chemistry history

democritus

matter is made of tiny, invisible indescructible particles called atoms

aristotle

matter if made of four elements: fire, water, earth, and air

john dalton

published first atomic theory in 1803

daltons atomic theory

matter is composed of tiny fundamental and invisible particles called atoms

daltons atomic theory

atoms of the same elements are identical (isotopes)

daltons atomic theory

atoms of different elements are obviously different

daltons atomic theory

a compound is formed when 2 o rmore atoms combine in simple , whole number ratios

daltons atomic theory

atoms separate, rearrange, and recombine during a chemical reaction

JJ thomspon

conducted cathode ray tube experiments

JJ thomspon

a wheel inside the cathode ray tube spins, so cathode rays are made of particles not energy

JJ thomspon

cathode ray deflects away from the negative pole of a magnet, so particles that make up cathode ray are negative

JJ thomspon

calculated the mass of the cathode ray particles and found that they are about 2000 times smaller than the smallest known element, hydrogen

JJ thomspon

discovered the electron

JJ thomspon

concluded that since atoms are neutral there must be a positive charge in the atom tool.

JJ thomspon

came up with new model of the atom, called the palm pudding model: the atom is a positive solid with negative electrons scattered randomly throughout

ernest rutherford

conducted gold foil experiment

ernest rutherford

a beam of positive alpha particles is aimed at a thin sheet of gold fould, and a screen around the foil detects the path of the alpha particles

ernest rutherford

the expected result was if the plum pudding model is correct, all of the alpha particles would pass straight through the foil

ernest rutherford

result was most of the alpha particles passed straight through the gold foil. a few passed through with a slightly bent path, and about 1 in 20,000 particles bounded back towards the source of the particles

ernest rutherford

conclusion was that atom was mostly an empty space with a small, dense, positively charged area in the center, called the nucleus

neils bohr

proposed planetary model of the atom: electrons orbit the nucleus in circular energy levels like plants orbit around the sun

neils bohr

werner heisenberg

proposed the uncertainty principle in 1926

werner heisenberg

principle says the exact position of electrons cannot be known, so the best model for the location of the electrons is the electron cloud

erwin schrodinger

electrons have properties of both waves an d particles

erwin schrodinger

there are regions in the atom where there is high probability of finding electrons called orbitals

quantum mechanical model of the atom

the works of bohr, Heisenberg, Schrodinger, Einstein, and other physicists developed into this

james chadwick

discovered the neutron

modern atomic theory

matter is composed of tiny fundamental particles called atoms

modern atomic theory

an atom has two areas: a nucleus and an electron cloud

modern atomic theory

the nucleus is dense and positive, its made of positive protons and neutral neutrons

modern atomic theory

the electron cloud is a diffuse area outside other nucleus where negative electrons can be found

modern atomic theory

electrons exist in energy levels in the electron cloud aremos tlilely found in regions called orbitals

daltons atomic theory

democritus

aristotle

john dalton

jj tompson

ernest rutherford

niels bohr

werner heisenburg

erwin schrodinger

james chadwick