Chemistry Scientists with the Discovery of Atomic Structure

Democritus

greek philosopher, about 400 BC, Proposed that all matter is made up of tiny, invisible particles called atoms

Robert Boyle

regarded as the first modern chemist. defined the element as a substance that cannot be broken down into two or more simpler substances by chemical means

Joseph Priestley

english educated, 1794 discovered oxygen

Antoine Lavoisier

French Chemist, proposed the law of conservation of mass. Father of Modern Chemistry

Joseph Proust

french chemist. 1799 Proposed Law of Definite Proportions: a given compound always contains the same elements in the same proportions by mass

John Dalton

English school teacher in 1803, proposed the Atomic Theory of Matter

Benjamin Franklin

American philosopher. Flew a kite attached to a key in a thunderstorm to study electricity. Concluded there are two kinds of electrical charges, positive (+) and negative (-)

Michael Faraday

English chemist. 1839 suggested that the structure of atoms is related to electricity

J.J. Thomson

English physicist. He concluded that the cathode ray was composed of negatively charged particles that were emitted from the cathode. In 1897, he named the particles electrons and determined the ratio of the electron's charge to its mass. Proposed the plum-putting model of the atom

Robert Millikan

American physicist. Oil drop experiment. He determined the charge of a single electron was 1.60 x 10^-19 C and so was able to determined the mass of the electron was 1/2000 of the mass of the smallest atom, the hydrogen atom

Henri Becquerel

French physicist. 1896, discovered radioactivity

Ernest Rutherford

New Zealand Chemist. worked in Britain at Cambridge University: Gold Foil Experiment. Concluded that the atom is mostly empty space with a very tiny, positively charged, dense center he called the nucleus. He proposed that the negatively charged electrons orbited around the nucleus. "It was quite the most incredible event that has ever happened to me in my life. It was almost as if you fired a 15-inch shell into a piece of tissue paper and it came back and hit you."

Niels Bohr

Danish physicist, solved the puzzle of the hydrogen-atom spectrum in 1913. Proposed a model of the hydrogen atom that linked the atom's electron with photon emission. According to the _____ model, electrons travel around the nucleus in fixed orbits, called the Planetary Model.

Henry Moseley

British chemist and physicist. Named the individual positive charged proton. Establish that the atomic number of the atom defines the identity of the element (equals the # of protons)

James Chadwick

British physicist. In 1932 discovered the existence of neutrons or neutrally charged particles in the nucleus. Neutrons are slightly heavier than protons, and found in the nucleus

Max Planck

German physicist. While studying the emission of light by hot objects, he proposed that a hot object does not emit electromagnetic energy continuously, as would be expected if energy emitted wee in the form of waves. suggested that objects emit energy in small, specific amounts called quanta. Planck proposed the relationship between a quantum of energy and the frequency of radiation. E = hv (______ constant : h = 6.626 x 10^-34 J x s)

Albert Einstein

German physicist. Einstein expanded on Planck's work and introduced the radical idea that electromagnetic radiation has dual wave-particle nature. Light exhibits wave-like properties, but can be though of as a stream of particles. Each particle of light carries a quantum of energy. Einstein called these particles photons.

Louis de Broglie

French Scientist, suggested that electrons be considered waves confined to the space around an atomic nucleus. Electron waves could exist only at specific frequencies.

Werner Heisenberg

German physicist. developed the Heisen berg Uncertainty Principle. It states that it is impossible to determine simultaneously both the position and velocity of an electron or any other particle. Although it was difficult for scientists to accept this fact at the time, it has proven to be one of the fundamental principles of our present understanding of light and matter

Erwin Schrodinger

in 1926, Austrian physicist, used the hypothesis that electrons have a dual wave-particle nature to develop an equation that treated electrons as waves. Based on the works of Heisenberg and Schrodinger quantum theory was developed that would give only the probability of finding an electron at a given place around the nucleus. Thus electrons do not travel around the nucleus in neat paths proposed by Bohr. Instead, they exist in certain regions called orbitals

Quantum theory

describes mathematically the wave properties of electrons