Question

If atoms are made up of smaller parts such as electrons, why are atoms considered the smallest particles of and element

Answer 1

The element has a smallest part to it, which is an atom
Since everything has a small part to it, you can predict that their are types of charges.
An atom has several charges, not smaller parts to it.
Atoms charges can be electron, neutron and proton.

Answer 2

Because the atoms of ALL elements have the SAME smaller particles
such as electrons. If you don't have the whole atom, with the right number
of each particle bound together, then you don't have THAT ELEMENT.
You may have a different element, or no element.

Cars are made up of smaller particles, such as spark plugs, tires, and
steering wheels. But if you don't have the right number of each particle,
assembled in the right way, then you don't have the make and model of
the car, and you may not have a car at all.