PRESENTATION OUTLINE
In 400 BC Greek philosophers, Leucippus and Democritus got together and said atoms are the building blocks of matter
In 1778 Antoine Lavoisier came around and discover the role oxygen plays in combustion and he invented the Law of Conservation of mass. The law of conservation of mass states that for any system closed to all transfers of matter and energy, the mass of the system must remain constant over time, as system mass cannot change quantity if it is not added or removed.
John Dalton came around in 1803 and he proved that elements exist in packets of matter.
Dalton's Atomic Theory
1) All matter is made of atoms. Atoms are indivisible and indestructible.
2) All atoms of a given element are identical in mass and properties
3) Compounds are formed by a combination of two or more different kinds of atoms.
4) A chemical reaction is a rearrangement of atoms.
Dmitri Mendeleev was a Russian chemist and inventor. He formulated the Periodic Law, created his own version of the periodic table of elements, and used it to correct the properties of some already discovered elements and also to predict the properties of eight elements yet to be discovered.
Henry Moseley was an English physicist. Moseley's outstanding contribution to the science of physics was the justification from physical laws of the previous empirical and chemical concept of the atomic number.
From 1898-1903, J.J. Thomson proved negative electrons are embedded in a sea of positive charge. J.J. Thomson invented the Cathode Ray Tube which is specialized vacuumtube in which images are produced when an electron beam strikes aphosphorescent surface.
The plum pudding model was a model of the atom that incorporated the recently discovered electron, and was proposed by J. J. Thomson in 1904. Thomson had discovered the electron in 1897. The plum pudding model was abandoned after discovery of the atomic nucleus. The plum pudding model of the atom is also known as the blueberry muffin model or the raisin bun model.
In 1910 Ernest Rutherford designed the Gold Foil Experiment and discovered that a positive charge is located within a central nucleus.
Ernest Rutherford was a New Zealand-born British physicist who became known as the father of nuclear physics. Encyclopædia Britannica considers him to be the greatest experimentalist.
In 1913 Neil's Bohr discovered that electrons are in circular orbits with quantized energy levels. In the Bohr Model the neutrons and protons occupy a dense central region called the nucleus, and the electrons orbit the nucleus much like planets orbiting the Sun.
The quantum mechanical model was discovered by Neil's Bohr, and is based on quantum theory, which says matter also has properties associated with waves. According to quantum theory, it’s impossible to know the exact position and momentum of an electron at the same time.
The quantum mechanical model of the atom uses complex shapes of orbitals.
Robert Millikan Robert was an American experimental physicist honored with the Nobel Prize for Physics in 1923 for his measurement of the elementary electronic charge and for his work on the photoelectric effect.
Between 1908 and 1917, Robert Millikan measured the charge on an electron with the apparatus. In his experiment, the atomizer from a perfume bottle was used to spray water or oil droplets into a sample chamber. Some of these droplets fell through a pinhole between two plates of an electric field, where they could be observed through a microscope.
Sir James Chadwick, CH, FRS was an English physicist who was awarded the 1935 Nobel Prize in Physics for his discovery of the neutron in 1932.
Erwin Schroedinger, was a Nobel Prize-winning Austrian physicist who developed a number of fundamental results in the field of quantum theory, which formed the basis of wave mechanics: he formulated the wave equation and revealed the identity of his development of the formalism and matrix mechanics. Schrödinger proposed an original interpretation of the physical meaning of the wave function.
The electron cloud model says that we can't know exactly where an electron is at any given time, but the electrons are more likely to be in specific areas. This is the most modern and accepted way to describe the situation.
These ideas were developed in 1925 by Erwin Schrödinger and Werner Heisenberg. The model provides the means of visualising the position of electrons in an atom.
