Atomic Models - Early Atomic Theory, Discovery Of The Electron, The First Atomic Models, Discovery Of The Proton

Atomic Models - Early Atomic Theory

Atomic models have their beginnings in the early atomic theory. The law of conservation of mass, the law of definite proportions, and the law of multiple proportions, provided models for the behavior of chemical reactions, but the laws could not be explained. In 1808, John Dalton (1766–1844) proposed his atomic theory, which served as an explanation for these phenomena. His theory consists …

Atomic Models - Discovery Of The Electron

The discovery of the first subatomic particle, the electron, resulted from experiments involving the effects of electricity on matter. In the late 1800s, the cathode ray tube was developed and used in several investigations. A cathode ray tube is a partially evacuated glass tube containing a gas at low pressure. At one end of the tube is a cathode, at the other end, an anode. The cathode and anode…

Atomic Models - The First Atomic Models

Thomson used these results to formulate his "plum pudding" model of the atom between the years 1903–1907. This model was an adaptation to a similar model first proposed by Lord Kelvin (1824–1907) in 1902. According to this model, the negatively charged electrons of an atom are found within a positively charged material, much like plums embedded in plum pudding. If one o…

Atomic Models - Discovery Of The Proton

Atomic Models - Discovery Of The Neutron

The discovery of the proton resulted in another mystery. The mass of the hydrogen atom was known to be larger than the mass of a proton and an electron added together. Scientists searched for the source of the missing mass by assuming that another particle must exist in the nucleus of the atom that also contributes to the mass of the atom. This particle must be neutral in charge, since the positiv…

Atomic Models - The Dual Nature Of Matter

Even with the discovery of the proton, Rutherford's atomic model still did not explain how electrons could have stable orbits around the nucleus. The development of a mathematical constant by the German physicist Max Planck (1858–1947) served as the basis for the next atomic model. Planck developed his constant in 1900 when explaining how light was emitted from hot objects. He hypoth…

Atomic Models - The Bohr Model Of The Atom

In 1913, the Danish theorist Niels Bohr (1885–1962) developed his quantized shell model of the atom. Bohr modified Rutherford's model by hypothesizing that the electrons orbit the nucleus in specific regions of fixed size and energy. The energy of the electron depends on the size of the orbit. Electrons in the smallest orbits have the least energy. An atom is stable when its electron…

Atomic Models - The Modern Atomic Model

The development of quantum mechanics served as the foundation of the modern atomic theory. In 1922, the American physicist Arthur H. Compton (1892–1962) conduced x-ray scattering experiments that confirmed and advanced Einstein's theory on the dual nature of light. In 1923, the French physicist Louis-Victor de Broglie (1892–1987) expanded on this theory by proposing that all m…