ICSE Class 9 Answered
Dalton’s Atomic Theory
The main postulates of Dalton’s atomic theory are:
· Matter consists of very small and indivisible particles called atoms.
· Atoms can neither be created nor be destroyed.
· The atoms of an elements are alike but they differ from atoms of other elements.
· Atoms of element combine with toms of other element in a simple ratio to form molecules of compound.
· Atoms are smallest part of matter that can take part in chemical reaction.
Dalton’s theory did not propose anything about the charges in an atom as he considered the atom to be indivisible. Therefore, the theory was not able to explain the behaviour and properties of matter.
Element
Element is pure substance that can neither be decomposed into, nor formed from simple substance by ordinary physical or chemical methods.
Element is a substance which is made up of only one type of atoms.
Example: Carbon is an element as it cannot be split up into two or more simpler substances by any ordinary method.
Definition of an Atom
An atom is the smallest particle of an element that exhibits all the properties of that element.
It may or may not exists independently but takes part in every chemical reaction.