5. CONNECT THE DOTS between atoms. 2 e- = a bond, denoted by a line ( : = -)

Transcription

1 LEWIS STRUCTURES CLIFF NOTES Name: The gal f the Lewis structure is t have all atms get an ctet after the structure is cmplete! (H nly wants 2 e- and B wants 6) 1. Write the chemical frmula, and cunt the ttal # f valence electrns. This is the amunt f electrns allwed in the Lewis Structure These electrns can be placed anywhere in the structure and dn t belng t any specific atm 2. Arrange the atms arund each ther. Hints: a) The least electrnegative atm typically ges in the center - usually C b) Hydrgen is terminal (at the end b/c it nly can frm 1 bnd) 3. Put in electrns (dts) arund the atms t satisfy the ctet f all the atms 4. Check t see that yu have the same # e - s as in step 1, if nt, rearrange the # e - s and/r atms. 5. CONNECT THE DOTS between atms. 2 e- = a bnd, dented by a line ( : = -) Guided practice prblems: carbn mnxide CH 2 O

2 Lewis Structures Practice Wrksheet 1 Draw the Lewis structures fr the fllwing: a) Nitrgen trifluride b) Methane c) Flurine d) xygen e) Water f) Sulfur dichlride g) Phsphrus pentachlride h) Methyl Alchl (CH 3 OH)

3 Mre detailed infrmatin DRAWING LEWIS STRUCTURES Start by learning this basic step-by-step prcedure fr drawing Lewis structures. 1. Draw a skeletn structure. A skeletn structure is a rugh map shwing the arrangement f atms within the mlecule. In general, yu need t determine the skeletn experimentally, but here are a few guidelines fr predicting skeletn structures frm mlecular frmulas. Central atms are usually the largest atms, r the least electrnegative atm. H and the halgens are usually utside atms. Dn't put mre than fur atms arund a central atm unless the central atm is third perid r lwer. 2. Cunt ttal valence electrns. Add the number f electrns in the valence shells f all atms in the mlecule. If the mlecule is charged, add an electrn fr each negative charge and subtract an electrn fr each psitive charge. Nble gas cmpunds are very uncmmn (except n general chemistry tests!) Shuld yu encunter ne, each nble gas atm has 8 valence electrns. 3. Cnnect the structure. Draw a bnd between the central atm and each utside atm. Each bnd uses 2 valence electrns. 4. Place electrns n utside atms. Use remaining electrns t satisfy the ctets fr each f the utside atms. If yu run ut f electrns at this pint, the skeletn structure was wrng. G back t step I. 5. Place all remaining electrns n the central atm. If there are mre than 8 electrns n the central atm, and the central atm is nt third perid r lwer, yu cunted the number f valence electrns incrrectly. G back t step II. If the ctet n the central atm is nt cmplete, try sharing lne pairs f utside atms t frm duble r triple bnds. Write ne multiply bund structure fr each utside atm with a lne pair t share; these are resnance structures. If yu can't get an ctet n the central atm, at this pint, check t see whether the ttal number f valence electrns fr this mlecule is dd. It's impssible t give ctets t all atms in an dd electrn mlecules. Get as clse t an ctet as pssible by frming multiple bnds. Authr: Fred Senese senese@antine.frstburg.edu

4 Lewis Structures Practice Wrksheet 2 Draw the best Lewis structures fr the fllwing mlecules r ins: a) Phsphrus tribrmide f) xygen b) (Diazine) Dinitrgen dihydride g) nitrgen c) Methanl CH 3 OH h) frmaldehyde CH 2 O d) Nitrite in i) nitrite in (draw differently than letter d) e) Ethene C 2 H 4 j) Acetylene C 2 H 2

5 Lewis Structures Practice Wrksheet 3 Draw the best Lewis structures fr the fllwing mlecules r ins: k) SBF (keep brn central) p) brmine l) HBr q) idine m) C 2 H 5 OH (ethanl) r) flurine n) dinitrgen tetrafluride s) What d yu ntice abut the frmulas f the elements f hydrgen, nitrgen, xygen, flurine, chlrine, brmine and idine? ) sulfur hexafluride t) carbn dixide

6 Resnance Structures Practice

7 Draw all f the pssible resnance structures fr the fllwing ins r mlecules: 1) nitrate in: 2) frmate in (CHO 2-1 ): 3) cyclbutadiene (C 4 H 4 ): 4) zne (O 3 ):