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460 BCE
Democritus (460 B.C.- 370 B.C.)
He believed that atoms were indivisible and indestructible.
His ideas didn’t explain chemical behavior
Lacked experimental support because it wasn’t based on the scientific method. -
Antoine Lavoisier (1743-1794)
He was the first person to make oxygen. He also rearranges water to make it HgO to Hg+O. Antoine Lavoisier also made the Law of Conservation of Mass, It states that matter can't be created or destroyed. -
John Dalton (1766-1844)
He found out how elements are made up of tiny indivisible particles called atoms
Atoms of different elements are different from any other element
Atoms of different elements can chemically mix together or can combine in whole number ratios to form compounds
Chemical Reactions occur when atoms are separated or joined or rearranged. Atoms of one element can never be changed into atoms of another element result of a chemical reaction -
Eugen Goldstein (1850-1930)
He found the protons that have a positive charge. How he found this out was he knew there were electrons and a negative charge coming from one direction. He also saw that there was something else coming from the other direction and that was protons -
Dmitri Mendeleev (1834-1907)
He is known for the discovery of the periodic law and creation of the periodic table of elements.
He introduced his discovery of the periodic law in 1869.
He is highly recognized for his formulation of the periodic table of elements.
He discovered periodic law and the table of elements during research for the writing of his book, The Principles of Chemistry. -
J.J Thomson (1856-1940) BC
He identified the negative charged electrons in a ray tube (1897)
He figured out that the electrons were a component of all matter and it can be calculated the charge to mass ration for the electrons
He also created a model called plum pudding, in this model the volume of the atom is made up of more mass that is larger that the atom. -
Max Planck (1858-1947)
He studied at the Universities of Munich and Berlin, receiving his doctorate in philosophy.
His earliest work was on thermodynamics, and that eventually led him to work on the quantum theory.
He published his work in 1900 on the ‘revolutionary’ idea that the energy emitted by a resonator could only take on discrete values or quanta. The energy for a resonator of frequency v is hv where h is a universal constant, currently called Planck’s constant. -
Robert Millikan (1868-1953)
He carried out experiments to find the quantity of charge carried by an electron.
His values for electron and mass are very similar to those accepted today.
An electron carries exactly one unit of negative charge, and it’s mass is 1/1840 the mass of a hydrogen atom. -
Ernest Rutherford (1871-1937)
He and his coworkers decided to test what was then the current theory of atomic structure. He thought the alpha particles in his experiment should’ve passed easily through the the gold with only a slight deflection, but they passed straight through the gold atoms with no deflection. His model is called the nuclear atom. In the nuclear atom, the protons and neutrons are located in the nucleus, & the electrons are distributed around the nucleus & occupy almost all the volume of the atom. -
Henry Moseley (1887-1915)
He found in 1913 the positive charge on the nucleus.
When he did that the periodic table was rearranged by using the atomic number instead of the atomic mass, it shows how the elements were increasing. -
Niels Bohr (1885-1962)
He first discovered that electrons travel in separate orbits around the nucleus. The number of electrons on the outside determines the element.
He also showed the atom really small it had a positive charge to the nucleus that surrounded by the electrons. -
Erwin Schrodinger (1887-1961)
His great discovery, Schrodinger’s wave equation, was made during the first half of 1926.
The discovery was made because he was dissatisfied with the quantum condition of Bohr’s orbit theory and the fact that he believed that atomic spectra should be determined by a kind of eigenvalue problem. -
Werner Heisenberg (1901-1976)
Heisenberg formulated a type of quantum mechanics in 1925, and in 1927 he set the limits for how accurately the position and velocity of a particle can be determined by proposing the “uncertainty relation. -
James Chadwick (1891-1974)
He discovered the Neutron.
He found them in the nucleus with the protons.
They have the same mass as the protons.
The neutrons have no charge
