Intro to Organic Chemistry
Intro to Organic Chemistry CHEM 2300
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Reviews for Intro to Organic Chemistry
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Date Created: 10/28/15
Take Home Review Concepts for Chapter 1 CHEM 2300 Spring 2003 Ionic and Covalent Bonding Lewis Structures Electronegativity and Polarity Orbitals and Electronic Structure Amwe Answers to problems can be found on the course web site wwwuwyoeduchem2300 Review Concepts for Chapter 1 CHEM 2300 Spring 2002 Chemical Bonding Valence electrons are the e39 in the highest energy level of an atom Being further from the nucleus they are more accessible and less tightly held These are the e39 that are used in chemical bonding valence e39 for a main group element its main group column 18 1 Label the main group element sections on the periodic table at the right 2 How many valence electrons do each of the following possess a C b Cl c H d Na A useful rule of thumb about bonding is the octet rule When forming compounds atoms gain lose or share electrons such that they achieve a stable noble gas electronic con guration of eight valence electrons except H which gets 2 Ionic compounds are formed between metals and nonmetals Metal loses e39 forms a positively charged cation Nonmetal gains e39 forms a negatively charged anion Q 9 K Br gt K Br Example KBr quot I valence e39 7 valence equot 8 valence e39 8 valence e39 like Ar Molecules or covalent compounds are formed between atoms of nonmetals by sharing pairs of electrons covalent bonds gt E 5 Example F2 quot quot 7 valence equot 7 valence e39 By sharing 2 electrons one from each F each F has 8 electrons around itself 3 Label the metal and nonmetal sections on the periodic table at the right 4 Is H considered a metal or nonmetal 5 What type of bonding will you nd in each of the compounds below If ionic which element will be the cation and which will be the anion a CS2 b MgBr2 c NaH d CH3ONa Bonding in Organic Compounds For the most part organic compounds are composed of carbon and a few other elements H O N P S and the halogens X 6 Given the above statement organic compounds will be composed of what type of bonds Lewis Structures We show how atoms are connected and how the valence electrons are distributed in a compound by drawing Lewis dot structures quot 3 H gt H N H Example NH3 quot 5 valence e39 I valence e39 H 1011 By sharing electrons N has 8 electrons around itself and each H has 2 Terms Valence electrons not involved in bonding are called lone pair or nonbonding electrons A pair of shared electrons is called a single bond and is represented in electron dot structures by a pair of dots or a line p lone pair H N H or H H H single bond Multiple Bonding Sometimes bonding atoms must share more than 2 electrons to achieve octets A double bond is composed of 4 electrons and is represented by 2 lines A triple bond is composed of 6 electrons and is represented by 3 lines 20 C or IZOCO39 H C C H or H CEC H Electronegativity and Polarity Atoms in molecules share electrons but these electrons are not necessarily shared equally Electronegativity X is a measure of the ability of an atom in a molecule to attract shareal electrons to itself increases Some electronegativity values Trends a Electronegativity increases from bottom to top and from left to right in the periodic table b C and H are less electronegative than the halogens and other nonmetals in the second period except B The more electronegative atom in a bond will pull more electron density from the bond toward itself As a result partial positive and partial negative charges develop For example 8 8 l gt C O or 0 0 quotdelta quotdelta The arrow points toward plus quot minus quot the more electronegative atom Notice the tail Polar anal Nongolar Covalent Bonds If the electronegativities of the two atoms are similar there will be little polarization of electron density little charge buildup and the bond is said to be nonpolar If the electronegativities are significantly different significant polarization and charges will build up and the bond is said to be polar and has a dipole In particular remember the polarity of these important bonds involving H 8 8 H O polar bonds but H C is nonpolar 8 8 H N 7 Without consulting the electronegatiVity table using only the periodic table and the trends noted use the 6 5 convention to show the polarization of each of the following bonds a S 0 0 C 0 e C Br g N H b S P d P O f C H 8 Using the dipole arrow convention show the polarization of each of the following from problem 8 a 3 0 c C O e C Br g N H b 3 13 d P O f C H Orbitals and Electronic Confi urations Orbitals are areas in space around the nucleus of an atom where there is a high probability of nding electrons Orbitals are given letter symbols s p d f and have the following shapes SQ p8 c188 You only get one s orbital at a time but p orbitals come 3 to a set d 5 to a set f 7 to a set The orbitals within a set differ with respect to their orientation along the x y z axes z Z Z y y y x X X px Py pz Each individual orbital holds 2 electrons maximum An s orbital can hold 2 e39 a set ofp orbitals 7 6 e39 a set ofd 7 10 e39 and a set off7 14 e39 The electronic con guration of an atom lists the orbitals which have electrons in them in order of increasing energy using superscripts to indicate the number of electrons in each orbital The energy lling ordering can easily be read off the periodic table knowing where the s p d and fblocks are For example Ge Z 32 ls22s22p63s23p64s23d104p2 A x 2915 S P 18 3d 315 d Ac zlsA39p 4d 4f I39Ss 5p 5d 5f Hund s Rule states that when lling a set of orbitals of equal energy electrons are added singly with parallel spins before pairing them up For example E E m Now REES 252 213 ls2 2s2 2p3 ls2 The valence shell of an atom is the set of orbitals with the highest numerical label principal quantum number 9 What is the electronic con guration of C Cl 10 What is the valence electronic con guration of C Cl 11 Using Hund s rule show the arrangement of e39 in C among its orbitals CHEM 2300 Spring 2003 Chapter 1 Review Answers 1 Main group Transition elements 2 a4 b7 cl d1 3 Nonmetals Metals H 4 Nonmetal 5 a covalent b ionic Mgzl cation Br39 anions c ionic Na cation H39 anion d both covalent bonding between C H amp O atoms and ionic bonding between Na and 39OCH3 6 Covalent 8 8 8 5 8 8 5 8 7 a 30 c CO e CBr g NH 8 8 8 8 b SP d PO f CH nonpolar gt gt 4 I 8 a 80 c CO e CBr g NH gt b SP d PO f CH nonpolar 9 ls22s22p2 ls22s22p63s23p5 10 2s22p2 3s23p5 11 C is E E EH 2 2 2 ls 25 2p