For the longest time, atoms were thought to be the smallest, most indivisible particle that materials were made of. Recently, it has been found that atoms can be further divided, but are still the smallest intrinsic part of an element that gives it certain properties.
It is easy to understand the structure of an atom if you image the solar system.
The atom has a central large nucleus which is positively charged and is solely made up of photons (positively charged particles). The nucleus of the atom is like the sun at the center of our solar system! As the planets in the solar system revolve around the sun in an elliptical path, electrons which are negatively charged particles, revolve around the nucleus and are held together in a set path by the forces of attraction that exist between the negatively charged electrons and the positively charged nucleus.
Did you know? Just like the sun makes up most of the mass in the solar system, 99.9% of the mass of an atom is concentrated in the nucleus!