Atomic theory states that everything consists of trillions of inseparable particles, called atoms. Atoms have a core, consisting of neutrons and protons. The neutrons have a neutral charge, while protons have positive charge. Orbiting these neutrons and protons are electrons, and they have a negative charge. Each element has the same number of protons and electrons so that the system has a neutral charge.
If you didn't already know, each number corresponds to the elements' atomic number. For example, Hydrogen's atomic number is one. This means that it has one proton in its core and one electron orbiting around. The number of neutrons can vary. Giving an atom different amounts of neutrons will result in different ions of the element.
New elements like ununoctium are being discovered in the century and these are incredibly dense atoms that can only be created in labs.
There is also a special pattern that electrons orbit in.
As you can see, each ring is called shell. Electrons are placed in each shell starting from the innermost one and when it is full, they move onto the next. Elements on the rightmost side are called Noble Gases. They are special because they always have a completed electron shell.
Helium has two electrons, so its first shell is completed, with no leftovers.
Neon has ten electrons, so its first and second shell are completed, (2+8) with no leftovers.
And on and on.
These elements are chemically inert, which means that it is almost impossible for them to create chemical reactions or bonds.
The column to the left is labelled halogens and they are also special, Unlike noble gases, they are missing just one electron to become inert. That is why they are highly reactive, because they just want that last electron.
The far left column excluding Hydrogen consists of the Alkali Metals. All of these are soft, highly reactive metals. Unlike Halogens, they have an electron and they just want to get rid of it ASAP. They usually form bonds with halogens because they have an extra electron and halogens need one electron. An example is NaCl, or table salt. Chlorine lends an electron to sodium so they can be chemically stable, and everyone is happy.
