CHM 2200 Exam 1 Study Guide CH 1 13 I Review of Gen Chem A Covalent Bonds 1 Covalent Bond formed by the sharing usually involved when singly occu pied valence orbital overlaps another of electrons between atoms instead of complete transfer of electrons from one atom to the other 2 General Rule a atom shares enough electrons to reach a noble gas configura 1 Share 2 electrons single bond 2 Share 4 double 3 Share 6 triple 4 If unequal sharing polar covalent tion a For example Hydrogen has 1 covalent to fill 1s 2 b Carbon in 4A needs four covalent bond c See picture below Image 1A 3 4 5 If an atom loses one or more electrons becomes charged called cation If atom gains 1 or more electrons it comes anion B Covalent vs Coordinate Covalent Bond 1 Covalent shared electrons from different atoms bond is result of the overlap of 2 slightly filled orbitals think half and half so electrons come from both atoms 2 Coordinate Covalent bond that is formed by the overlap of a filled or bital with a vacant orbital on other atom So both electrons come from the same atom 3 See picture below Image 2A 4 C Drawing Lewis Structures simple steps 1 Step 1 Find Total Valence Electrons 1 Depending on which group see image 1A 2 Ex 3 5 3x7 total 26 electrons PCl3 Phosphorus Group 5A 5 valence and Cl 7A 7 valence 2 Step 2 Find to make happy aka fill outer electron shell 1 Elements up to period 4 on the periodic table need 8 electrons called octet rule 3 Step 3 Determine of Bonds 1 Step 2 tells how many electrons needed and step 1 how many have Subtract step 1 from the number in step 2 gives of electrons needed to complete octet remember each bond needs 2 electrons 2 Step2 Step1 2 4 Step 4 Choose Central Atom that is the least electronegative one or with highest valence 1 Recall central atom up to 4 other atoms connected 5 Step 5 Draw Skeletal Structure 1 Use straight line to represent bond 6 Step 6 Place Electrons around outside atoms 1 Complete octets around outside atoms if not enough electrons than structure from Step 5 if not enough step 5 wrong 7 Step 7 Place remaining electrons around central atom 1 Complete octet for central atom with remaining electrons any bonds left from step 3 make double bonds 2 SEE THIS VIDEO FOR HELP 3 http www youtube com watch v 8JsK6rPpi70 D VSEPR Valence Shell Electron Pair Repulsion 1 molecules have specific shape that depend on number of electron bonds and lone pairs 2 Atoms with 2 electron charge clouds linear geometry 3 Atom with 3 charge clouds planar triangular geometry 4 Atom with 4 charge tetrahedral geometry 109 5 de 180 degrees 120 degrees grees 5 Image 3A 6 E Polar Covalent Bonds Review 1 Bonds are polar covalent if the bonding electrons are not shared equally between the atoms 2 The ability to attract electrons in covalent bonds is elec tronegativity highest upper right of periodic table and lowest lower left 3 word of caution be aware of just because molecule has polar covalent does not make it polar see differ ences in picture below Water is polar versus CO2 not 4 Image 4A 5 6 Image 7 A II Chapter 12 Alkanes A Why is Carbon so Special 1 Carbon is Tetravalent it always forms 4 bonds 2 Abundant rich chemistry lots of different compound combinations etc 3 Can make single double or triple bonds can form strong Pi Bonds 4 Create stable diverse structures instead of inorganic compounds such as NaCl which has a high melting and boiling points because high number of oppositely charged molecules create very strong attraction Or ganic molecules are joined by covalent bonds which are weak non ioinic bonds they have a relatively low melt ing and boiling point leads to them being liquid at room temp 5 Also organic compounds are usually insoluble in water and can have important consequences such as oil spills etc 1 18 million organic molecules been described with unique properties etc We can understand them according to their structural fea tures that the chemical behavior is often predictable based on specific grouping These specific groups are called functional groups characteristic physical and chemical properties And are a part of a larger molecule an atom or group of atoms that has a 2 Functional group B Functional Groups 3 THE CHEMISTRY OF ORGANIC MOLECULES MOSTLY DE TERMINED BY ITS FUNCTIONAL GROUPS NOT ITS SIZE OR COMPLEXITY 4 First 4 are Hydrocarbons consist only of carbon and hydrogen bonds alkane alkene alkyne aromatic 5 Next 4 contain only SINGLE bonds and have carbon bonded to an electronegative atom ex Cl F Br I O or N a C halogen Alkyl Halide b C Oxygen alcohol c Two C Oxygen single bonds to each Ether d C Nitrogen Amine 6 The last remaining functional groups contain carbon oxygen DOUBLE BONDS a ALDYHYDE b c KETONE CARBOXYLIC ACID d e f ESTER ANHYDRIDE AMIDE basically only C O with a N on molecule C General Formula Cn H2n 2 1 N of carbons 2 Ex n 3 3 C3H 2x3 2 C3H8 D Classifying Carbons as Primary 1 Secondary 2 Teteriary attached to 4 Quaternary 5 is based on how many other carbons the carbon in question is con nected to See Image 1B BELOW E F Compounds with the same molecular formula but different structural formulas are called ISOMERS 1 Example see picture below different ISOMERS of C5H12 2 Image 8A 3 G Image above has 3 constitutional isomers are com pounds with the same molecular formula but with differ ent connections among their atoms a Also notice the branched and unbranched b Constitutional isomers have DIFFERENT alkanes above STRUCTURES PHYSICAL PROPERTIES melt ing and boiling points H EASY SUMMARY OF LEWIS STRUCTURAL LINE AND CONDENSED WAY OF DRAWING COMPOUNDS See formal charge explanation end of guide I Conformation the specific 3 dimensional arrangement of atoms in a molecule J Here we see CONFORMERS which are molecular struc tures having idenical connections between atoms K How to tell between Conformers and Isomers 1 Simply name the 2 compounds using IUPAC which will be explained next 2 IF THEY HAVE THE SAME NAME THEY ARE CONFORM ERS IF THEY HAVE DIFFERENT NAMES BUT THE SAME FORMULA THEY ARE ISOMERS L How to Name Nomenclature Compounds Image 9A 1 Step 1 Name the Longest Chain see image 8A above 2 Step 2 Number the Chain of Carbons so that the lowest number near branched point or first substituent 3 Step 3 Identify Substituents See Image 10A below Image 10A 4 Step 4 Write Name as single Word 5 Write name so that substituents are in ALPHABETICAL 6 if more than 1 of same substituent use pre fix di order tri tetra 7 Ignore Prefix di tri tetra for