Electrons
An electron is a subatomic particle that is much smaller than the proton and neutron that inhabit the nucleus and it has a negative charge in contrast to the positively charged proton. The Electron was first discovered by J. J. Thomson in 1897 who figured out that they existed using his cathode ray tube experiments. Those experiments can be found here http://nuclearchem101.weebly.com/thomson-cathode-ray-tube-experiment.html. After concluding that these cathode rays were negatively charged particles that helped to make up an atom, he renamed them electrons. Electrons have a huge impact on the periodic trends that exist most of them being caused by an atom's electron configuration. This makes them instrumental in affecting some of the fundamental properties such as electron affinity and ionization energy. More about periodic trends can be found here http://nuclearchem101.weebly.com/periodic-trends.html. Every electron's position in an atom can be described by 4 quantum numbers which are described in more detail here http://nuclearchem101.weebly.com/quantum-numbers.html. Although electrons are comparatively small to protons and neutrons, neither electrons nor the protons and neutrons take up the most space in an atom. An atom is mostly empty space. After Dalton's discovery of the atom, the electron was the first subatomic particle to be discovered, and has remained relevant through the 20th century.