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Atomic Structure — CHEMISTRY STD 8 — Question

ICSE BoardEnglish MediumSTD 8CHEMISTRYAtomic Structure4 Marks
Question
State the main postulates of $-$ Dalton’s atomic theory. Explain how the modern atomic theory contradicted Dalton’s atomic theory.
✓

Answer

$a.$ Dalton’s Atomic Theory :
The main postulates of theory are :
$1.$ Matter consists of small indivisible particles called $-$ atoms i.e. Atom is the basic unit of matter.
$2.$ Atoms of the same element are $-$ alike in all respects i.e. atoms of hydrogen have same properties like mass, density and atoms of oxygen are alike in all respects.
$3.$ Atoms of different elements are different from each other. i.e. atoms of hydrogen are different from atoms of oxygen.
$4.$ Atom can neither be created nor destroyed.
$5.$ Atoms combine with other atoms in simple whole number ratio forming compounds or molecules.
$b.$ Modern atomic theory contradicted Dalton Atomic Theory as :
$1.$ Atom is no longer indivisible as atom has been divided and has sub$-$atomic particles
$a.$ Protons
$b.$ Neutrons
$c.$ Electrons
$2.$ Atoms of same element may have different properties i.e.
i. e. Isotopes $\ce{^1_1H, ^2_1H, ^3_1H}$
$3.$ Atoms of different elements may have same properties i.e. isobars
$4.$ Atoms combine with other atoms may not be in simple whole number ratio i.e. $($Sugar$)$.
$5.$ Atom can be destroyed and converted into energy.

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