Electron Configuration

The way electrons are arranged around the nucleus Electrons are organized around the nucleus so that they are at the lowest energy level The configuration of electrons determines the properties of matter

Valence electrons are the outermost electrons move between atoms in a chemical reaction to form or break bonds Elements in the same family have the same number of valence electrons and so they have similar properties So, we don’t really care about all the electrons but we need to know how many electrons are in the outermost level

Principal Quantum Number Indicates main energy level n = 1, 2, 3, 4… Each main energy level has sub-levels N is equal to the row number of the element

The principle quantum number, n, also determines the number of sublevels within the principle energy level. For the main group elements, Energy sublevels go in the order s, p, d

Orbitals in Sublevels The number of orbitals is 1 in the first sublevel and increases by 2 each additional sublevel. There are 2 electrons in each sublevel. For the main group elements: Sublevel # Orbitals # electrons s12 p36 d510

Blocks in the Periodic Table

Aufbau Principle Electrons occupy orbitals of lower energy first. This matches the left to right reading of the periodic table.

Notations of Electron Configurations Standard Shorthand

Standard Notation 1. Find the element 2. Write the number and sublevel letters of blocks up to and including the element The number is row number for S and P, row number minus 1 for D Columns 1 & 2 are “S”, Columns are “P”, Columns are “D” 3. Write the number of elements in the block as a superscript in blocks before the element 4. Count how many into the last block the element is and write that number as the superscript on the last sublevel

Standard Notation of Fluorine Main Energy Level Numbers 1, 2, 2 Sublevels Number of electrons in the sub level 2,2,5 1s 2 2s 2 2p Row 1 Row 2 S P S

Try these… Iron 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 6 Tin 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 2 Calcium 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2

Shorthand Notation Use the last noble gas that is located in the periodic table right before the element. Write the symbol of the noble gas in brackets. Write the remaining configuration after the brackets. Ex: Fluorine: [He] 2s 2 2p 5

Try these Again… Iron [Ar] 4s 2 3d 6 Tin [Kr] 5s 2 4d 10 5p 2 Calcium [Ar] 4s 2

Recap: Why do we care so much about electrons? Do we care about all of the electrons equally? Do you think the shorthand version works as well as the long-form?