Atomic Theory

Democritus Came up with idea of the atom. Greek philosopher - 470-380 B.C. Came up with idea of the atom. Used logical thinking - No experimentation. Atomos = Greek for 'indivisible’. Everything in the universe made up of atoms – microscopic, indestructible, solid spheres.

John Dalton Father of the Atom First Atomic Theory stated: Each element composed of atoms. Atoms of an element are identical Different element’s atoms have different characteristics. Atoms combine in whole # ratios to form compounds. Chemical reactions occur due to separating and rejoining or rearranging of atoms.

J. J. Thomson Identified the electron and proton. British scientist (1856-1940) Identified the electron and proton. Discovered electrons using the cathode ray tube and magnets. http://highered.mcgraw-hill.com/sites/0072512644/student_view0/chapter2/animations_center.html# Concluded that the electron was negatively charged and the proton positively charged. “Plum Pudding” model: Positive sphere with negative electrons embedded in it. (Like chocolate chip cookie dough)

Ernest Rutherford Discovered the nucleus. Experimented using alpha radiation and gold foil. http://highered.mcgraw-hill.com/sites/0072512644/student_view0/chapter2/animations_center.html# Nucleus is a dense, positive core in the center of the atom Electrons move around the nucleus. Atom is mostly empty space. nucleus

James Chadwick Identified the neutron. Neutron has no charge. Found in nucleus. Has a mass equal to a proton. Neutron served as “nuclear cement” by separating the protons and accounted for missing mass of atom.

Neils Bohr Developed the Bohr Model of the atom. Bohr Model: Electrons move around the nucleus in fixed, circular orbitals that have a set amount of energy levels. Racetrack model

Erwin Schrödinger Inventor of the theory of quantum mechanics Described the electron as a wave function rather than as a particle Assigned 4 quantum numbers to each electron in an atom to describe it (s, p, d, f)

     Summary Greeks (Democritus) 500 BC matter was made of tiny particles 4 elements: earth, wind, fire, water John Dalton  (Father of the Atom)   early 1800's            matter is made of indivisible particles called atoms            all atoms of same element are alike J.J. Thomson   1897           discovered electron with negative charge; reasoned the existence of positive particle           plum pudding model Ernest Rutherford   1911           discovered nucleus containing positive particles           gold foil experiment Neils Bohr   1913           energy levels holding electrons           worked with Rutherford and Einstein Erwin Schrödinger   1926           Electrons in clouds           Quantum (wave) theory           Assigned a set of four quantum numbers to describe the location of an electron James Chadwick   1932           discovered neutron           neutron holds protons apart           explained mystery of mass and 'glue' to hold nucleus together