Atomic and Molecular Polarity

Atomic and Molecular Polarity

Atomic and Molecular PolarityA matter of shape andelectronegativity

Recall that not all atoms arecreated equalDecreasing ElectronegativityIncreasing shieldingIncreasing ElectronegativityIncreasing nuclear chargeHalogens: VeryelectronegativeAlkali Metals:Not veryelectronegative

Bond character results fromunequal sharingLi + F - H OVERY unequal sharingIONIC BONDCCMore equal sharingPOLAR COVALENT BONDDecreasing EN differencesEqual sharingCOVALENT BOND

Molecular polarity comes partlyfrom molecular shapealencelectronhellThe short form:Electrons are like supermodels, they HATEeach other. They will arrange themselvesto maximize the distance between them.airepulsion

Steps to predict shapealencelectronhellairepulsion1. Draw Lewis Structure for themolecule in question2. Count the number of “electrondomains”. Multiple bonds count asone “domain”3. Predict appropriate shape for thenumber of domains

Shapes and number of domains# ofdomains23MolecularshapeLinearTrigonal4Tetrahedral

Polarity from molecular shapeUnshared pairs create negative polesExampleCH 4NH 3H 2 OPolarityNoYesYes

Polarity from bond polarityCOMolecular geometry predicts that this is a non-polar moleculreOxygen is slightly more electronegative than carbon, so thismolecule is slightly polar

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