An atom is a fundamental piece of matter which were proposed around 400 B.C. by a Greek philosopher Democritus. An atom is made up of three kinds of particles and they are electrons, neutrons, and protons. The neutrons do not carry any charge the protons carry a positive charge and electrons carry a negative charge. The neutrons and the protons are inside nucleus and the electrons fly around above the nucleus. First of all, Ernest Rutherford was a chemist and also he is known as the father of nuclear physics. He was born on 30 August 1871, in New Zealand. He discovered an atomic model called planetary model in 1911. He was the first scientist that discovered that atoms have a small charged nucleus and they are circled by electrons and it became known as the planetary model of the atom. Also, he discovered proton in 1919. Also, Ernest Rutherford tested Thomson’s hypothesis by devising the gold foil experiment. In this model the protons and electrons are mixed throughout the atom. Ernest Rutherford said that then the mass of the atom was spread out throughout the atom if Thomson’s model was correct He reasoned that the only way the alpha particles could be deflected backwards was if most of the mass in an atom was concentrated in a nucleus. Then, Rutherford developed the planetary model. He assimilate atoms to plants. For example the protons and neutrons are in the middle of atom, like sun and the electrons orbited around the nucleus like planets. Also, Erwin Schrodinger has contributed to chemistry. He was born in Vienna, Austria,on 12 August 1887. He was a Nobel Prize-winning Austrian theoretical physicist who came up with a groundbreaking wave equation for electron movements and changed the face of quantum theory. Electron cloud model(it is also called the modern model of atom) is the latest model of atom. ?t discovered in 1926. The model is used to describe the possible locations of electrons around the nucleus. ?n orbitals dense nucleus surrounded by a cloud of electrons at various levels. Orbital is the place where an electron is likely to be found in an atom. ?t is different from Rutherford’s atomic theory because Rutherford’s atomic model it treats electron energy levels as clearly defined orbital paths around the nucleus like planets orbit the sun. However, the electron cloud model treats the energy levels as clouds. For Erwin Schrodinger the shapes of the clouds are based on the shapes formed by electrons that are trapped. ?n addition, the neutron was discovered in 1932 by the English physics James Chadwick in the 1930’s.He was was born on 20th October 1891 in Cheshire, England. His father is John Joseph Chadwick and his mother is Anne Mary Knowles. He graduated from the Honours School of Physics in 1911. Then, he went to Physical Laboratory under Professor Rutherford in the in 1912 and 1913, where he worked for radioactivity problems in Manchester. Rutherford forced Chadwick to do some experiments about neutrons. He thought that if the protons occupy the center of an atom, then since charged particles would repel each other and the structure of atoms would eventually be destroyed. However, the atom existed and it had a structure. ?f that was so, Chadwick understood that there are some other particles that holds protons together. His findings were accepted by Werner Heisenberg. Chadwick showed that the neutron is different from protons and electron so they accepted that the third piece of the atom to be found. Neutron do not carry any charge like protons and electrons. For example protons carry positive charge and electrons carry negative charge. Although, neutrons are neutre particles.