Leucippus of Miletus (5th century bce) originated atomic philosophy

his disciple Democritus of Abdera named building blocks of matter atomos, meaning literally “indivisible,” about 430 bce suggested sphere of elements (earth,air,fire and water)

aristotle Advocated for the idea of four elements (earth, air, fire, and water), leading to the atomic theory being largely ignored for almost 2000 years.

In 1738, Swiss physicist and mathematician Daniel Bernoulli postulated that the pressure of gases and heat were both caused by the underlying motion of molecules.

in 1789: Antoine Lavoisier redefined an element as a substance which scientists could not decompose into simpler substances by experimentation brought an end to the ancient idea of the elements of matter being fire, earth, air, and water, which had no experimental support he showed that water can be decomposed into hydrogen and oxygen, which in turn he could not decompose into anything simpler, thereby proving these are elements defined the law of conservation of mass

in 1797 law of definite proportions, established by the French chemist Joseph Proust if a compound is broken down into its constituent chemical elements, then the masses of those constituents will always have the same proportions by weight, regardless of the quantity or source of the original compound. This definition distinguished compounds from mixtures.

John dalton Thomas Thomson, who published an explanation of Dalton's theory in his book A System of Chemistry in 1807 book A New System of Chemical Philosophy (Part I, 1808; Part II, 1810) togather with Joseph-Louis Gay-Lussac of France and Amedeo Avogadro provided experimental foundation of atomic chemistry

  • All matter consists of extremely small particles called atoms.
  • Atoms are indestructible and resist changes. based on law of conservation of mass in late 1700
  • all atoms of an element are identical in shape, size, and mass.
  • they combine in small whole-number ratios to form what are now called molecules.

dalton studied data to notice law of multiple proportions , finding element combines with other elements in multiples of a basic quantity.

in 1811 Amedeo Avogadro Avogadro proposed that equal volumes of any two gases, at equal temperature and pressure, contain equal numbers of molecules (in other words, the mass of a gas's particles does not affect the volume that it occupies)

in 1869 Mendeleev's periodic table Dmitrii Mendeleev, Russian chemist and inventor noticed that when he arranged the elements in a row according to their atomic weights, there was a certain periodicity to them. noble gases were not known back when Mendeleev devised his table

Sir Joseph John (J.J) Thomson in 1897 , he discoverd electron , atom no longer homogeneous particle and has sub structure discoverd. evidence in favor “plum-pudding” model of atomic structure first proposed by Lord Kelvin.

  • there are pockets of negative charges within the sphere of the atom

experiment A Crookes tube is a sealed glass container in which two electrodes are separated by a vacuum. When a voltage is applied across the electrodes, cathode rays are generated, creating a glowing patch where they strike the glass at the opposite end of the tube. Through experimentation, Thomson discovered that the rays could be deflected by electric fields and magnetic fields, which meant that these rays were not a form of light but were composed of very light charged particles, and their charge was negative. Thomson called these particles "corpuscles". He measured their mass-to-charge ratio to be several orders of magnitude smaller than that of the hydrogen atom, the smallest atom. This ratio was the same regardless of what the electrodes were made of and what the trace gas in the tube was positive ions created by electrolysis or X-ray radiation had mass-to-charge ratios that varied depending on the material of the electrodes and the type of gas in the reaction chamber, indicating they were different kinds of particles

In 1898, Thomson measured the charge on ions to be roughly 6 × 10-10 electrostatic units (2 × 10-19 Coulombs) In 1899, he showed that negative electricity created by ultraviolet light landing on a metal (known now as the photoelectric effect) has the same mass-to-charge ratio as cathode rays he showed that electron's mass was 0.0014 times that of hydrogen ions. concluded they must be the basic particles of electricity since they are so light but has so much charge

1900: Max Planck Introduced the concept of quanta, the discrete units of energy, laying the groundwork for quantum theory. 1902 : Marie and Pierre Curie isolate radium, furthering the study of radioactivity. 1903: Henri Becquerel, Marie Curie, and Pierre Curie awarded the Nobel Prize in Physics for their work on radioactivity. 1904: J.J. Thomson proposes the "plum-pudding" model of the atom. 1905: Albert Einstein Explained the photoelectric effect, demonstrating that light can be understood as quanta of energy, or photons. Albert Einstein publishes his theory of special relativity. 1908: Ernest Rutherford awarded the Nobel Prize in Chemistry for his investigations into the disintegration of elements and the chemistry of radioactive substances. 1906-1909: Robert A. Millikan and Harvey Fletcher performed the oil drop experiment in which they measured the charge of an electron to be about -1.6 × 10-19, a value now defined as -1 e

1911: Rutherford model a former student of Thomson’s, New Zealand-born British physicist Ernest Rutherford, with other scientists, performed experiment that led to the overturning of Thomson’s model

alpha particle experiment aimed alpha particles at a thin sheet of gold foil and then recorded the location of the alpha particle with a fluorescent screen

  • the majority of the alpha particles passed through the gold foil as if the foil was not there.
  • a very small number of these alpha particles deflected at angles from the initial path
  • some of the alpha particles even bouncing back along the initial path.

conclusion : there must be a small, highly dense core of matter in an atom off which the alpha particles were bouncing. theorized that this atomic nucleus was positively charged and surmised that the electrons orbited around it.

Bohr model

quantum model of Arthur Erich Haas in 1910 and the 1912 John William Nicholson quantum atomic model that quantized angular momentum as h/2π

1912-1913: Henry Moseley begins work that will lead to the concept of atomic numbers. Henry Moseley discovered that atoms of each element, when excited, emit X-rays at a frequency proportional to the element's position on the adjusted periodic table

1913: student of Rutherford , bohr proposed his quantized shell model of the atom The motion of the electrons in the Rutherford model was unstable because, according to classical mechanics and electromagnetic theory, any charged particle moving on a curved path emits electromagnetic radiation; thus, the electrons would lose energy and spiral into the nucleus.

  • The energy and angular momentum of an electron depends on the size of the orbit (radius) and is lower for smaller orbits
  • each orbit has a different energy level associated with it, as the distance from the nucleus determines forces acting on the electrons in the various orbits, or shells
  • Radiation can occur only when the electron jumps from one orbit to another
  • energy can be absorbed by electrons to move from a lower energy orbit to a higher energy orbit and that they release energy when moving from higher to lower energy orbits

by the early 1920s Bohr’s model seemed to be a dead end, as efforts to generalize the model(explain spectral line) to multielectron atoms had proved futile it couldnt explain multiplication of spectral lines on applying magnetic field quantum atomic model

1914: James Franck and Gustav Hertz conduct experiments that confirm the existence of quantized energy levels in atoms.

1915: Albert Einstein's general theory of relativity published, impacting the field of physics.

1916: Gilbert N. Lewis introduces the concept of electron pairs and covalent bonds in his theory of chemical bonding.

1917: Ernest Rutherford achieves the first artificial nuclear reaction by bombarding nitrogen with alpha particles, transforming it into oxygen.

1918: Fritz Haber awarded the Nobel Prize in Chemistry for the synthesis of ammonia from its elements, a crucial process for fertilizers and explosives.

1919: Ernest Rutherford discovers the proton.

1920: Francis W. Aston uses the mass spectrometer to discover isotopes and formulate the whole number rule, which states that the masses of isotopes are whole numbers.

1921: Albert Einstein awarded the Nobel Prize in Physics for his explanation of the photoelectric effect.

1922: Niels Bohr awarded the Nobel Prize in Physics for his contributions to understanding atomic structure and quantum theory.

1923: Robert Millikan awarded the Nobel Prize in Physics for his work on the elementary charge of electricity and the photoelectric effect. Louis de Broglie proposes wave-particle duality for subatomic particles.

1924: Louis de Broglie formally introduces the theory of electron wave-particle duality.

1925: Austrian physicist Wolfgang Pauli formulated Pauli exclusion principle for electrons, and later extended to all fermions with his spin–statistics theorem of 1940. which states states that two or more identical particles with half-integer spins (i.e. fermions) cannot simultaneously occupy the same quantum state within a system that obeys the laws of quantum mechanics.

Werner Heisenberg and Erwin Schrödinger develop foundational aspects of quantum mechanics.

1926: Austrian physicist Erwin Schrödinger used mathematical equations to describe the probability of finding electrons in specific positions developing wave mechanics and the Schrödinger equation

1927: Werner Heisenberg introduced uncertainty principle .A consequence of describing particles as waveforms rather than points is that it is mathematically impossible to calculate with precision both the position and momentum of a particle at a given point in time.

1928: Walter Bothe observed that beryllium emitted a highly penetrating, electrically neutral radiation when bombarded with alpha particles Paul Dirac formulates the Dirac equation, predicting the existence of antimatter.

1930: Wolfgang Pauli predicts the existence of the neutrino to explain beta decay.

1931: Harold Urey discovers deuterium, an isotope of hydrogen.

1932: English physicist James Chadwick discovered a neutral particle of approximately the same mass as the proton and located in the nucleus of the atom called neutron Carl D. Anderson discovers the positron (antiparticle of the electron).

1933: Erwin Schrödinger and Paul Dirac awarded the Nobel Prize in Physics for their contributions to quantum mechanics. Enrico Fermi introduces the concept of beta decay and weak interaction theory.

1934: Enrico Fermi conducts the first artificial nuclear reactions, leading to the concept of nuclear fission.

1935: Frédéric Joliot and Irène Joliot-Curie awarded the Nobel Prize in Chemistry for their synthesis of new radioactive elements.

1936: Eugene Wigner develops the concept of nuclear shell structure.

1937: Discovery of technetium, the first artificially produced element by Carlo Perrier and Emilio Segrè.

1938: Otto Hahn and Fritz Strassmann discover nuclear fission in uranium. Lise Meitner and Otto Frisch explain the process of nuclear fission theoretically.

1939: Discovery of nuclear fission leads to the beginning of nuclear chain reactions research.

1940: Glenn T. Seaborg and Edwin McMillan discover neptunium, the first transuranium element.

1941: Glenn T. Seaborg Discovered plutonium and contributed to the discovery of many other transuranium elements, leading to significant advancements in nuclear chemistry.


Enrico Fermi and his team achieve the first controlled nuclear chain reaction in the Chicago Pile-1 reactor.


Otto Frisch and Rudolf Peierls calculate the critical mass of uranium-235 necessary for an atomic bomb.


Glenn T. Seaborg proposes the actinide concept, reorganizing the periodic table and predicting the properties of heavy elements.


The first atomic bombs are detonated in the Trinity test and used in warfare on Hiroshima and Nagasaki, Japan.


Hermann Joseph Muller awarded the Nobel Prize in Physiology or Medicine for his discovery of radiation-induced mutations.


Discovery of berkelium (element 97) and californium (element 98) by Seaborg's team at Berkeley.


Introduction of the "cloud chamber" to study charged particle paths, contributing to particle physics and atomic structure studies.


Discovery of einsteinium (element 99) and fermium (element 100) in the debris of the first hydrogen bomb explosion.


Eugene Wigner, Maria Goeppert Mayer, and J. Hans D. Jensen awarded the Nobel Prize in Physics for their work on the nuclear shell model.


Glenn T. Seaborg awarded the Nobel Prize in Chemistry for his discoveries in the chemistry of the transuranium elements.


Discovery of mendelevium (element 101) by Albert Ghiorso, Glenn T. Seaborg, and their team.


Discovery of nobelium (element 102) by teams in Berkeley and Dubna, though its synthesis is confirmed later.


Introduction of the hydrogen bomb (thermonuclear bomb), with fusion reactions enhancing atomic research.


Discovery of lawrencium (element 103) by Albert Ghiorso and his team.


Discovery of antineutrinos by Clyde Cowan and Frederick Reines, confirming the existence of neutrinos.


Discovery of elements 104 and 105, rutherfordium and dubnium, at Dubna and Berkeley.


John Bardeen, Leon Cooper, and Robert Schrieffer propose the BCS theory of superconductivity.


Discovery of the Mössbauer effect by Rudolf Mössbauer, observing recoil-free gamma-ray emission and absorption.


Theodore Maiman creates the first working laser, advancing studies of atomic and molecular spectroscopy.


Discovery of the strange quark by Murray Gell-Mann and George Zweig.


Introduction of the concept of quarks by Murray Gell-Mann and George Zweig.


Maria Goeppert Mayer and J. Hans D. Jensen awarded the Nobel Prize in Physics for their development of the nuclear shell model.


Murray Gell-Mann and George Zweig propose the existence of quarks, fundamental constituents of protons and neutrons.


Richard Feynman, Julian Schwinger, and Sin-Itiro Tomonaga awarded the Nobel Prize in Physics for their work in quantum electrodynamics (QED).


Discovery of the J/psi particle by teams at Stanford and Brookhaven, confirming the existence of the charm quark.


Steven Weinberg, Sheldon Glashow, and Abdus Salam propose the electroweak unification theory, leading to the Standard Model of particle physics.


First direct evidence of quarks from deep inelastic scattering experiments at SLAC.


Murray Gell-Mann awarded the Nobel Prize in Physics for his contributions to the theory of elementary particles, particularly quarks.


Discovery of the bottom quark by teams at Fermilab.


The Standard Model of particle physics is formulated, incorporating the electromagnetic, weak, and strong nuclear forces.


Bardeen, Cooper, and Schrieffer awarded the Nobel Prize in Physics for their theory of superconductivity.


Discovery of the tau lepton by Martin Perl's team at SLAC.


Discovery of the J/psi meson confirms the charm quark, leading to the "November Revolution" in particle physics.


Introduction of the tau neutrino, confirming the third generation of leptons.


Discovery of the bottom quark (b-quark) by the E288 experiment at Fermilab.


Discovery of charmed mesons, further confirming the existence of the charm quark.


Discovery of the gluon, the mediator of the strong force, in three-jet events at DESY.


Sheldon Glashow, Abdus Salam, and Steven Weinberg awarded the Nobel Prize in Physics for their contributions to the electroweak unification theory.


Discovery of the top quark (t-quark) predicted, though it is not observed until later.


Introduction of the Scanning Tunneling Microscope (STM) by Gerd Binnig and Heinrich Rohrer, allowing the visualization of individual atoms.


Nobel Prize awarded to Kenneth Wilson for his work on phase transitions and renormalization group theory.


Discovery of the W and Z bosons at CERN, confirming the electroweak theory.


Carlo Rubbia and Simon van der Meer awarded the Nobel Prize in Physics for the discovery of the W and Z bosons.


Discovery of the fullerenes (C60, buckyballs) by Harold Kroto, Richard Smalley, and Robert Curl.


Introduction of the atomic force microscope (AFM), enhancing the study of atomic and molecular structures.


Discovery of high-temperature superconductors by Johannes Georg Bednorz and Karl Alexander Müller.


Leon Lederman, Melvin Schwartz, and Jack Steinberger awarded the Nobel Prize in Physics for their work on neutrino beams and the discovery of the muon neutrino.


Tim Berners-Lee invents the World Wide Web, revolutionizing information sharing and collaboration in science.


Jerome Friedman, Henry Kendall, and Richard Taylor awarded the Nobel Prize in Physics for their experimental confirmation of quarks.


Discovery of the Bose-Einstein condensate, a new state of matter, by Eric Cornell, Carl Wieman, and Wolfgang Ketterle.


Nobel Prize awarded to Georges Charpak for his invention and development of particle detectors, particularly the multiwire proportional chamber.


Discovery of the top quark (t-quark) anticipated, though it is officially confirmed in 1995.


Nobel Prize awarded to Bertram Brockhouse and Clifford Shull for the development of neutron scattering techniques.


Discovery of the top quark (t-quark) confirmed by the CDF and DZero experiments at Fermilab.


Robert Curl, Harold Kroto, and Richard Smalley awarded the Nobel Prize in Chemistry for the discovery of fullerenes.


Steven Chu, Claude Cohen-Tannoudji, and William D. Phillips awarded the Nobel Prize in Physics for their development of methods to cool and trap atoms with laser light.


Discovery of neutrino oscillations by the Super-Kamiokande and Sudbury Neutrino Observatory, proving that neutrinos have mass.


Gerardus 't Hooft and Martinus Veltman awarded the Nobel Prize in Physics for their work on gauge theory and the Standard Model.


Discovery of the tau neutrino confirmed by the DONUT experiment at Fermilab.


Nobel Prize in Chemistry awarded to William S. Knowles, Ryōji Noyori, and K. Barry Sharpless for their work on chirally catalyzed hydrogenation and oxidation reactions.


Raymond Davis Jr. and Masatoshi Koshiba awarded the Nobel Prize in Physics for their work on detecting cosmic neutrinos.
Riccardo Giacconi awarded the Nobel Prize in Physics for contributions to astrophysics, which included the discovery of cosmic X-ray sources.


Nobel Prize in Physics awarded to Alexei Abrikosov, Vitaly Ginzburg, and Anthony Leggett for pioneering contributions to the theory of superconductors and superfluids.
Nobel Prize in Chemistry awarded to Peter Agre for the discovery of aquaporins and Roderick MacKinnon for his work on the structure and mechanism of ion channels.


Discovery of element 113 (Nihonium) by a team at RIKEN in Japan.
Nobel Prize in Physics awarded to David Gross, Frank Wilczek, and David Politzer for the discovery of asymptotic freedom in the theory of the strong interaction.
Nobel Prize in Chemistry awarded to Aaron Ciechanover, Avram Hershko, and Irwin Rose for the discovery of ubiquitin-mediated protein degradation.


The International Union of Pure and Applied Chemistry (IUPAC) recognizes the discovery of elements 111 (Roentgenium) and 112 (Copernicium).
Nobel Prize in Physics awarded to Roy Glauber for his contribution to the quantum theory of optical coherence and to John Hall and Theodor Hänsch for their contributions to the development of laser-based precision spectroscopy, including the optical frequency comb technique.


Discovery of the properties of graphene by Andre Geim and Konstantin Novoselov.
Nobel Prize in Physics awarded to John C. Mather and George F. Smoot for their discovery of the blackbody form and anisotropy of the cosmic microwave background radiation.
Nobel Prize in Chemistry awarded to Roger Kornberg for his studies of the molecular basis of eukaryotic transcription.


Nobel Prize in Physics awarded to Albert Fert and Peter Grünberg for the discovery of giant magnetoresistance.
Nobel Prize in Chemistry awarded to Gerhard Ertl for his studies of chemical processes on solid surfaces.


Discovery of element 114 (Flerovium) and element 116 (Livermorium) confirmed.
Nobel Prize in Physics awarded to Yoichiro Nambu for the discovery of the mechanism of spontaneous broken symmetry in subatomic physics, and to Makoto Kobayashi and Toshihide Maskawa for the discovery of the origin of the broken symmetry which predicts the existence of at least three families of quarks.
Nobel Prize in Chemistry awarded to Osamu Shimomura, Martin Chalfie, and Roger Tsien for the discovery and development of the green fluorescent protein (GFP).


The Large Hadron Collider (LHC) at CERN achieves its first collisions.
Nobel Prize in Physics awarded to Charles K. Kao for groundbreaking achievements concerning the transmission of light in fibers for optical communication, and to Willard S. Boyle and George E. Smith for the invention of an imaging semiconductor circuit – the CCD sensor.
Nobel Prize in Chemistry awarded to Venkatraman Ramakrishnan, Thomas A. Steitz, and Ada E. Yonath for studies of the structure and function of the ribosome.


Nobel Prize in Physics awarded to Andre Geim and Konstantin Novoselov for groundbreaking experiments regarding the two-dimensional material graphene.
Nobel Prize in Chemistry awarded to Richard F. Heck, Ei-ichi Negishi, and Akira Suzuki for palladium-catalyzed cross couplings in organic synthesis.


Discovery of element 117 (Tennessine) confirmed.
Nobel Prize in Physics awarded to Saul Perlmutter, Brian P. Schmidt, and Adam G. Riess for the discovery of the accelerating expansion of the Universe through observations of distant supernovae.
Nobel Prize in Chemistry awarded to Dan Shechtman for the discovery of quasicrystals.


Discovery of the Higgs boson by the ATLAS and CMS experiments at the LHC.
Nobel Prize in Physics awarded to Serge Haroche and David J. Wineland for ground-breaking experimental methods that enable measuring and manipulation of individual quantum systems.
Nobel Prize in Chemistry awarded to Robert Lefkowitz and Brian Kobilka for studies of G-protein-coupled receptors.


Nobel Prize in Physics awarded to François Englert and Peter Higgs for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles, and which recently was confirmed through the discovery of the predicted fundamental particle, by the ATLAS and CMS experiments at CERN's LHC.
Nobel Prize in Chemistry awarded to Martin Karplus, Michael Levitt, and Arieh Warshel for the development of multiscale models for complex chemical systems.


Nobel Prize in Physics awarded to Isamu Akasaki, Hiroshi Amano, and Shuji Nakamura for the invention of efficient blue light-emitting diodes which has enabled bright and energy-saving white light sources.
Nobel Prize in Chemistry awarded to Eric Betzig, Stefan W. Hell, and William E. Moerner for the development of super-resolved fluorescence microscopy.


Nobel Prize in Physics awarded to Takaaki Kajita and Arthur B. McDonald for the discovery of neutrino oscillations, which shows that neutrinos have mass.
Nobel Prize in Chemistry awarded to Tomas Lindahl, Paul Modrich, and Aziz Sancar for mechanistic studies of DNA repair.


Discovery of element 118 (Oganesson) confirmed.
Nobel Prize in Physics awarded to David J. Thouless, F. Duncan M. Haldane, and J. Michael Kosterlitz for theoretical discoveries of topological phase transitions and topological phases of matter.
Nobel Prize in Chemistry awarded to Jean-Pierre Sauvage, Fraser Stoddart, and Bernard Feringa for the design and synthesis of molecular machines.


Nobel Prize in Physics awarded to Rainer Weiss, Barry C. Barish, and Kip S. Thorne for decisive contributions to the LIGO detector and the observation of gravitational waves.
Nobel Prize in Chemistry awarded to Jacques Dubochet, Joachim Frank, and Richard Henderson for developing cryo-electron microscopy for the high-resolution structure determination of biomolecules in solution.


Nobel Prize in Physics awarded to Arthur Ashkin for the optical tweezers and their application to biological systems, and to Gérard Mourou and Donna Strickland for their method of generating high-intensity, ultra-short optical pulses.
Nobel Prize in Chemistry awarded to Frances H. Arnold for the directed evolution of enzymes, and to George P. Smith and Sir Gregory P. Winter for the phage display of peptides and antibodies.


Nobel Prize in Physics awarded to James Peebles for theoretical discoveries in physical cosmology, and to Michel Mayor and Didier Queloz for the discovery of an exoplanet orbiting a solar-type star.
Nobel Prize in Chemistry awarded to John B. Goodenough, M. Stanley Whittingham, and Akira Yoshino for the development of lithium-ion batteries.


Nobel Prize in Physics awarded to Roger Penrose for the discovery that black hole formation is a robust prediction of the general theory of relativity, and to Reinhard Genzel and Andrea Ghez for the discovery of a supermassive compact object at the center of our galaxy.
Nobel Prize in Chemistry awarded to Emmanuelle Charpentier and Jennifer A. Doudna for the development of CRISPR-Cas9, a method for genome editing.


Nobel Prize in Physics awarded to Syukuro Manabe and Klaus Hasselmann for the physical modeling of Earth's climate, quantifying variability and reliably predicting global warming, and to Giorgio Parisi for the discovery of the interplay of disorder and fluctuations in physical systems from atomic to planetary scales.
Nobel Prize in Chemistry awarded to Benjamin List and David W.C. MacMillan for the development of asymmetric organocatalysis.


Nobel Prize in Physics awarded to Alain Aspect, John F. Clauser, and Anton Zeilinger for experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science.
Nobel Prize in Chemistry awarded to Carolyn Bertozzi, Morten Meldal, and K. Barry Sharpless for the development of click chemistry and bioorthogonal chemistry.


Nobel Prize in Physics awarded to Pierre Agostini, Ferenc Krausz, and Anne L’Huillier for experimental methods that generate attosecond pulses of light for the study of electron dynamics in matter.
Nobel Prize in Chemistry awarded to Moungi Bawendi, Louis Brus, and Alexei Ekimov for the discovery and synthesis of quantum dots    

modern atomic model In the 1960s subatomic particles called quarks were found The proton is made up of two up quarks, each of which has a positive charge 2/3 that of the electron, and one down quark, which has a negative charge 1/3 that of the electron. The neutron is made up of one up quark and two down quarks and thus has no charge.