Question

Why did Thomson’s results from experimenting with cathode rays cause a big change in scientific thought about atoms

Answer 1

It caused a big change in scientific thought about atoms because from that experiment he discovered one of the atom's sub-particles, which is the negative charged electron.  

Answer 2

Answer is: Tomson concluded that atoms are divisible and that the corpuscles are their building blocks (atoms are made up of smaller particles).

J. J. Thomson discovered the electron in 1897.

His "plum pudding" model (1904) suggested: the electrons are embedded in the positive charge.

With this model, he abandoned his earlier hypothesis (the atom was composed of immaterial vortices).