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Chapter 8

CHEM UA 125- Chapter 8 Notes

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John Halpin

original periodic table Mendeleev periodic law when arranged by atomic mass the elements exhibit a periodic recurrence of similar propertiesmodern periodic table Moseley arranges the elements by atomic number not by massHow does the electron configuration of an element relate to its chemical and physical propertiesthe distribution of electrons within the levels and sub levels of its atoms81in many electron atoms these features become importanta fourth quantum numbera limit on the number of electrons in an orbitala splitting of energy levels into sub levelsn l and ml describe the sizeenergy shape and orientation of an atomic orbitaladditional quantum number describes the spinspin is a property of the electron not the orbitalspin quantum number 12 or 12each electron in an atom is described completely by a set of 4 quantum numbersthe first 3 describe its orbital and the fourth describes its spinHydrogen n1 l0 ml0 ms 12exclusion principle no two electrons in the same atom can have the same 4 quantum numbersan atomic orbital can hold a max of two electrons and they must have opposing spinselectrons have paired spinsthe energy states of many electron atoms are also affected by electronelectron repulsionsresult in the splitting of energy levels into sub levels of differing energiesenergy of a many electron atom depends mostly on n and to a lesser extent on lenergy difference arises from nuclear attraction electron repulsion and orbital shape which leads to shielding and penetrationa higher cycler charge increase nucleuselectron attractions and thus lowers sub level energy stabilizes atomshielding reduces the full nuclear charge to an effective nuclear charge zeff the nuclear charge an electron actually experiences makes electron easier to removeelectrons in the same energy level shield each other somewhatinner electrons cause a much lower zeff than electrons on the same levelinner electrons shield very effectivelypenetration increases the nuclear attraction for a 2s electron vs a 2p electron decreases the shielding of a 2s electron by the 1s electronspenetration and the resulting effects on shielding cause an energy level to split into sub levels of differing energythe lower the l value the more its electrons penetrate the more the attraction to the nucleusa lower l value indicates a more stable lower energy sub levelspdf82ground state electron configuration the lowest energy distribution of electrons in the sub levels of its atomsthe recurring pattern in electron configurations is the basis for recurring patterns in chemical behavrioaufbau principle start at the beginning of the periodic table and add one proton to the
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