-
Robert Boyle performs experiments
In 1658 the Irish chemist Robert Boyle performed a series of experiments on air, after which he concluded that all matter was composed of solid particles arranged into molecules, which combinations gave the matter its different properties. -
Problems arise from Chemistry
In The Sceptical Chymist (1661), Boyle demonstrates problems that arise from chemistry, and offers up atomism as a possible explanation. -
Gravity
Kinetic Theory of Gravity proposed by Nicolas Fatio de Duillier in 1690. -
Georges-Louis Le Sage
Kinetic Theory of gravity was proposed once again by Georges-Louis Le Sage. -
Law of Conservation of Mass
Near the end of the 18th century, two laws about chemical reactions emerged without referring to the notion of an atomic theory. The first was the law of conservation of mass, formulated by Antoine Lavoisier in 1789, which states that the total mass in a chemical reaction remains constant (that is, the reactants have the same mass as the products). -
Law of Definite Proportions
First proven by the French chemist Joseph Louis Proust in 1799, this law states that if a compound is broken down into its constituent elements, then the masses of the constituents will always have the same proportions, regardless of the quantity or source of the original substance. -
Atomic weights
In 1803 Dalton orally presented his first list of relative atomic weights for a number of substances. This paper was published in 1805. -
Atomic Theory by John Dalton 1803-1807
A meaningful atomic theory was finally published during the period 1803-1807 by John Dalton -
Dalton
Dalton's particular contribution, which distinguished his work from what had been done before, was his method for actually determining atomic weight. In an essay published in 1805, Dalton had included a list of atomic weights for 21 elements. Dalton was also the first to propose standard symbols for the elements. -
A New System of Chemical Philosophy
Dalton published a full account in his own textbook, A New System of Chemical Philosophy, 1808 and 1810. -
Periodic Law
In 1869, the Russian chemist Dmitri Mendeleev and the German chemist Julius Lothar Meyer independently announced the discovery of a periodic law. They observed that when elements were listed according to their atomic weights, elements with similar properties appeared at regular intervals, or periods. -
Basic Atomic Theory
In 1895 the German Wilhelm Rontgen discovered X-rays, and in 1896 Frenchman Henri Becquerel discovered radioactivity in uranium. Their work was further advanced by French pioneers Marie and Pierre Curie later in the decade. These would lead to radical alterations/refinements in the basic atomic theory. -
The Electron
Modern theories about the physical structure of atoms did not begin until 1897, with J. J. Thomson's discovery of the electron. -
Scientists base studies off of earlier information
Since Thomson's discovery of the electron in 1897, scientists had realized that an atom must contain a positive charge to counterbalance the electrons' negative charge. -
Goldstein discovered protons
E. Goldstein (1900) discovered protons in Anode Ray experiments. According to Goldstein, atoms contain positively charged particles called protons. Since atoms contain negatively charged particles, they must contain positively charged particles for them to be electrically neutral. -
Millikan's Oil Drop Experiment
Found the charge of the Electron -
The Nucleus
E. Rutherford (1911) discovered the nucleus and provided the basis for the modern atomic structure through his alpha particle scattering experiment. -
Rutherford
In 1911, Rutherford proposed a revolutionary view of the atom. He suggested that the atom consisted of a small, dense core of positively charged particles in the center (or nucleus) of the atom, surrounded by a swirling ring of electrons. -
Quantom Theory
Quantum theory revolutionized physics at the beginning of the 20th century, when Max Planck and Albert Einstein postulated that light energy is emitted or absorbed in discrete amounts known as quanta (singular, quantum). In 1913, Niels Bohr incorporated this idea into his Bohr model of the atom, in which an electron could only orbit the nucleus in particular circular orbits with fixed angular momentum and energy, its distance from the nucleus being proportional to its energy. -
Nuclear Particles
In 1917 Rutherford bombarded nitrogen gas with alpha particles and observed hydrogen nuclei being emitted from the gas (Rutherford recognized these, because he had previously obtained them bombarding hydrogen with alpha particles, and observing hydrogen nuclei in the products). -
Models of the Atom
In 1924, Louis de Broglie proposed that all moving particles — particularly subatomic particles such as electrons — exhibit a degree of wave-like behavior. Erwin Schrödinger, fascinated by this idea, explored whether or not the movement of an electron in an atom could be better explained as a wave rather than as a particle. -
Bohr
N. Bohr (1940) provided the modern concept of the atomic model. According to Bohr, the atom is made of a central nucleus containing protons (positively-charged) and neutrons (with no charge). The electrons (negatively-charged) revolve around the nucleus in different imaginary paths called orbits or shells. -
The beginning of the 20th century
Not until the beginning of the 20th century the atomic theory was finally approved as a fact, not a mere hypothesis. It was accomplished by the skilful experiments of the French physicist Jean Baptiste Perrin. -
A new view on atoms
UCLA researchers report in the April 30 edition of the journal Cell that they have imaged a virus structure at a resolution high enough to effectively "see" atoms, the first published instance of imaging biological complexes at such a resolution. -
Nanoparticles
electron-microscopic study, which was published in the journal Nature on 17 February 2011.
-For the first time, scientists have managed to measure the atomic structure of individual nanoparticles
