Events
Antoine Lavoisier:
Discovered the law of conservation of mass which states that mass can neither be created nor destroyed in a chemical reaction;
Mass is conserved in a chemical reaction;
The total mass of the products of a chemical reaction is always the same as the total mass of the starting materials consumed in the reactionPlum Pudding Model:
Created by J.J Thomson;
Negative electrons represent raisins, embedded in the dough (a positively charged substrate);
The atom is composed of electrons surrounded by a soup of positive charge to balance the electrons' negative chargesBohr Planetary Model:
Created by Niels Bohr;
Depicts the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus;
Electrons orbit the nucleus in orbits that have a set size and energy;
The energy of the orbit is related to its size. The lowest energy is found in the smallest orbit;
Radiation is absorbed or emitted when an electron moves from one orbit to anotherDemocritus created the Atomic Theory: Everything is composed of “atoms”, which are physically, but not geometrically, indivisible;
Between atoms, there lies empty space;
Atoms are indestructible;
Atoms have always been, and always will be, in motion;
There are an infinite number of atoms, and kinds of atoms, which differ in shape, and size.J.J. Thomson:
Discovered the electron by discovering that cathode rays are negatively charged;
Created the plum pudding modelJohn Dalton discovered All matter is made of atoms;
Atoms are indivisible and indestructible;
All atoms of a given element are identical in mass and properties;
Compounds are formed by a combination of two or more different kinds of atoms;
A chemical reaction is a rearrangement of atomsGold Foil Experiment:
Aimed alpha particles at gold foil and recorded their location as they passed through the foil-> a small number of particles ricocheted back;
Rutherford concluded the atom consisted of a small, dense, positively charged nucleus in the center of the atom with negatively charged electrons surrounding it.Cathode Ray Tube Experiment:
Done by J.J Thomson;
Found that many different metals release cathode rays, and that the rays were made of electrons, very small negatively charged particles;
He constructed a cathode ray tube, with a fluorescent coating at one end and a vacuum. Halfway down the tube were two electric plates, producing a positive and negative cathode.
The rays were deflected by the electric charge, proving that the rays were made up of charged particles carrying a negative chargeRobert Millikan:
Performed the oil drop experiment;
Measured the charge of an electron;
Offered convincing proof that electric charge exists in basic natural unitsJames Chadwick:
Played a vital role in the atomic theory, as he discovered the Neutron in atom;
Neutrons are located in the center of an atom, in the nucleus along with the protons. They have neither a positive nor negative charge, but contribute the the atomic weight with the same effect as a proton.Erwin Schrodinger :
Invented the quantum mechanical model of the atom, which describes the likelihood of finding an electron in a certain position.Niels Bohr:
Proposed a theory for the hydrogen atom based on quantum theory that energy is transferred only in certain well defined quantities;
Electrons should move around the nucleus but only in prescribed orbits. When jumping from one orbit to another with lower energy, a light quantum is emitted.Oil Drop Experiment:
Performed by Robert A. Millikan and Harvey Fletcher;
Observing tiny electrically charged droplets of oil located between two parallel metal surfaces, forming the plates of a capacitor to measure the electric charge of an electron;
Offered convincing proof that electric charge exists in basic natural unitsLaw of Conservation of mass:
Created by Antoine Lavoisier;
States that mass can neither be created nor destroyed in a chemical reaction.Dalton's atomic theory:
Created by John Dalton;
Proposed the theory that all matter was composed of atoms, indivisible and indestructible building blocks;
While all atoms of an element were identical, different elements had atoms of differing size and mass.Rutherford Model:
Created by Ernest Rutherford;
Proved J.J Thomson’s plum pudding model incorrect;
Proposed that an atom is composed of empty space mostly with electrons orbiting in a set, predictable paths around fixed, positively charged nucleusElectron Cloud Model:
The electron cloud model was developed by Erwin Schrödinger;
It consisted of a dense nucleus surrounded by a cloud of electrons at various levels in orbitals;
Where the cloud is most dense, the probability of finding the electron is greatest, and the electron is less likely to be in a less dense area of the cloudErnest Rutherford:
Was the first to discover that atoms have a small charged nucleus surrounded by largely empty space, and are circled by tiny electrons, which became known as the Rutherford model (or planetary model) of the atom.
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