As per Ancient philosophy,
Atoms are smallest units of matter that cannot be divided into smaller and smaller components
When we divide matter smaller and smaller components
we reach a stage when no more division is possible
These particles are called atoms.
Maharshi Kanad also proposed a similar philosophy
If we go on dividing padarth (matter) into smaller and smaller component
a stage will come when particles cannot be divided any further
These particles are called parmanu (atoms)
Modern theory was developed by scientists at the end of the 18th century. This theory was based on experiments (and not philosophy)
As per this theory,
There was a difference between elements and compounds
These different elements combined with each other following the laws of chemical combination.
Let's study these in detail