The elements of the periodic table are all different types of atoms that make up the structural basis for all existence. There are over 100, and each element (atom) contains a small dense positive charge, known as the nucleus of the atom. Outside the nucleus is a relatively much lighter orbiting cloud of negatively charged electrons. For every electron there is a mutual proton (a positively charged particle)in the nucleus as well to balance the charge of the atom, and it is in the number of protons that an atom finds its uniqueness and identification. For instance, one of the most common of all elements in the universe is hydrogen. Hydrogen has 1 proton, 1 electron, and sometimes 1 or 2 neutrons (neutrally charged particles, also found in the nucleus). Since it has 1 proton, it is given the number 1 on the periodic table.
The electrons in orbit around each element dictates not only its location on the table, but also how it interacts with other elements. Each element has a set of orbits of electrons surrounding in it, and depending on the number of electrons and the orbitals they occupy, determines what it shares its electrons with. The periodic table is split this way to distinguish between elements that are electron deficient (left side; alkaline and earth metals), also deficient but all have an incomplete d-orbital (middle; transition metals), electron rich (right side; nonmetals), and full orbitals and therefore incapable of reacting (far right; halogens).
As mentioned before each element has a cloud of electrons surrounding it, and depending on that number dictates how it behaves and interacts with other elements. There are four different orbitals that electrons can occupy: S, P, D, and F. The s-orbital requires two electrons to become full, while the p orbital requires six, the d-orbital needs ten, and the f-orbital can take to fourteen! The f-orbital is used only by elements of rare usage and artificial creation in the lab and can be worried about in college. The number of electrons fill these orbitals is dependant on the element’s atomic number. Hydrogen has an atomic number of 1, meaning it has one electron. This one electron goes to fill to the s-orbital half way. Each pair of electrons that orbit an element requires one to be “spinning up” while the other electron “spins down” to create stability for the atom. An overall rule on how chemistry and all the world works is everything wants to find the state of most stability, which means an atom is most happy with a full pair of electrons to stabilize it. Since hydrogen only has one electron it is rarely found just as mono-atomic Hydrogen, but instead H2. Existing as this diatomic element found in abundance in the atmosphere would be highly reactive if split into just one hydrogen.
The next element after hydrogen is helium and it has an atomic number of two, with two electrons filling the s-orbital. No loose electrons, which means helium should be very stable? Not only is helium very stable but all the elements that share a column with it also share this full orbital configuration (starting to notice a pattern to the periodic table?) As you travel down the periodic table (and up in atomic numbers) the more orbitals like p and d get filled. The electrons are distributed as such (with the leading number representing the orbital number and the last number showing the number of electrons): 1S2 2S2 2P6 3S2 3P6 4S2 3D10 4P6 4D10 4F14 There is an occasional exception along the way of how the electrons are distributed for an occasional element, otherwise the periodic table serves as an excellent way to quickly determine the orbital of an element based on trends in the table.