Chem 1211 1st Edition Lecture 21 Outline of Last Lecture I Atomic Properties Continued II Chapter 8 Introduction Outline of Current Lecture I Lewis Dot Structures Current Lecture I Lewis Electron Dot Structures a Molecules i Diatomic with the same atoms H H of F F ii Diatomic with different atoms ex H Cl iii Polyatomic water H20 and ammonia NH3 iv Pair electrons a line a bond b ConcepTest How many electrons appear in the correct Lewis dot structure for NH4 i 5 ii 6 iii 7 iv 8 1 ANSWER 8 2 REASOING Nitrogen has 5 electrons and each hydrogen has 1 electron for a total of 9 However since there is a positive charge that means there is one less electron than normal c ConcepTest How many lone pair electrons single bonds double bonds and triple bonds respectively appear in the Lewis structure of HCN i 0 1 0 1 ii 2 1 0 1 iii 0 1 1 0 iv 2 1 1 O v None of these 1 ANSWER B 2 1 0 1 These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute d e f g h i 2 REASONING Lewis structure is H C N a Carbon needs the most electrons so it is in the middle There is a single bond between Hydrogen and Carbon and a triple bond between Carbon and Nitrogen There are two lone electrons Valence e for each element i Anion add 1 eii Cation subtract 1 eCentral atom atom that needs the largest number of e to complete octet i For atoms in the same group the less electronegative never H Rules i Formal charge group bonds unshared e 1 Group valence e in uncombined atom 2 bonds bonding e3 unshared e lone pair electrons ConcepTest What are the formal charges for all the atoms in OCS in this structure O C S i 0 0 0 ii 0 1 0 iii 0 1 1 iv 1 1 1 v None of these 1 ANSWER 0 0 0 2 REASONING Following the formula for formal charges a Oxygen 6 2 4 0 b Carbon 4 4 0 0 c Sulfur 6 2 4 0 ConcepTest How many lone pair electrons on the central atom single bonds double bonds and triple bonds respectively appear in the Lewis structure of PF6 i 0 3 3 0 ii 0 6 0 0 iii 1 3 3 0 iv 1 6 0 0 v 2 6 0 0 1 ANSWER 0 6 0 0 2 REASONING Phosphorus forms a single bond with each of the 6 fluorines a 3rd Row Si P S Cl can have more than 8 electrons ex 10 12 Octet Rule Exceptions i Electron count stable noble gas electron configurations 1 octet rule for most elements 2 2 for H 3 6 for Group 3A B and Al
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