Atomic Orbital Filling Order and Electron Configurations AP Chemistry

There are 3 main rules for filling atomic orbitals 1. Aufbau principle - Electrons get filled in order from lowest to highest energy levels. Each atom has seven possible energy levels (cleverly labeled 1 through 7). One is the lowest, seven is the highest. They go by period (rows) in the periodic table. Each atom has seven possible energy levels (cleverly labeled 1 through 7). One is the lowest, seven is the highest. They go by period (rows) in the periodic table. The possible number of electrons for an energy level is found by using the equation 2n 2 (where n = an energy level, 1-7). The possible number of electrons for an energy level is found by using the equation 2n 2 (where n = an energy level, 1-7).

Each energy level is further divided into sublevels. There are four basic types of sublevels which are arranged by groups. Each energy level is further divided into sublevels. There are four basic types of sublevels which are arranged by groups. s -- The “s” sublevel has one orbital. s -- The “s” sublevel has one orbital. p -- The “p” sublevel has three orbitals. p -- The “p” sublevel has three orbitals. d -- The “d” has 5 orbitals. d -- The “d” has 5 orbitals. f -- The “f” sublevel has 7 orbitals. f -- The “f” sublevel has 7 orbitals.

Due to energy levels becoming closer together as “n” increases, there is some overlap of the sublevels.

Increasing energy 1s 2s 3s 4s 5s 6s 7s 2p 3p 4p 5p 6p 3d 4d 5d 7p 6d 4f 5f Orbital diagram Aufbau is German for “building up” We must follow this orbital energy diagram! Notice that the 4s orbital will fill before the 3d because it is lower in energy!

2. Pauli exclusion principle - Only two electrons can fit in each orbital, one with an “up” spin, the other with a “down” spin - Only two electrons can fit in each orbital, one with an “up” spin, the other with a “down” spin -This means that each “s” has 2 electrons, “p” has 6 (3 orbitals with 2 e- each), “d” has 10, and “f” has 14. -This means that each “s” has 2 electrons, “p” has 6 (3 orbitals with 2 e- each), “d” has 10, and “f” has 14. To show the different direction of spin, a pair in the same orbital is written as:

3. Hund’s rule When filling a sublevel with multiple orbitals (p, d, or f), each orbital gets one electron (the “up” spin) before any get two. When filling a sublevel with multiple orbitals (p, d, or f), each orbital gets one electron (the “up” spin) before any get two.

Orbital Diagram for Sodium 1s 2s 2p 3s 3p 4s Sodium has 11 electrons Energy

Orbital Diagram for Bromine Bromine has 35 electrons Electron Configuration is 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 5

Electron Configuration An atom’s electron configuration is the position of its electrons around the nucleus. It reflects the orbital filling diagram. An atom’s electron configuration is the position of its electrons around the nucleus. It reflects the orbital filling diagram. The electron configuration of Sodium is 1s 2 2s 2 2p 6 3s 1 The electron configuration of Sodium is 1s 2 2s 2 2p 6 3s 1 -- This goes in order on the periodic table from the first level to last electron the atom has. -- This goes in order on the periodic table from the first level to last electron the atom has. The number in front of the letter tells the current energy level (1-7). The number in front of the letter tells the current energy level (1-7). The letter tells you the sublevel. The superscript after the letter tells you how many electrons have been filled in that sublevel. The letter tells you the sublevel. The superscript after the letter tells you how many electrons have been filled in that sublevel.

Writing Electron Configuration of Sodium 1s 2s 2p 3s 3p 4s Energy 1s 2 2s 2 2p 6 3s 1

Increasing energy 1s 2s 3s 4s 5s 6s 7s 2p 3p 4p 5p 6p 3d 4d 5d 7p 6d 4f 5f

Valence electrons Valence electrons are electrons located in the outermost energy level. Valence electrons are electrons located in the outermost energy level. They are located only in the s and p sublevels They are located only in the s and p sublevels These electrons are involved in chemical bonding. These electrons are involved in chemical bonding.

Electron Configurations An element’s electron configuration shows how many valence electrons it has. An element’s electron configuration shows how many valence electrons it has. Example: Example: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 4 Valence electrons = 6

Practice How many valence electrons do the following elements have? How many valence electrons do the following elements have? 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 1s 2 2s 2 2p 6 3s 2 3p 2 1s 2 2s 2 2p 6 3s 2 3p 2 1s 2 2s 2 1s 2 2s 2 8 valence electrons 4 Valence Electrons 2 valence electrons

Shorthand Configuration Shorthand Configuration S 16e - Valence Electrons Core Electrons S16e - [Ne] 3s 2 3p 4 1s 2 2s 2 2p 6 3s 2 3p 4 Noble Gas Shorthand Electron Configurations Longhand Configuration Longhand Configuration

Noble Gas Shorthand Configuration Shorthand Configuration Shorthand Configuration –Core e - : Go up one row and over to the Noble Gas. –Valence e - : On the next row, fill in the # of e - in each sublevel.

[Ar]4s 2 3d 10 4p 2 Noble Gas Shorthand Notation Example - Germanium Example - Germanium

Paramagnetic vs. Diamagnetic Depends on presence of unpaired electrons in an atom Diamagnetic – Atom has all paired electrons. It will be repelled from an induced magnetic field. Paramagnetic – Atom has unpaired electrons. It will be attracted into an induced magnetic field.