The atom is the most basic unit of matter, it is the building block of the world we live in. Every element has it's own unique type of atoms. The atoms are composed of a nucleus surrounded by dense clouds of orbitals containing electrons, which are negatively charged. Within the nucleus there are protons, which are positively charged, and neutrons, which are neutrally charged. The electrons are kept in place on their orbitals by electromagnetic forces.
There were many theorized models of the atom. Some of the better known models were the Bohr model, and the plum-pudding model. Most of these models were proved incorrect, but they sparked the quest of truely understanding the complex atom.
Atoms are classified by the number of protons and neutrons, with their atomic number. The atom and it's protons and neutrons make up the identity of the element. The atom was discovered by Democritus who deemed it with it's name that means not able to cut in Greek. Even though it has been proved that it can be cut since, the name stuck, but it is true that it is the smallest part that retains the elements properties.
J.J. Thomson, who lived from 1856-1940, made experiments where he developed the cathode ray and discovered electrons. He used glass tubes and passed electrical currents through gases at low pressure. E. Goldstein discovered protons when he observed a cathode ray and found rays following the opposite directions then that of the cathode rays. James Chadwick discovered neutrons.
Quantum mechanics were used to model the atom when it was found that it wasn't the smallest possible part. It takes such devices as a scanning tunneling microscope. With devices like this scientists were able to view all the parts of the atom. The nucleus of an atom contains 99.9% of it's mass.
If an element has one or more isotopes, an unstable nuclei can lead to radioactive decay. There are three types of radioactive decay- there is alpha decay, beta decay, and gamma decay. Alpha decay is when the nucleus emits an alpha particle. Beta decay is when the nucleus emits beta particles, and gamma decay is when the nucleus emits gamma particles. The time period that it takes is called half-life.
Almost everything on earth is made up of atoms. It has been one of the most important discoveries in chemistry, and in science. It is the backbone of almost everything and as scientists continue the research of the world, the atom continues to help discover amazing things.