Scientists (History of the Atom)

JJ Thomson's Model of the Atom

"plum pudding" model, with electrons spread out and positive charge like pudding throughout

Chronological Order

Democritus, John Dalton, JJ Thomson, Robert Millikan, Ernest Rutherford, Niels Bohr & James Chadwick

Robert Millikan's Discovery

Determined the mass of the electron

James Chadwick's Discovery

Discovered the neutron

Ernest Rutherford's Discovery

Discovered the proton, and created the planetary model of the atom

John Dalton's Discovery

Elements are made of extremely small particles called atoms. Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties. Atoms cannot be subdivided, created, or destroyed.

Niels Bohr's Discovery

Found electron shells/orbitals, model of atom

Name and Explanation of Niels Bohr's Experiment

He proposed that any electron can be found on specific circular path called the orbitals. It states that the energy of an electron is proportional to the distance away from the nucleus it is. The farther away the electron orbital is away from the nucleus the more energy it has. There are certain amounts of orbitals with certain energy levels meaning that the orbitals are quantized.

Name and Explanation of John Dalton's Experiment

He studied meteorology, created daltons law of partial pressure: in a mixture of non-reacting gases, the total pressure exerted is equal to the sum of the partial pressures of the individual gases.

Name and Explanation of James Chadwick's Experiment

Put beryllium in vacuum chamber with polonium Put target in between rays Atoms that were electronically charged went into gas chamber (detector) Atoms went through and were ionized Measured current through electrode Bombarded boron with alpha particles Boron emitted neutral rays Hydrogen target placed and protons flew out Conservation of momentum and energy Chadwick found mass as 1.0067 times proton

JJ Thomson's Discovery

discovered the electron, or negative charge in the atom

Democritus' Discovery

discovered the idea of the atom

Name and Explanation of Ernest Rutherford's Experiment

gold foil experiment, Rutherford aimed a beam of alpha particles at a piece of gold foil. A zinc sulfide screen was placed behind the foil as a backdrop to see the alpha particles on. Above this screen was a microscope that allowed one of the experimenters to observe. Once the setup was done, they fired the beam of alpha particles through the piece of foil. Majority of alpha particles passed straight through the gold foil, a small hand full of particles that deflected slightly from the straight path by about one or two degrees,and 1 in 20,000 particles deflected almost 90 degrees from the beam. Or when an occasional particle even fired right back at the experimenter. Since the gold had very spread apart atoms, this shows only a positive charge would bounce back, finding the proton.

James Chadwick's Model of the Atom

modern day model of the atom

Niels Bohr's Model of the Atom

modern model, orbitals, no neutron yet

Name and Explanation of Democritus' Experiment

no experiment, assumption

Name and Explanation of Robert Millikan's Experiment

oil drop experiment, Millikan placed negatively charged droplets of oil in between charged metal plates. He adjusted the voltage on the plates to see the affect it had on the speed of the falling oil. From his results, he was able to calculate the charge of an electron when he found that the charge of each droplet was a multiple of 1.60 x 10-19 coulomb, and with the help of Thomson's previous research, Millikan was able to find the mass of an electron

Name and Explanation of JJ Thomson's Experiment

passing electric current through a sealed low pressure container. The ends of the glass tubes were fitted with metals disks called electrodes. The electrodes were connected to a battery. One electrode, the anode, became positively charged and the other electrode, the cathode, became negatively charged. This caused a glowing beam to form, also known as a cathode ray which was flowed from the cathode to the anode. Thomson's conclusion was that the glowing light (cathode ray) was caused by a stream of negatively charged particles moving incredibly fast.

Robert Millikan's Model of the Atom

plum pudding

Ernest Rutherford's Model of the Atom

protons in the center (nucleus), no neutrons yet, electrons around in ring-type setup

Democritus's Model of the Atom

tiny sphere

John Dalton's Model of the Atom

tiny sphere