Electron Shells
The properties of electron shells, or orbitals, help determine the c
Electrons captured in an atom don't fly around in circles as they are often depicted, but rather exist in a particular area around the atom.
Electrons "orbit" at quite a distance relative to the nucleus of protons and neutrons. They don't orbit the nucleus as a planet orbits a star, but due to quantum mechanics, they have a probability of existing on the surface of an area enclosing or near the nucleus. This area is called a shell or orbital.
All the shells follow a particular pattern as atoms get bigger and bigger. This pattern is the same for every atom, and electrons could be found in any of the shells, but electrons tend to fall into the available shells with the lowest energy levels. These happen to be the shells closest to the nucleus. As those shells fill up, the shells further away are used. The further away a shell is from the nucleus, the more electrons it can hold. In fact, the number of spots available for electrons is determined by the square of the shell number times 2. So the first shell can hold 2 electrons, and the fourth shell can hold 32 electrons.
The number of electrons that the atom can support is determined by the number of protons in the atom. The cumulative positive charge of all the protons in the nucleus of an atom attract negatively charged electrons.
Hydrogen and helium have a single spherical shell available that encases the nucleus. Hydrogen's single proton supports a single electron. Helium's two protons support two electrons. Slightly larger elements have an additional spherical shell. After that the shells take on odd shapes. Some look like dumbbells, pinched spheres, or stacks of doughnuts.
The outside shell of any atom is called the valence shell. The properties of this shell help to determine the chemical properties of the atom. Shells closer to the nucleus have little interaction with the outside world, but the valence shell allows the atom to bond with other atoms. Electrons like to pair up, so a shell with unfilled spots available will attract electrons that also reside in the shells of other atoms. The more unfilled spots in the valence shell, the more bonds the atom can make.
The Orbitron is a great web tool for visualizing the shapes of shells.
