Atoms
Atom is the fundamental building block of all stuff, or what scientists like to call "matter". An individual atom is very small. In fact, the smallest type of atom, hydrogen, has a diameter of 10-8 cm. Every single object is composed of atoms. Our body is made up of many, many individual atoms. There are also many different types of atom. These different types are called elements. Examples of some elements are hydrogen, oxygen, and helium. Under normal conditions many atoms can stick together to form larger, different stuff. Scientists call material that results from the joining of different types of atoms "compounds". Atoms are not the smallest things there but are made up of still smaller stuff. Also, atoms can be broken apart …show more content…

Such atoms are called positive or negative “ions.” J.J. Thomson (1856-1940), an English physicist, and colleagues, discovered that the negatively charges are tiny particles, each with the same ratio of charge to mass. His experiment is consists of a tube from which some of the air is evacuated and which has metal at each end. If a voltage is applied between the ends, charged particles are emitted from the negative end, called the “cathode,” and travel to the positive end, called the “anode.” The charged particles emit electromagnetic radiation when striking the residual air molecules in the tube, thereby enabling the path of the particles to be seen. Thomson showed that the particles were deflected by a magnet, thereby proving that the particles were electrically charged. The direction of deflection showed that the charges were negative. By measuring the amount of deflection caused by the known magnetic field of the magnet and by measuring the strength of a transverse electric field required to eliminate the deflection, Thomson was able to determine the ratio of the electric charge c to the particle mass m. He found that all the particles had the same ratio of c or m, as if all of them were identical. The particle is called the electron, and was discovered by Thomson in 1897. It is the first particles discovered and the only one discovered in the 19th century. Thomson proposed a model of the atom, called the “plum pudding” model. According to his