Presentation on theme: "Electron Configuration"— Presentation transcript:
1Electron Configuration History of Modern Atomic TheoryEnergy Levels and SublevelsThe Energy Levels
2History of Modern Atomic Theory Niels Bohr noticed that electrons could only gain certain amounts of energyThis implied that there were energy levels in the electron cloudElectrons could jump from one energy level to another, but could not exist between levels. The levels were still pictured as circular orbits.This model of the atom was called the Bohr model and agree with experimental data for hydrogen atoms. It failed to explain other atoms though.
3History of Modern Atomic Theory In the modern description of the electrons in atoms, the quantum mechanical model, the electron does not travel in a circular orbit, instead it exists somewhere within a region of space called an orbitalWe don’t know it exact position only the probability of finding itWe should no longer picture the electron as tiny particle whizzing around the nucleusThe propeller blade has the same probability of being anywhere in the blurry region, but you cannot tell its location at any instant. The electron cloud of an atom can be compared to a spinning airplane propeller.
4Energy Levels and Sublevels Remember that e- are what hold atoms together to form molecules. Understanding more about how they are arranged in the atom will help us better understand chemical reactionsThe electron cloud is divided into energy levelsTheoretically there are an infinite number of levels, but even the biggest atoms only use sevenThe energy levels closest to the nucleus are lower in energyElectrons always try to achieve the lowest energy state possible; this is called the Ground State.This tendency is known as the Aufbau Principle (which means to “Build up”)When we start to place electrons into energy levels we begin with the lowest levels and build our way up as needed.Each energy level contains one or more SublevelsThe first energy level has only one sublevel (called the s sublevel)The second energy level has two sublevels (called s and p sublevels)The third energy level has three sublevels (called s, p, and d sublevels)The fourth energy level has four sublevels (called s, p, d, and f sublevels)
5Energy Levels and Sublevels Each sublevel is divided into Orbitals which are 3 dimensional regions of space where a pair of e- is most likely to resideThe s sublevel (the first sublevel in every energy level) has one orbitalThe p sublevel (the second sublevel in energy levels 2-7) has three orbitalsThe d sublevel (the third sublevel in energy levels 3-7) has five orbitalsThe f sublevel (the forth sublevel in energy levels 4-7) has seven orbitalsEach orbital can house two electronsThe Apartment Building Analogy: You can think of the electron cloud as an apartment buildingThe energy levels are the same as the floorsThe sublevels are the same as the apartmentsThe orbitals are the same as a bunk bed for two peopleEach person represents an orbital
64 3 2 1 f s p s p s p s 4 sublevels 1+3+5+7=16 orbitals d4sp4 sublevels=16 orbitals= 32e-d33 sublevels1+3+5=9 orbitals= 18e-sp2 sublevels1+3=4 orbitals2 + 6 = 8e-21 sublevel1 orbital2e-s1
7Comprehension CheckKnowing that each orbital can hold 2 e-, how many electrons can the following sublevels hold?s sublevel1 orbital x 2 e- = 2 e-p sublevel3 orbitals x 2 e- = 6 e-d sublevel5 orbitals x 2 e- = 10 e-f sublevel7 orbitals x 2 e- = 14 e-
8Comprehension Check How many electrons can each energy level hold? 1st Energy Level2nd Energy Level3rd Energy Level4th Energy Level
9Answers to Comprehension Check How many electrons can each energy level hold?1st Energy Level2 (2)2nd Energy Level8 (2+6)3rd Energy Level18 (2+6+10)4th Energy Level32 ( )
10Energy Levels and sublevels Fill out the following table using what you know about electrons and energy levelsEnergy LevelSublevelsNumber of OrbitalsTotal Number of Electrons1234s12s p1 + 3 = 42 + 6 = 8s p d= 9= 18s p d f= 16= 32
11The First Energy LevelThe first energy level is the lowest energy level in all atomsThis level only has an s sublevel and can only hold two electrons because it has only 1 orbital
12The Second Energy Level Second lowest energy levelHas as s sublevel and a p sublevelThe 2s sublevel has one orbital and can therefore hold 2 electronsThe 2p sublevel has 3 orbitals and can therefore hold up to 6 electrons
13The Third Energy LevelThe third energy level has three sublevels s, p, and dThe 3s and 3p sublevels have the same number of orbitals as 2s and 2pThe 3d orbital has 5 orbitals andCan therefore hold up to 10 electrons
14The Fourth & Higher Energy Levels The 4th energy level has 4 sublevels: s, p, d, and fThe 4s, 4p, and 4d are all the same shape, except bigger than lower energy levelsThe 4f sublevel has 5 orbitals
15Electron Arrangement in Atoms There are three rules to help us understand where electrons are in the electron cloudAufbau principle – electrons will occupy the lowest energy level possiblePauli Exclusion Principle – only two electrons may occupy an orbital and they must have opposite spin (clockwise and counterclockwise)Hund’s Rule – when filling a sublevel such as 3p, e- will go to an empty orbital prior to pairing up (spread out before pairing up)
16Writing Electron Configurations Electron Configurations tell you the ground state location of each electron in an atomExample 1: What is the Electron Configuration of nitrogenFirst of all, how many electron does a nitrogen atom have?7Example 2: What is the Electron Configuration of siliconFirst of all, how many electron does a silicon atom have?14# of e-Energy Level1s22s22p3Sublevel1s22s22p63s23p2
17The Energy of OrbitalsHigher sublevels do not necessarily have a higher energyThe order from lowest to highest energy is as followsLowest EnergyHighest Energy1s2s2p3s3p4s3d4p5s4d5p6s4f5d6p7s
18A Trick 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d 6f 7s 7p 7d Fill the sublevels in the order that the arrows pass through, beginning with the top arrow.2s2p3s3p3d4s4p4d4f5s5p5d5f6s6p6d6f7s7p7d7f
19Comprehension CheckWrite the electron configurations for the following elementsBe, Mg, S, Ar, Sc, Fe, Ge, Kr, Tc
20Comprehension CheckWrite the electron configurations for the following elementsBe1s2 2s2Mg1s2 2s2 2p6 3s2S1s2 2s2 2p6 3s2 3p4Ar1s2 2s2 2p6 3s2 3p6
21Comprehension CheckWrite the electron configuration for the following elements.Sc1s2 2s2 2p6 3s2 3p6 4s2 3d1Fe1s2 2s2 2p6 3s2 3p6 4s2 3d6Ge1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p2Kr1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6Tc1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 5d10
22Congratulations, you can now write long electron configurations!