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400 BCE
Democritus
Democritus was an ancient Greek philosopher, popularly recognized as the Father of Modern science. With the influence of his mentor Leucippus, he developed the world's first atomic theory.
1. Everything is made up of tiny, geometrically indivisible particles (atoms).
2. Atoms are indestructible and forever in motion.
3. There are infinite numbers of atoms in different shapes and sizes. -
Dalton
Dalton was an English chemist and schoolteacher. Dalton's Atomic Theory:
1. All elements are made of atoms: tiny, indivisible particles.
2. Atoms of the same element are identical, and atoms of one element are different from those of any other element.
3. Atoms of different elements can only physically mix together or combine chemically to form compounds.
4. By separating atoms or rearranging their orders, chemical reactions occur, but atoms don't turn into atoms of other elements. -
J.J. Thomson
J.J Thomson was an English physicist who used cathode-ray tubes to deduce the existence of a negatively charged particles, later to be named the electron. After discovering the electron, he proposed the pudding model of the electron. Cathode Ray Tube Experiment -
Marie and Pierre Curie
In addition to being a renowned married couple, Marie and Pierre Curie were grounding breaking chemists, best known for their work with uranium and thorium and their discovery of the elements radium and polonium. Marie Curie coined the term radioactivity, the spontaneous emission of rays and particles emitted from a radioactive source. -
Max Planck
Max Planck was a theoretical physicist and professor at the University of Berlin. By attempting to explain the correlation between color change and heat, he discovered that if atoms are vibrated with enough power, the energy of a body only changes and can be measured in quanta, or small, discrete units. Planck determined the equation Energy= h times frequency of radiation, where h is a constant value known as Planck's Constant. -
Hantaro Nagaoka
Hantaro Nagaoka was a professor of physics at the Imperial University in Japan. He offered the idea of a nuclear structure in 1903, releasing a model known as the Saturnian model of the atom. According to this model, the atom has a massive positive center with orbiting electrons, like Saturn and its rings. -
Albert Einstein
German Theoretical Physicist Albert Einstein was the first to prove that atoms existed through a microscope. Using Brownian motion, and some related mathematics, Albert could accurately calculate the average distance an immersed visible particle would travel in a given amount of time. The mathematical laws over the invisible particles, or atoms, movement could be measured and tested by using larger particle to observe. -
Hans Gieger
Hans Geiger was a German physicist who worked with Ernest Rutherford to develop a counter for alpha particles. The counter and other radiation detectors were used in experiments that led to the identification of alpha particles as the nucleus of helium atoms. This proved Rutherford’s proposal that, in any atom, the nucleus has a small volume in the center. -
Rutherford
In 1911, Rutherford collaborated with Hans Geiger and Ernest Marsden to perform an experiment to determine the structure of an atom. It is referred to as the Gold Foil Experiment, where alpha particles are aimed and “fired” at thin gold sheet of foil. The results of the tests are expressed in the nuclear model, in which protons and neutrons make up a nucleus with electrons distributed around it. -
Niels Bohr
In 1913, Niels Bohr, a Danish physicist, suggested a “planetary model” of the atom, where electrons orbit around a nucleus of protons and neutrons. The model is based on the belief that electrons travel in certain shells around the nucleus. Unfortunately, Bohr’s model only works with systems containing one or less electrons. -
Francis Aston:
Aston British physicist and chemist. He invented the mass spectrograph and discovered the isotopic complexity of the elements
Aston Constructed the first velocity focusing mass velocity.
He along with JJ Thompson first detected isotopes -
Louis de Broglie
-A French physicist
-Made contributions to the experimental study of the atomic nucleus
-Developed the Theory of wave/particle duality
-Developed theory of electron waves
-He theorized that matter on the atomic scale might have the properties of a wave-This was based off of Einstein’s earlier suggestion that light of short wavelengths might under some conditions be observed to behave as if it were composed of particles -
Werner Heisenberg and Erwin Schrodinger (Electron Cloud Model)
Together, they established the Heisenberg uncertainty principle. Schrodinger:
-Discovered his partial differentiation equation that is the basic equation of quantum mechanics
-Proposed that particles of matter have an dual nature and in some situations act like waves
-introduced a theory describing the behavior of a system by a wave equation called Schrodinger equation
-Solutions to Schrodinger’s equations are wave functions that can only be related to probable occurrence of physical events -
James Chadwick
James Chadwick was a English physicist
He joined Ernest Rutherford in accomplishing the transmutation of other light elements by bombardment with alpha particles, as well as making studies of the properties and structure of atomic nuclei
He proved the existence of neutrons( elementary particles devoid of any electrical charge)
Through discovery of the neutron, he led the way to the fission of uranium 235 and towards the creation of the atomic bomb. -
Glean Seaborg
Seaborg was an American nuclear chemist known for his work on identifying transuranium elements(those heavier than Uranium
Seaborg along with Author Wahl, and Joseph Kennedy, produced and identified the second known transuranium element , plutonium.
Over the next 14 years, Seaborg and his co-workers discovered these new elements: Americium(95), Curium(96), Berkelium(97), Californium(98),Einstinium(99), Fermium(100), Mendelorium(101).
