An atom is so small that a single drop of water contains more than a billion atoms. Although tiny, atoms are mostly empty ...

Everyone at that time imagined the atom as a "plum pudding ... emitted by the radioactive element radium) at a sheet of gold foil only 1/3000 of an inch thick, and tracing the particles' paths.

It also tells us that chlorine has 18 neutrons (35 - 17) and, as the number of electrons and protons are equal in a neutral atom ... isotopes are forms of an element that have the same number ...

Heavy element researchers have been keen to lock down ... By pinning down the berkelium atom, the team could test its electronic structure model using ultraviolet–visible–near-infrared spectroscopy.

Players read questions about energy levels and score points by picking the correct element as ... This energy level model shows two electrons on the first energy level and six electrons on the second ...

He showed that every radioactive element decreases in radioactivity ... He discovered the atomic nucleus and developed a model of the atom that was similar to the solar system.