Electron Configuration

If you were absent on Friday, you need to do the “Periodic trends Quiz on Moodle” Review on Periodic Trends : (do in composition book & update ToC) 1. As you move down the periodic table the atomic radius tends to increase/decrease (circle one). 2. As you move across the periodic table the atomic radius tends to increase/decrease (circle one). 3. Re-write the following in increasing order according to atomic radius: Mg, Be, Ca __________________ 4. As you move down the periodic table the ionization & electronegativity energy tends to increase/decrease (circle one). 5. As you move across the periodic table the ionization & electronegativity energy tends to increase/decrease (circle one). 6. Re-write the following in increasing order according to ionization & electronegativity energy: B, Al, In __________________

10/16 Electron Configuration Where are all the other electrons located in an element? If Calcium has atomic # 20, where are those electrons at in the element? We know there are ____ valence e- & there are ___ orbitals around Ca but what about the other ___ electrons that exist in Ca?

Valence electrons 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 n Indicates main energy level (period #) n = 1, 2, 3, 4… Each principal energy level has sub-levels that may include: s,p,d,or f s can holds max of 2 e- p can hold max of 6 e- d can hold max of 10 e- f can hold max of 14 e-

Electron Configuration & using the periodic table: Electron configuration is the arrangement of electrons on various orbitals around the nucleus to be the most stable.

Write on your blank periodic table the yellow boxes for where s, p, d, f sections are located. The # is the period they are located

Blocks in the Periodic Table

Use the periodic table or you can use the Aufbau Diagram to write e- configuration:

9 8 7 6 4 3

Standard Notation of Fluorine Number of electrons in the sub level 2,2,5 1s2 2s2 2p5 Main Energy Level Numbers 1, 2, 2 Sublevels S S P 9 8 7 6 4 3 Row 1 Row 2 Row 2

Standard Notation Find the element 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 10-12 are “P”, Columns 13-18 are “D” Write the number of elements in the block as a superscript in blocks before the element Count how many into the last block the element is and write that number as the superscript on the last sublevel

Try these… 4. Iron 1. Nitrogen 1s2 2s2 2p3 2. Potassium 3. Calcium 1s2 2s2 2p6 3s2 3p6 4s1 3. Calcium 1s2 2s2 2p6 3s2 3p6 4s2 4. Iron 1s2 2s2 2p6 3s2 3p6 4s2 2 3d6

10/17 What elements are these? How many valence e- are in each? Which will gain valence e- to reach 8 or give up valence e- & satisfy the octet rule ? 1. 1s22s22p5 2. 1s22s22p63s23p1 3. 1s22s22p63s23p64s23d7 4.1s22s22p63s23p64s23d104p65s1 5. [Ar] 4s23d9 6. [Xe] 6s24f145d4

Three Rules to follow in doing electron configuration: Aufbau principle – in which e- occupy orbitals of lowest energy first (is why 4s has 2 e- before 3d gets any electrons from the transition metals in period 4) & use the diagonal “Aufbau chart” to do this (but we will follow the periodic table to do same thing) Pauli exclusion principle – refers to why 2 e- can be close on the same orbital due to opposite spins to allow 2 negative electrons to be attracted and close to each other Hund’s rule – within each orbital the s, p, d and f sublevels must have at least one electron in each before a second electron of opposite spin is added for when we write the “e- spin configuration”

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

Notations of Electron Configurations Why is it important to understand where electrons are somewhat located within an element? How can so many electrons be in an element, like 38 e- in Strontium? Write e- configuration for Sr. How do e- “pair up?’

Pauli exclusion principle – refers to why 2 e- can be close on the same orbital due to opposite spins to allow 2 negative electrons to be attracted and close to each other

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] 2s2 2p5

Try these in shorthand notation: 1) Iron [Ar] 4s2 3d6 2) Tin [Kr] 5s2 4d10 5p2 3) Calcium [Ar] 4s2

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?