Students use the terms isotope, atomic number, mass number, and atomic mass. Atomic Theory: Structure of the Atom: Students use the terms isotope, atomic number, mass number, and atomic mass to ...

The idea of the atom as the building block of matter has developed over time. What was thought of as a single particle about 1 × 10‾¹⁰ m across is now known to be a collection of smaller particles.

The nucleus is very small compared to the atom as a whole: as electrons are even smaller, most of an atom is empty space the diameter of a nucleus can be 100,000 times less than the diameter of an ...