Arrangement of the Atom

Principle Quantum Number The Principle Quantum Number, symbolized by n, indicates the main energy level occupied by the electron. Values of n are positive intergers only and start with the number 1. The level n =1 has the lowest energy. increase in energy

Sublevels and Their Relative Energies There are four known sublevels , s, p, d and f. Energy level n = 1 has one sublevel, energy level n = 2 has two sublevels, energy level n = 3 has three sublevels, etc. The sublevels indicate the shape of the orbital.

Relative Energy of Orbitals Each sublevel is broken up into orbitals. An orbital is a three-dimensional region around the nucleus that indicates the probable location of an electron. The s sublevel has 1 orbital, the p sublevel has 3 orbitals, the d sublevel has 5 orbitals, and the f sublevel has 7 orbitals.

Filling Orbitals With Electrons There are Three Guidelines to Follow When Filling Orbitals with Electrons. Aufbau’s Principle Pauli’s Exclusion Principle Hund’s Rule

Aufbau’s Principle Aufbau’s Principle: An electron occupies the lowest-energy orbital that can receive it. By looking at the diagram you can see that the 1s orbital is lowest in energy. Therefore, electrons would fill the 1s orbital first before filling the 2s orbital. Fills third Fills second Fills first

Pauli’s Exclusion Principle Pauli’s Exclusion Principle: No two electrons in the same atom can have the same set of four quantum numbers. This implies that there is a maximum of 2 electrons in each orbital and those 2 electrons must have different a different spin. Electrons are represented by arrows and two arrows in the same orbital face different directions to indicate different spin. Now this level is full. Where do the next electrons go?

Hund’s Rule Hund’s Rule: Orbitals of equal energy are each occupied by one electron before any orbital is occupied by a second electron, and all electrons in singly occupied orbitals must have the same spin.

Orbital Diagrams of Elements

Electron Configurations The letter s represents the sublevel. These numbers represent the number of electrons in each sublevel. 1s22s1 These numbers represent the principle energy level where the electrons can be found.

Electron Configurations

Reading the Periodic Table The s, p, d, and f Blocks

Reading the Periodic Table

Noble Gas Configurations Some electron configurations can be very long such as the electron configuration for iodine 1s22s22p63s23p64s23d104p65s24d105p5. Noble gas configurations can be used to shorted the electron configurations. To Determine Your Noble Gas Configuration: 1. Find your element on the periodic table. 2. Find the noble gas that appears before your element. This noble gas represents the inner electrons. See the figure below for finding P and its previous noble gas, Ne. 3. Write the noble gas configuration in the following format. [noble gas symbol] outer electron configuration For Phosporous: [Ne]3s23p3 For Iodine: [Kr] 5s24d105p5