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Lewis Structure Tutorial

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7 pages
Drawing Lewis Structures
A Tutorial on Writing Lewis Dot Structure
Dr. Fred Omega Garces
Chemistry 100
Miramar College
Lewis Structure Tutorial1 10.7.00 6:16 PM
Lewis Structure by Bond Determination
1. Know how to determine the valence electron for all elements.
2. (Connectivity) From the Chemical Formula, determine the atom
connectivity for the structure.
i. Given a chemical formula, AB , A is the central atom and B flanks the A atom.n
i.e., NH , NCl , NO . In these examples, N is central in the structure.3 3 2
ii. H and F are never central atoms.
2. (# of Bond) Determine the number of bonds in the compound, by
calculating the theoretical Octet electrons (Oe) minus the total valence
electrons (TVe). O-e is the theoretical number of electrons necessary for each
atom in the structure to obtain a Noble Gas electron configuration, while TVe is the
actual number of total valence electron for each atom in the structure.
3. (Remaining e-) Calculate the number of remaining electrons in the
compound by taking the total valence electron (TVe) minus the number of
electrons that was used to form bonds.
Complete Lewis structure by drawing atomic connectivity. Write
bonds in the structure and the place remaining electrons to selected
atoms in the structure to give each atom an octet. Keep in mind
that the H-atom is satisfied with 2 electrons.
2 Lewis Structure Tutorial 10.7.00 6:16 PM Valence electrons for Elements
Recall how to determine the valence electron for the ...
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Drawing Lewis Structures A Tutorial on Writing Lewis Dot Structure
Dr. Fred Omega Garces Chemistry 100 Miramar College
Lewis Structure Tutorial
10.7.00 6:M
Lewis Structure by Bond Determination 1. Knowhow to determine thevalence electronfor all elements. 2. (Connectivity) From the Chemical Formula, determine the atom connectivity for the structure. i. Givena chemical formula,AB, A is the central atom andBflanks theAatom. n i.e.,NH ,NCl ,NIn these examples,O .Nis central in the structure. 3 32 ii. Hand F are never central atoms. 2. (# of Bond) Determine the number of bonds in the compound, by calculating the theoretical Octet electrons (Oe) minus the total valence electrons (TVe). O-eis the theoretical number of electrons necessary for each atom in the structure to obtain a Noble Gas electron configuration, while TVeis the actual number of total valence electron for each atomin the structure. 3. (Remaining e-) Calculate the number of remaining electrons in the compound by taking the total valence electron (TVe) minus the number of electrons that was used to form bonds.
Complete Lewis structure by drawing atomic connectivity.Write bonds in the structure and the place remaining electrons to selected atoms in the structure to give each atom an octet.Keep in mind that the H-atom is satisfied with 2 electrons.
Lewis Structure Tutorial
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Valence electrons for Elements
Recall how to determine the valence electron for the elements based on the elements position on the periodic table.
Lewis Dot Symbol
Lewis Structure Tutorial
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Valence electrons and number of bonds Recall the number of bonds at atom prefers depending on the number of valence electrons Family #Covalent Bonds*
Halogens X F, Br, Cl, I1 bond often Calcogens O2 bondoften O, S Nitrogen 3 bondoften N N, P Carbon C4 bondalways C, Si In general, these are the number ofbonds formed by these atoms. 4Lewis Structure Tutorial 10.7.00 6:M
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Lewis Structure, Octet Rule Guidelines
When compounds are formed they tend to follow theOctet Rule. -Octet Rule:Atoms will share euntil it is surrounded by eight valence electrons. Rules of the game-i) O.R.works mostly for second period elements. Many exceptions especially with 3rd period elements (d-orbitals) -ii) Hprefers 2 e(electron deficient) . ... . iii):O: :F::C: N: . .. 4 u.p3u.p 2u.p.1u.p. up= unpaired e-4 bonds3 bonds2 bonds1 bond  O=C=ON NO = OF - F iv) H& F are terminal in the structural formula (Never central)
Lewis Structure Tutorial
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Atomic Connectivity The atomic arrangement for a molecule is usually given. CH ClFHNOCH COOHH SeH SOO 23322 43 Cl O N OHO O H Se HO O O H C F O HO H  CCH OS H H O H H O In general when there is a single central atom in the molecule,CH ClF,SeCl , O 2 23 3-(CO ,NH ,Pthe central atom is the first atom in the chemical formula.O ), 2 34 Except when the first atom in the chemical formula is Hydrogen (H) or fluorine (F). Inwhich case the central atom is the second atom in the chemical formula.
Find the central atom for the following: 1) H Oa) Hb) O2) PCla) P 2 3 2-3) SOa) Sb) O4) COa) C 3 3 3-5) BeHa) Beb) H6) IOa) I 2
Lewis Structure Tutorial
b) Cl b) O b) O
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Setting up Bond Table Setting up the bond table requires the chemical formula, and determining the number of electrons around each atom. A) Chemical FormulaI.e.,HNO 3 B) Oe - Octet Electrons (This is always either 8 (or 2 for H) C) Tve - Total Valence Electron. ChemFormula Octete- TotVal e-HNO OeTve 3 1 x 2 = 21 x 1 = 1 H 1 x 8 = 81 x 5 = 5 N O3 x 6 = 183 x 8 = 24 34 24
Note this receipt works only if the chemical specie obeys the octet rule.For chemical specie which violates the octet rule, this method must be modified. 7Lewis Structure Tutorial10.7.00 6:M
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Calculating the Number of Bonds and the Remaining electrons After setting up the bond table, calculate thenumber of bondsin the chemical specie and the number of electrons. Theremaining electronsare place around the atoms in the chemical specie such that each atom obeys the octet rule
HNO 3 Bond Table # of Bonds -Remaining e
-Oe Tve# Bonding e 34 -24 =10 10/2 =5 Tve(24) - electrons in Bond (10) =14
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Putting it Together 1) Chemical formula:2) Atomic sequence: HNO 3 ONO O 3) Number of bonds= 5H 4) Remaining electrons= 14
5) Lewis Structure with 5 bonds:  6)Complete Lewis Structure ONO with14remaining electrons O ONO H O H Lewis Structure TutorialM 10.7.00 6:
Lewis Dot Structure of COby Bonds Table 2 A. Calculate Octet electrons (Oe-) and B. Calculate the number of bonds in compound structure. Total Valence electrons to determine number of bonds # bonds- TVe)= (Oe 2 CO OeTVe 2  =(24- 16)= 8=4 bonds 1 C1¥(8)= 81¥(4) = 4  22 2 O2¥(8)=16 2¥(6)=12 C. Calculatethe remaining electrons to add to Chg structure to complete Lewis dot structure. 24 16-Remaining e-=TVe - e usedin bonding. - ==16 - 88 e Remaining Writing Lewis Structure: First determine atom connectivity keeping in mind that H and F can never be central atoms. Generallywhen given the formula, ABn, A is the central atom in the structure (but not always), and B atoms flank the central atom.Next use informationfrom the above calculations.Total of 16e- in CO , of which 8 electrons are used to form 4 bonds 2 and 8 remaining electrons are used to complete Lewis structure.
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O C O 1,2. Write atom connectivity for CO . 2
O C O 3,4,5. Draw the four bonds in the structure.
O C O 6. Place the remaining 8 electrons in the structure to complete the Lewis Structure
Lewis Structure Tutorial
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-Lewis Dot Structure of ClOby Bonds Table 4
A. Calculate (Oe-) and (TVe)
-ClO 4 1 Cl 4 O Chg
Oe 1¥(8)= 8 4¥(8)= 32 40
TVe 1¥(7) = 7 4¥(6)= 24 1 32
Writing Lewis Structure:
B. Number ofBonds. # bonds== 8= (40- 32)4 bonds  22
C. Remainingelectrons. -Remaining e-= 32 - 8=24 e Remaining
6. Place the remaining 24electrons 3.4.5. Draw the 1,2. Write atom in the structure such that each atom four bonds in the -. connectivity for ClO has an octetto complete the Lewis 4 structure. Structure O OO O Cl O O ClO O ClO O O O 11Lewis Structure TutorialM10.7.00 6:
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Lewis Structures:Examples Example
a) CHClF 2Cl H CF H
2-c) SO 4 O O S O O
b)SO 2 O SO
d) HPO 3 4 O O PO H H O H
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Summary Lewis Structure Determination: ¥Molecular Formula ¥(H and F are terminal)Atomic Sequence ¥Determine the # of bonds - -Oe andTVe -# of Bonds = (Oe - TVe ) / 2 ¥Determine remaining electrons - -Re = (TVe )- (#e inbonding) ¥Make sure all atoms satisfy octet rule (Except H which is satisfied with 2 electrons)
Lewis Structure Tutorial
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