Explanation:
The first atomic model was the one proposed by Jhon Dalton, according to which it is postulated that:
"Matter is made up of indivisible, indestructible and extremely small particles called atoms."
That is, the atom is a solid and indivisible mass.
However, at the end of 19th century the physicist J.J. Thomson began experimenting with cathode ray tubes and found out that atoms contain small subatomic particles with a negative charge (later called electrons).
This means the atom was not indivisible as Dalton proposed. So, Thomson developed in 1904 a new atomic model that was called the raisin pudding atomic model.
Therefore:
IS INDIVISIBLE
Previously it was thought that atoms were indivisible, but his experiment exposed electrons to the world, disproving such a theory.
