Chemistry Bonding Notes and Lewis Dot Structures

CChemistry Exam #2 Study Guide (10/07/12) I. Bonding a. Ionic Bonding i. Electrons are transferred ii. Ions are held together by electrostatic force b. Covalent Bonding iii. Electrons are somehow shared iv. Electrons are attracted to nuclei (shared) II. Electronegativity c. The ability of an atom in a molecule to attract shared electrons to itself d. Measured on Pauling Scale e. Most electronegative: Fluorine. Then Oxygen. f. Depending on electronegativity of X and Y, there are 3 possibilities: v. X and Y have identical electronegativities (Non Polar) vi.X and Y have dissimilar electronegativities (Polar)- Y is slightly negative; has greater control than slightly positive X vii. X and Y have very different electronegativities (Ionic)- Y is negative; has full control g. Polar Covalent viii. Size depends on electronegative difference ix. Arrow points to where electrons are dragged to x. Dipole Moment measured in Debyes (D) 1. [Dipole Momenti = Q*r] xi. Possesses some ionic character 2. The bigger the difference†¦ a. The more polar the bond b. The bigger the dipole c. The more ionic in character III.Electron Configuration for Ions h. Atom forms an ion with electron configuration of the closest noble gas xii. True for representative S and P block xiii. Atom will lose up to three or gain up to three electrons 3. For D-block elements d. Outer S electrons lost before outer D electrons 4. For P-block elements e. Outer P lost before the outer S electrons, which are lost before outer D IV. Ionic Radii i. Size descriptions based on charge xiv. Positive ions are always smaller than the parent atom xv. Negative ions are always larger than the parent atom j.Periodic trend xvi. Ionic radii increase within a column going from top to bottom xvii. Ionic radii decrease within a row going from left to right V. Isoelectronic Ions k. Have the same number of electrons l. Radius decreases as atomic number increases VI. Compounds m. Ionic xviii. High Melting Point and Boiling Poin t (brittle solids) xix. Soluble in polar solvents like water xx. Insoluble in nonpolar solvents like Hexane xxi. Metal and Nonmetal xxii. Any compound that conducts electric current when melted n. Covalent xiii. Low Melting Point and Boiling Point (solid/liquid/gas) xxiv. Insoluble in polar solvents (exception: Sugar! ) xxv. Soluble in nonpolar solvents xxvi. Nonmetal and Nonmetal o. Crystals xxvii. All group 1 Alkali metals and Group 7 Halogens make crystals xxviii. Sublimation: solid to a gas! VII. Lattice Energy p. Measure of how strongly ions interact together (compares sizes of ions) xxix. enthalpy of formation of the ionic compound from gaseous ions and as such is invariably exothermic xxx. he energy required to completely separate one mole of a solid ionic compound into gaseous ionic constituents q. Goes to closer energy (emits energy as heat)- always more negative number r. (+) = endothermic (absorbing energy) s. (-) = exothermic (releasing energy) t. Energy is released! xxx i. =K[(Q1Q2)/(r)] xxxii. Large for small â€Å"r† (average distance between ions)- higher boiling point, more stable, difficult to separate, but still fragile xxxiii. Large â€Å"Q†- highly charged xxxiv. Lattice energy goes down in same group VIII.Bond Order u. Triple Bond (as bond energy increases, bond length decreases! ) xxxv. Highest Bond Order xxxvi. Strongest xxxvii. Shortest v. Double Bond w. Single Bond xxxviii. Weakest xxxix. Longest xl. Lowest Bond Order IX. Resonance x. More than one Lewis Dot Structure can be drawn for the same arrangement (skeleton) of atoms. Only the bonds differ! y. True structure is a ‘hybrid’ or ‘blend’ of possible resonance structures z. Not double or single bonds, but all bonds with order 1. 3333 {. Shuffling of electrons |. Formal Charge li. Look at one atom at a time (sum of Formal Charge must add up to over all charge of structure) xlii. (# of valance e- on free atom) – [(# of lone pair e-) + (# o f bonds)] X. Octet Rule Violators }. Always OBEY the octet rule: B, C, O, N, and F. ~. 5 EXCEPTIONS we should know: xliii. ________________________ . Radical- odd number of electrons . Biradical- EVEN number of electrons – has TWO UNPAIRED electrons (O2) . Groups 5-8 (3rd row and lower can have more than 8 valance) XI. VSEPR Theory . â€Å"Valance Shell Electron Pair Repulsion† Bonds and lone pairs repel (more lone pairs= squeezed) . Determines the likely shape of a molecule . Does not describe how the bonding occurs . Steps: xliv. Draw Lewis Dot Structure xlv. Count RHED (Region of High Electron Density) xlvi. Predict electronic geometry (arrangement of RHED) xlvii. Determine molecular geometry xlviii. Are bonds polar? xlix. Is the molecule polar? . If dipoles cancel out (the same), it is non polar! . Doesn’t matter about net dipole direction, it will be polar! . Pairs of diploes not arranged to cancel (different sizes)