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Atomic Theory Timeline

(1803 - Present)

Explore the history of Atomic Theory with this comprehensive timeline, highlighting important scientific discoveries and advancements in our understanding of the atom. Less

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Ancient Origins

Increased scholarly attention on atomism

1300 - 1399

In the 14th century, the rediscovery of major ancient works describing atomist teachings led to increased scholarly attention on the subject, including Lucretius's De rerum natura and Diogenes Laërtius's Lives and Opinions of Eminent Philosophers.

Pierre Gassendi's modified theory of atoms

1600 - 1699

The French Catholic priest Pierre Gassendi revived Epicurean atomism with modifications, arguing that atoms were created by God and, though extremely numerous, are not infinite in number.

Image source: Atomic theory

Pierre Gassendi's modified theory of atoms

Popularization of Gassendi's theory in France and England

1600 - 1699

Gassendi's modified theory of atoms was popularized in France by the physician François Bernier and in England by the natural philosopher Walter Charleton.

Development and Acceptance

Defense and acceptance of atomism by Boyle and Newton

1600 - 1699

The chemist Robert Boyle and the physicist Isaac Newton both defended atomism, and by the end of the 17th century, the idea of an atomistic foundation of nature had become accepted by portions of the scientific community.

Laws of chemical reactions emerge

1775 - 1799

Near the end of the 18th century, two laws about chemical reactions emerged without referring to the notion of an atomic theory.

Joseph Proust's law of definite proportions

1797

First established by the French chemist Joseph Proust in 1797, this law states that if a compound is broken down into its constituent chemical elements, then the masses of the constituents will always have the same proportions by weight, regardless of the quantity or source of the original substance.

Image source: Joseph Proust

Joseph Proust's law of definite proportions

Dalton's mistaken belief about atoms

1808

John Dalton applied the term "atom" to the basic units of mass of the chemical elements under the mistaken belief that chemical atoms are the fundamental particles in nature; it was another century before scientists realized that Dalton's so-called atoms have an underlying structure of their own.

Flaw in Dalton's theory corrected by Avogadro

1811

The flaw in Dalton's theory was corrected in principle in 1811 by Amedeo Avogadro, who concluded that atoms combine in simple whole-number ratios and proposed that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.

Image source: Amedeo Avogadro

Flaw in Dalton's theory corrected by Avogadro

Periodic table and molecular architecture discovered

1875 - 1899

The anti-atomist positions of the equivalentists and energeticists were eventually quashed by two important advancements that happened later in the 19th century: the development of the periodic table and the discovery that molecules have an internal architecture that determines their properties.

Advances in Understanding

Molecular motion explains pressure and heat

1738

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.

Image source: Daniel Bernoulli

Molecular motion explains pressure and heat

Discovery of isomers

1830

In 1830, Jöns Jacob Berzelius introduced the term isomerism to describe the phenomenon of compounds with the same composition but different arrangements of their atoms.

Hypothesis of different arrangements of isomers

1860

In 1860, Louis Pasteur hypothesized that the molecules of isomers might have the same composition but different arrangements of their atoms in three dimensions.

Image source: Isomer

Hypothesis of different arrangements of isomers

Statistical mechanics applied to atomic theory

1860

In 1860, James Clerk Maxwell, a vocal proponent of atomism, was the first to use statistical mechanics in physics to describe the behavior of gases and the motion of particles.

Image source: James Clerk Maxwell

Statistical mechanics applied to atomic theory

Tetrahedral arrangement proposed for carbon bonds

1874

In 1874, Jacobus Henricus van 't Hoff proposed that the carbon atom forms bonds to other atoms in a tetrahedral arrangement, which explained the existence of optical isomerism.

Image source: Jacobus Henricus van 't Hoff

Tetrahedral arrangement proposed for carbon bonds

Discovery of electrons

1897

Atoms were thought to be the smallest possible division of matter until 1897 when J. J. Thomson discovered electrons, which he called "corpuscles" or "electrons".

Image source: J. J. Thomson

Discovery of electrons

Planetary atom models proposed

1903 - 1904

In 1903, Hantaro Nagaoka challenged Thomson's plum pudding model with a "Saturnian" model, in which electrons orbit a massive positive center like the rings of Saturn.

Brownian motion explained by molecular motion

1905

In 1905, Albert Einstein theorized that the random motion of particles suspended in a fluid, known as Brownian motion, was caused by the continuous motion of the fluid's molecules.

Image source: Brownian motion

Brownian motion explained by molecular motion

Validation of Einstein's Brownian motion theory

1908

Einstein's model of Brownian motion was validated experimentally in 1908 by French physicist Jean Perrin, who used Einstein's equations to determine the size of atoms.

Image source: Jean Baptiste Perrin

Validation of Einstein's Brownian motion theory

Rutherford's discovery of atomic nucleus

1911

Thomson's plum pudding model was overturned in 1911 by Ernest Rutherford, who discovered that most of the mass and positive charge of an atom is concentrated in a very small fraction of its volume, which he assumed to be at the very center.

Image source: Ernest Rutherford

Rutherford's discovery of atomic nucleus

Quantum Revolution

Quantum atomic models developed

1910 - 1912

This led to a series of quantum atomic models such as the quantum model of Arthur Erich Haas in 1910 and the 1912 John William Nicholson quantum atomic model that quantized angular momentum as h/2π.

Bohr's atomic model with quantized orbits

1913

In 1913, Niels Bohr incorporated the idea of quantized energy levels 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.

Image source: Bohr model

Bohr's atomic model with quantized orbits

Discovery of isotopes

1913

While experimenting with the products of radioactive decay, in 1913 radiochemist Frederick Soddy discovered that there appeared to be more than one variety of some elements.

Image source: Isotope

Discovery of isotopes

Sommerfeld's model with elliptical orbits

1916

In 1916, Arnold Sommerfeld added elliptical orbits to Bohr's model to explain the extra emission lines observed in atomic spectra.

Image source: Arnold Sommerfeld

Sommerfeld's model with elliptical orbits

Wave-particle duality proposed by de Broglie

1924

In 1924, Louis de Broglie proposed that all moving particles, including subatomic particles like electrons, exhibit wave-like behavior.

Image source: Louis de Broglie

Wave-particle duality proposed by de Broglie

Schrödinger's wave function equation

1926

Schrödinger's equation, published in 1926, describes an electron as a wave function instead of as a point particle, providing a mathematical framework for quantum mechanics.

Image source: Schrödinger equation

Schrödinger's wave function equation

Heisenberg's uncertainty principle

1927

Werner Heisenberg first published a version of the uncertainty principle in 1927, which states that the more precisely one measures the position of a particle, the less precisely one can measure its momentum, and vice versa.

Image source: Uncertainty principle

Heisenberg's uncertainty principle

Discovery of neutrons

1932

The nature of differing atomic masses was later explained by the discovery of neutrons in 1932: all atoms of the same element contain the same number of protons, while different isotopes have different numbers of neutrons.

Discovery of the neutron by Chadwick

1932

In 1932, James Chadwick exposed various elements to a mysterious radiation and deduced the existence of electrically neutral particles with a mass similar to that of a proton, which were later named neutrons.

Image source: James Chadwick

Discovery of the neutron by Chadwick

Key Facts

  1. John Dalton proposed the first modern atomic theory in 1803.
  2. J.J. Thomson discovered the electron in 1897.
  3. Ernest Rutherford's gold foil experiment in 1911 led to the discovery of the atomic nucleus.
  4. Niels Bohr developed the planetary model of the atom in 1913.
  5. The development of quantum mechanics in the 1920s revolutionized our understanding of atomic structure.

Source

This Atomic Theory timeline was generated with the help of AI, using information found on the internet.

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