Organic Chemistry CHEM 233
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This 2 page Class Notes was uploaded by Rosendo Conn on Saturday September 12, 2015. The Class Notes belongs to CHEM 233 at West Virginia University taught by Staff in Fall. Since its upload, it has received 20 views. For similar materials see /class/202845/chem-233-west-virginia-university in Chemistry at West Virginia University.
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Date Created: 09/12/15
Chem 233 Review Sheet for Chapters 1 amp 2 LEWIS STRUCTURES Ste s or Drawin Count up the total number of valence electrons in the structure NOTE ForA Group elements the number of valence electrons is equal to the Group number Decide on a skeletal structure what s bonded to what a The central atom is generally written rst in the chemical formula b Hydro gen is never the central atom but is usually written rst in acids Place two electrons in each bond Surround each of the noncentral atoms with an octet of electrons NOTE Hydrogen is an exception and is only surrounded by two electrons Determine how many electrons are le Place any remaining electrons on the central atom in pairs If the central atom does not have an octet of electrons form double or triple bonds to give it an octet of electrons NOTE H B Be F and metals do not generally form multiple bonds If the central atom in Step 6 does not form multiple bonds leave it short of electrons NOTE H is generally surrounded by 2 electrons Be by 4 electrons and B by 6 electrons Valence Number of bonds that an atom of an element likes to form in covalent compounds This is also equal to the number of e needed to complete the octet Use valences to easily and quickly draw Lewis structures for organic substances Common Valences Non metals in Groups 3 M E m M 1 4 3 2 1 Example Carbon in Group IVA has a valence of 4 and consequently likes to form 4 bonds These four bonds can consist of four single bonds one double and two single bonds one triple and one single bond two double bonds COPS Electronegativity Q Difference in electronegativity 39 ED Polar covalent bonds 1 Ability of bonded atom to attract ie inductively pull electrons in bond toward itself 1 Increases in value as proceed across the periodic table within a row from Group IA to Group VIIA Note Electronegativity of Group VIIIA elements is zero 2 Decreases in value as proceed down the periodic table within a column 3 In general nonmetals igthigh migtelectronegative metalsigtlow m igtelectropositive Value of 39 m gives information on type of bond and compound present If39 m 39 20 Ionic bonds are present between ions EX NaF en F40 Na09 If 39 m 0 Covalent bonds are present between atoms EX F2 en F40 Polar covalent bonds are present between atoms EX HCl en Cl32 H22 IfO lt r m lt 20 Have a character intermediate between covalent and ionic bonds 2 In a polar covalent bond electron pairs are shared but not equally The electron pair spends more time near the more electronegative atom giving this atom a partial negative charge Formal Charge Charge on atom in given Lewis structure A formal charge of 1 means that the atom has one less valence e surrounding it than the neutral atom A formal charge of 2 means that the atom has two more valence e surrounding it than the neutral atom T 0 calculate Formal Charge Valence e 12X bonding e nonbonding e 0R Formal Charge Valence e bonds nonbonding e
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