoms which means ‘cannot be cut’ or ‘indivisible’ in other words which cannot be divided further. All these views were based on philosophy and did not have a practical basis. In 1808, scientist John Dalton gave the ‘Atomic Theory’ on the basis of chemical combination, conservation of matter and laws of definite proportions.
The main points of the theory are as under :
- All the matter is composed of small particles called ‘atoms’.
- Atoms are indivisible particles which can neither be destroyed nor can be created.
- All the atoms of an element are similar.
- Atoms of different elements have different properties.
- The atoms of different elements combine with each other in whole number proportions to form the molecule of compounds.
- Chemical change is basically the combina tion, dissoc i a tion and reconfiguration of atoms.
By the end of nineteenth century, series of different experiments, made it clear that some small particles are present in atoms which are known as sub atomic particles.
Atomic Structure Important Points :-
- The basic particles of atom are electron, proton and neutron.
- The negatively charged particles in the atom are electrons.
- The numeric value of the charge on electron and proton is the same but their sign is opposite.
- James Chadwick discovered neutrons.
- There are 6.022×1023 particles in one mole. This is known as the Avogadro number.
- The NTP volume of 1 mole of a gas is 22.4 litres.
- The formula to determine the maximum number of electrons in a shell is 2n2 .
- When the atomic number is the same but mass number is different they are known as Isotopes.
- Isobars are elements having different atomic number and the same mass number.
- There are three isotopes of hydrogen, Protium, Deutirium and Tritium.
Atomic Structure Important Questions-Answers
1. The Plum Pudding Model of atom was given by:
(a) Neil Bohr
(b) Thomson
(c) Ernest Rutherford
(d) Goldstein
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2. The discoverer of neutron was :
(a) C.V. Raman
(b) Rutherford
(c) J.J. Thomson
(d) James Chadwick
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3. The size of atom is :
(a) 10-6 cm
(b) 10-15 cm
(c) 10-2 cm
(d) 10-8 cm
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4. The number of neutrons in the Deutirium Isotope of hydrogen is /are :
(a) one
(b) Two
(c) Three
(d) Not even one
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