Properties of electrons
Electrons are elementary particles with a negative elemental charge, and a very small mass. An elementary particle is a particle which is not currently known to consist of other smaller particles. Protons and neutrons on the other hand consist of smaller particles such as quarks, and are not elementary particles.
Below you can see a comparison of the different particles of an atom.
Around every nuclei, there are an equal amount of electrons as there are protons in the nuclei. Since the electrons are negatively charged, they will repel each other. This means that electrons distribute themselves in a way that they are as far as possible from each other, which has consequences for how chemical bonds work. At the same time, there is a driving force that makes the electrons stay as close to the nuclei as possible, since the proton's positive charge attracts them.
Electrons are found in electron shells
Electrons move extremely quickly around the atomic nuclei. It is in principle impossible to predict exactly where they are at a certain point in time, but you can rather describe a probability of where they would be. The electrons of the atom can be said to exist in spherical electron cloud. There are certain places where it is more probably for electrons to be, which in the Bohr atomic model are called electron shells. The electrons in the outer electron shell are called valence electrons, and are especially important for the properties of the atom.
The next article in the series is about electron shells.