1. Atomic Models and Electron Configuration

2. The history of the atomic model Democritus Created in 400 BC Atoms are indivisible and indestructible Not scientifically proven Dalton Each element was composed of identical atoms. Atoms of different elements can physically or chemically combine in simple whole number compounds. Atoms of one element can never be changed into another. Chemical reactions occur when atoms are separated, joined, or rearranged

3. Thomson Discovered the electron Created the first model with subatomic particles Created the plum pudding model Rutherford Performed the gold foil experiment Discovered the nucleus and the proton Electrons move around the nucleus

4. Bohr Model The electrons are found in specific circular paths called orbits around the nucleus Each orbit is at a fixed energy level Electrons can gain or lose a quantum of energy to move up or down the orbits This model is the easiest to use when visualizing the atom but is not correct.

5. The Quantum Mechanical Model Was developed by Erwin Schrodinger The energy of electrons is restricted to certain values The electrons do not have specific paths around the nucleus Instead an electron’s location is described as a probability

6. Atomic Orbitals Solving Schrodinger’s equations led to atomic orbitals An atomic orbital is a region of space around the nucleus that has a high probability of having an electron in it. The energy levels of an electron are labeled by the principal quantum number n n represents the energy level and distance from the nucleus Each orbital can hold 2 electrons

7. Electrons in the Orbitals The maximum number of electrons than can occupy a principal energy level is given by the formula 2n 2 Energy Level nMaximum number of electrons 12 28 318 432

8. Sublevels There are 4 sublevels to each energy level that have specific shapes and can hold a certain number of electrons

13. Size of Orbitals The shape of an orbital is the same, but change size according to energy level 1s2s

14. Electron Configurations To write out an electron configuration for an element, write out the orbitals in order from lowest to highest and fill it with electrons. To write out the orbitals, follow the periodic table Orbitals must be filled in order of lowest to highest energy level