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400 BCE
Democritus's Atomic Model
The atomic model of Democritus stated that matter consisted of atoms and an empty space. He also stated that the atoms are indestructible and unchangeable. Also, tht they are homogeneous, meaning that they have no internal structure.His atomic model was solid, and stated all atoms differ in size, shape, mass, position and arrangement, with a void exists between them. He said that if you took a stone and cut it in half, each piece would have the same properties as the original stone. -
Billiard Ball Model (Dalton´s Atomic Model)
He said that all elements were composed of atoms, and it is impossible to divide or destroy an atom. He also stated that all the atoms of the same element are alike, and of other elements are diffetent. He said that toms of different elements combine to form a compound.
He used patterns within the circles to distinguish the different elements. Dalton carried out experiments, using the law of multiple proportions, and completed the table of atomic weights. -
Plum Pudding Model (J.J. Thomson)
As each atom was a sphere filled with a positively charged fluid, known as the “pudding”. Scattered in this fluid were negatively charged electrons, these were the “plums” in the pudding. Thomson suggested that the positive fluid held the negatively charged electrons in the atom because of its electrical forces. -
Planetary Model (Ernest Rutherford)
He proposed that atoms consisted of a small dense center filled with positive charges. He then said that negatively charged electrons were scattered surrounding this dense, positively charged center. Rutherford performed a series of experiments with radioactive alpha particles. He fired alpha particles at solid objects. He found that while most of the alpha particles passed through the object, a small number of alpha particles bounced straight back like a tennis ball hitting a wall. -
Energy Level Model (Neils Bohr)
He stated they moved in fixed, circular orbits around the nucleus, these called electron shells. Electrons orbit the nucleus at set distances. When an electron changes orbits, it does so in a sudden quantum leap. The energy difference between the initial and final orbit is emitted by the atom in bundles of electromagnetic radiation called photons. This model was based on his observations of the atomic emissions spectrum of the hydrogen atom. -
Quantum Mechanical Model (Erwin Schrödinger)
Schrodinger discovered that electrons don't move in orbits (or in a set path at all). He theorizes electrons move in waves, and they have no exact location. Schrodinger discovered that electrons don't move in orbits (or in a set path at all). He theorizes electrons move in waves, and they have no exact location.
