Atomic Models and Theory Timeline

• Democritus- He claimed that matter was made of small, hard particles, that he called "atoms".
• Dalton- He created the very first atomic theory.
• Thomson- He showed that the atom was made of even smaller things.
• Rutherford- He discovered protons and nucleus.
• Bhor- He improved on Rutherford's model.
• Chadwick- He discover neutrons.
• Modern- Work done since 1920 has changed the model
• The electrons are spread out around the edge of the atom. They orbit the nucleus in layers called Shells.
• The protons and neutrons exist in a dense core at the center of the atom. This is called Nucleus.
• The two properties of subatomic particles are mass and electrical charge.
• Louie De Broglie- He proposed that the electron could also be thought as wave.
• Erwin Schrodinger- used the wave idea to develop a mathematical equation to describe the hydrogen atom.
• Werner Karl Heisenberg- discovered that for a very small particle like the electron, its location cannot be exactly known, and how it is moving.
• Uncertainty Principle- you can't locate the exact position of an electron at any given time (too small, too fast)
• Quantum Mechanical Model- Also gives information about the energy of the electron and describes the region of space around the nucleus as consisting of shells.
• Aufbau Principle: electrons enter orbitals of lowest energy first.
• The name consists of three quantum numbers: Principal quantum number, Angular momentum quantum number, and magnetic quantum number.
• Pauli exclusion Principle- An atomic orbital can describe at most two electrons.
• Hand's rule- when electrons occupy orbitals of the same energy, electrons will enter empty orbitals first.
• The three specific principles are the hand's rule, Aufbau principle, Pauli exclusion principle.
• quantum mechanics- may be used to determine the arrangement of the electrons within an atom if three specific principles are applied.
• principle quantum number- distribution of all electrons in an atom.
• magnetic quantum number- It describes the orientation of the orbital sound around the nucleus.
• Angular momentum quantum number- describe the shape of the orbitals.