Review: Atoms and Orbitals. Electrons = and charged; held

Transcription

1 hapter 1 Review: Atoms and Orbitals 1.1 Molecules are composed of Atoms be broken into smaller, stable units (except by physicists Elements are : Pb Au Atom = Nucleus + Electrons: Nucleus =,, charged core Electrons = and charged; held Example: protons neutrons electrons atomic wt. N Rutherford: electrons Bohr: electrons Schrödinger: electrons d orbital 4-lobed - highest electron density at p orbital bilobed - highest electron density at s orbital spherical - highest electron density at s orbitals lowest in energy because p orbitals higher in energy because d orbitals even higher in energy because Because s orbitals are they have only orientation Because p orbitals are they have orientations:,,

2 ybrid Orbitals 1.2 ybrid orbitals = combination of orbitals + = s p sp electron density on one than other 3 Types of hybrid orbitals # hybrid orbitals: Total # orbitals: "sp 3 " = "sp 2 " = "sp" = Shape: Interorbital angle: To determine the hybridization count the # of attached. Examples: What are the bond angles in the following molecules? N l O S l N O O

3 Nature of the hemical Bond 1.3 Ions and Ionic Bonds Li Li F F 1s 2s 1s 2s 1s 2s 2p x 2p y 2p z 1s 2s 2p x 2p y 2p z with with Both ions are stable because Li + F Li F a. of electron gives b. Li F held together by,, forces c. LiF forms vast _ of atoms ovalent Bonds Some atoms do not readily ; they For example: + where the line represents = bond carbon has valence e hydrogen has valence e

4 ovalent Bonds (cont'd) 1.4 Octet Rule (of Thumb): Second row atom will form bonds until they have captured electrons N Violation of the Octet Rule Elements in the routinely transgress the octet rule PO 4 3 P SF 6 S Even 2nd row elements can violate octet rule: they can have 8 e, but more B BF 3 3 (Both of these are ) "Lewis" structures Lewis electron dot structures show when are found in molecule Bonds are both the location of chemical and _ Rules for drawing Lewis structures: a. ount total # of O b. Draw skeleton connecting c. Add (remember octet rule!) O d. Add _ e. Add F.. = (# valence e ) (# L.P. e ) (# bonds) O 3 N 3 N 2 3 NO 2 N 4 3 Br

5 ovalent Bonds (cont'd) 1.5 There are two types of covalent bonds: sigma (σ) pi (π) P _ overlap _ overlap overlap = bond overlap = bond electron density is electron density is ovalent Bond: Bonds formed by of 2 _ Sometime the 2 e are shared F F covalent Sometime the eletron sharing is F 3 O covalent Why are the electrons distributed unevenly? Electronegativity is the of an atom to _ electrons The electronegativity scale goes from to The ordering of common elements by increasing electronegativity is: Electronegativity across a row of the periodic table because Electronegativity down a period (column) of the periodic table Polar covalent bonds form when electronegativity differences between atoms are. Non-polar covalent bonds form when electronegativity differences between atoms are. Which is more polar: 3 or 3 F 3 O or 3 Br

6 Drawing Organic ompounds Molecular formula gives the and of atoms, but not pentane Lewis structures show additional information: pentane 3. Lewis structures are tedious to draw. _ notation faster pentane concise but contains "hidden" information: a) & are s b) not shown; add until is onvert the following Lewis structures to skeletal notation

7 Alkane Nomenclature 1.7 Alkanes are containing only bonds Nomenclature of simple alkanes point and point increase with the number of Nomenclature of complex alkanes 1. Find longest chain. This give root name. Prefixes 2. Number carbons from end nearest branch point Identify # s in substituent. This give you prefix Locate position of substituent. 5. Name = location - prefix - root

8 Structural Isomers 1.8 Structural isomers have the same and of atoms, but different Example These however are all the same: Draw all the isomers of 6 14 ycloalkanes Prefixes

9 Structural Isomers (a.k.a. onstitutional Isomers) 1.9 Are propane and cyclopropane structural isomers? b/c they have _ (Draw structures. ount s and s. Write M.F.) Saturated vs Unsaturated For s, the maximum # of s is. It is fully, no more s can be yclopropane M.F. is. Is it fully saturated?. Where would you add s? All ring compounds contain Geometric Isomers Geometric isomers have same, but different 3D arrangement could be or Draw skeletal structures for: cis-1-methyl-2-ethyl-cyclobutane trans-1,4-dimethyl-cyclohexane

10 Alkane Stability 1.1 ydrocarbons are generally and. They are used as oil and lubricants. ydrocarbons have one very useful property. They are combustible: + O O + O + ow much heat? Depends on the chemical structure. eats of combustion (kcal/mol) Δ c Δ c Δ c /carbon eats of combustion are an indirect measure of 1. Are these reaction exothermic or endothermic? Why? 2. igher Δ c represents stable compound. Why? 3. Why is the heat of combustion greater for ethane than methane? 4. What is the trend in heats of combustion from pentane to 2-methyl-butane to 2,2-dimethyl-propane? 5. What is the trend in heats of combustion from small-ring cycloalkanes to large-ring cycloalkanes? Explain. 6. Why does the heat of combustion per carbon decrease from cyclopropane to cyclohexane?

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