CHM 115 Lecture 11 Reading was: KTT: Sections 8.2, 8.4 - 8.6 Lecture 12: Section 8.9 Lecture 13: Section 8.6 * Lewis Electron-dot Structures Number of dots = number of outer (valence) electrons Leave a maximum number unpaired. This is NOT the arrangement in some isolated atoms Rules: Depicting Valence Electrons in Main Group Atoms * Non-metals (Groups 6A and 7A) Metals (Groups 1A and 2A) ? Li ? Mg ? Li+ Mg2+ [He]2s1 [He] [Ne]3s2 [Ne] [He]2s22p5 [He]2s22p6 = [Ne] [Ne]3s23p4 [Ne]3s23p6 = [Ar] Closed Shells Most atoms possess filled outer shells when bonded. In Ionic Compounds: : : : . F : . : . S : : : : F ? : : : : S 2? * Ionic Bonding A tendency to form closed shells is observed during electron transfer Na [Ne] 3s1 + Cl [Ne] 3s2 3p5 Na+ [Ne] + Cl- [Ar] Na Cl Na + Cl ? ? ? ? ? ? ? ? - ? ? ? ? ? ? ? ? + or, in terms of Lewis electron dots * Buddy Question #1 Let?s see what you remember about bonds between atoms. Covalent bonds can form when? electrons are transferred from one atom to another. electrons are shared between two atoms. electrons are shared among all the atoms in a solid. * Bonding Ionic Bonding: Attraction of positive and negative ions. Covalent Bonding: Usually, the sharing of pairs of electrons among atoms in a molecule or polyatomic ion or covalent network solid. Metallic Bonding: Conducting electrons distributed over many atomic nuclei. * Electron Sharing Transferring electrons creates closed shells in ionic compounds: Sharing electrons creates closed shells in most covalent compounds: Closed shells Bonding pairs Non-bonding electrons Lone pairs * Buddy Question #2 Which compound contains both ionic and covalent bonds? MgCl2 Na2SO4 CH4 * Buddy Question #2 Which compound contains both ionic and covalent bonds? MgCl2 Mg2+ and two Cl- ions Na2SO4 two Na+ ions and one SO42- ion all four S-O bonds are covalent CH4 all four C-H bonds are covalent * Lewis Structures Lewis structures indicate: the atoms in a molecule or covalent ion how atoms are arranged the location and type of bonds the location of lone pairs * Buddy Question #3 How many valence electrons are found in CH3Cl ? * Drawing Lewis Structures Count the number of valence electrons CH3Cl Valence electrons C = 4 3H = 3 Cl = 7 14 valence e- * Drawing Lewis Structures Draw single bonds from central atom to surrounding atoms. * Drawing Lewis Structures Count remaining valence electrons. Distribute to fill octets. 14 electrons - 8 in bonds = 6 electrons * Drawing Lewis Structures Draw the Lewis Structure for HOBr. * Multiple Bonds Sometimes pairs of atoms can gain an even greater energy Advantage by sharing more than one pair of electrons Bond Order: the number of pairs of electrons that are shared between two atoms. * Drawing Lewis Structures C2H4 Multiple bonds * Drawing Lewis Structures Draw the Lewis Structure for ClNO
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