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Chapter 1

CH 320M Chapter 1 Textbook Notes

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CH 320M
John A.Colapret

1.1 ElectronicStructure of Atoms Tuesday, May 14,2013 4:22 PM Organic chemistry - study of carbon compounds Atom - small, dense nucleus made of neutrons and protons • Most of the mass is in its nucleus ○ Nucleus surrounding by electrons • Identified by principle quantum numbers (1, 2, 3, etc.) ○ Diameter of 10-14to 10-1meters ○ Each shell can have up 2n electrons Shells - regions of space where you can find an electron  N = number of the shell • Energy of electrons in shells are quantized [only specificvalues of energy are possible] • Divided into subshells(letters s, p, d and f) ○ Orbital - region of space that can hold 2 electrons and has a specificquantized energy  Orthogonal - having no net overlap  • 3 important effects: ○ Electrostatic attraction to the nucleus ○ Electrostatic repulsion between the electrons ○ Wavelike nature of an electron that prefers to be delocalized  Delocalization - spreading of electron density over a larger volume space Chapter 1 Page 1 Example Tuesday,May14, 2013 5:03 PM PERIODIC TABLE REPRESENTING S, P, D, AND F BLOCKS: Chapter 1 Page 2 Electron Configurations of Atoms Tuesday, May 14, 2013 5:08 PM Ground-stateelectron configuration-the LOWEST energyelectron configuration for an atom or molecule 3 RULES TO FIGURE OUT THE CONFIGURATIONOF AN ATOM/MOLECULE: 1. Rule 1: the AUFBAU ("Build-Up") Principle a. Orbitals fill in order of increasing energy i. From lowest to highest ii. Concerned with first, second, and third periods of the table 2. Rule 2: the PAULI EXCLUSION Principle a. Only TWO electrons can occupy an orbital b. Their spins must be paired i. 3. Rule 3: HUND'S Rule a. When orbitals of equal energy (called degenerate)are availablebut there aren't enough electrons to fill all of them completely, one electron is put in each before a second electron is added to any b. The spinsof the singleelectrons in the degenerate orbitals should be aligned EXAMPLE: Energy-level diagrams - pictoriallydesignate whereelectrons are placed in an electron configuration (as above^) Concept of Energy Tuesday, May 14, 2013 5:10 PM Energy - abilityto do work Potential energy - the energythat can be released ifgivenan opportunity Ground state - the lowest energy state of a system Excited state - a state of a system at higherenergythan the ground state All of natureseeksits LOWEST energy state…! Ionization potential - the energy needed to removethe most looselyheld electron from an atom or a molecule • The moreeasy to remove the energy, the lowerthe ionization potential Lewis Dot Structures Tuesday, May 14, 2013 5:18 PM Valence electrons - electrons in the outermost shell of an atom Valence shell - outermost occupied electron shell of an atom Lewis dotstructure - symbol of elementsurrounded by a number of dots (namedafter GilbertN. Lewis) 1.2 Lewis Model of Bonding Tuesday, May 14, 2013 5:28 PM OCTET RULE: group 1A-7A elementsreact to achieve an outer shell of 8 valence electrons Formation of Chemical Bonds Tuesday, May 14, 2013 5:31 PM Ionic atom - lose or gainelectrons to acquire a completelyfilledvalence shell Anion - negativelycharged ion (gainselectrons) Cation - positivelycharged ion (loseelectrons) OPPOSITES ATTRACT! - EX: NaCl [ionic interaction --- ionic bond] Covalentbond - an atom may share electrons with one or more other atoms to complete its valence shell Polar covalentbonds - bonds that are partiallyionic and partiallycovalent Electronegativity andChemicalBonds Tuesday, May 14,2013 5:42 PM Electronegativity - measure of an atom's attraction for electrons that it shares in a chemical bond with another atom Electronegativity increase from left to right Atom gets smaller from left to right Electron affinity - energy added or released when an electron is added to an atom or molecule • Becomes more favorable as you move from left to right Chapter 1 Page 9 Formation of Ions Tuesday, May 14, 2013 5:52 PM Ions - formed by the transfer of electrons from valenceshell of an atom of lower electronegativityto higher Ions form when the difference in electronegativitybetween interacting atoms is 1.9< Covalent Bonds Tuesday, May 14, 2013 5:56 PM Covalentbond - atoms sharing of one or more pairs of electrons to givea noble gas configuration at each atom • Ex: hydrogen molecule ○  Bond dissociation enthalpy - sameamount of energythat would have to be absorbed to break the bond Bond length - distance between nuclei in a covalent bond Lone pair - unshared pair of electrons on an atom FILLED VALENCE SHELLS = STABLE Polar Covalent Bonds Tuesday, May 14, 2013 6:06 PM Homonuclear diatomics: H2, N2, O2, and F2 [nonpolar covalent bonds] Partial negative charge Partial positive charge Example: Bond dipole moment - measure of the polarity of a covalent bond; product of the charge on either atom of a polar covalent bond times distance between the nuclei • SI unit: coulomb*meter • Symbol: µ Nonpolar covalent bond - covalent bond between atoms whose difference in electronegativity is <0.5 Polar covalent bond - covalent bond between atoms whose difference in electronegativity is between 0.5 and 1.9 Chapter 1 Page 12 Example Tuesday, May 14, 2013 6:14 PM Chapter 1 Page 13 Lewis Structures for Molecules and Polyatomic Ions Tuesday, May 14, 2013 6:19 PM 1. Determine the number of valance electrons in the molecule or ion a. Add the # of valence electrons contributed by each atom b. For ions i. Add one e- for each negative charge on the ion ii. Subtract one e- for each positive charge on the ion 2. Determine the arrangement of atoms in the molecule or ion a. Isomers - different compounds with the same molecular formula i. 3. Connect the atoms with single bonds --> arrange the remaining electrons in pairs so that each atom in the molecule has a complete outer shell a. Each hydrogen = surrounded by 2 electrons b. Each C, O, N, and halogen = surrounded by 8 electrons [octet rule] 4. Electron pairs shared (single line is shown) [bonding electrons] Unpaired electrons (pair of dots) [nonbonding electrons] 5. Single pair of e- shared = single bond Two pairs shared = double bond Three pairs shared = triple bond Chapter 1 Page 14 Example Tuesday, May 14, 2013 6:33 PM Formal Change Tuesday, May 14, 2013 6:34 PM Formal charge - charge on an atom in a moleculeor polyatomic ion 1. Write a correct Lewis structure for the moleculeor ion 2. Assignto each atom all its unshared (nonbonding) and half its shared (bonding electrons) 3. Comparethis # with number of valence electrons in neutral, unbonded atom a. 4. Sum of all the formal charges is = to the total charge on the molecule Example Tuesday, May 14, 2013 6:42 PM Exceptionsto the Octet Rule Tuesday, May 14, 2013 6:44PM One group ofexceptions:Group 3A Example: BF3 Becausetheir valence shells are only partially filled -->trivalent compounds ofboronand aluminumexhibit a high reactivity with compoundsthat have extra electrons-->octet filled! Chapter 1 Page 18 1.3 Functional Groups Tuesday, May 14, 2013 6:46 PM Functionalgroups - an atom or group of atoms within a molecule that shows a characteristic set of physical and chemical properties Alcohols Tuesday,May 14, 2013 6:49 PM Alcohol - compound containing an -OH (hydroxyl) groupbonded toa tetrahedralcarbon atom Condensedstructuralformula -more abbreviated form Different ways to show a formula: Alcohols are classified as: ----depending on the number of carbon atoms bonded to the carbon bearing • 1 degree = primary • 2 degree = secondary • 3 degree = tertiary Example Tuesday,May 14, 2013 6:52 PM Chapter 1 Page 21 Amines Tuesday, May 14,2013 6:55 PM Aminogroup- nitrogenatom bonded to 1, 2 or 3 carbonatom(s)by singlebonds • Primary(1 degree)amine • Secondary(2 degree)amine • Tertiary(3 degree)amine Chapter 1 Page 22 Aldehydes and Ketones Tuesday, May 14, 2013 6:58PM Carbonyl - C=O functional group of both aldehydes and ketones Aldehyde- a compound containing ---CHO group • Simplest aldehyde = formaldehyde (CH2O) • Can be written as ---CH=O or ---CHO Ketone - a compound containing a carbonyl group bonded to two carbons Chapter 1 Page 23 Carboxylic Acids Tuesday, May 14,2013 7:02PM Carboxylic acid - compound containing a carboxyl ---COOH group • Carbonyl + hydroxyl group Example: Chapter 1 Page 24 Carboxylic Esters Tuesday, May14, 2013 7:03PM Carboxylic esters- derivative of a carboxylic acid in which the H of the carboxyl group is replaced by a carbon-containing group Example:
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