:16 PM 1 Lewis Structure Tutorial Drawing Lewis Structures Writing Lewis Dot Structures

:16 PM 2 Lewis Structure Tutorial Step #1 Know how to determine the valence electron for all elements. Definition: Valence Electrons An electron in an outer shell of an atom that can participate in forming chemical bonds with other atoms. Example: H has 1 valence electron F has 8 valence electrons Carbon has 4 valence electrons

:16 PM 3 Lewis Structure Tutorial Drawing Lewis Diagrams for Molecules Step 1 Draw each element separately, showing the valence electrons. (Use different symbols for different atoms) Step 2 Choose the least occurring atom as the central atom (or the least electronegative). Except hydrogens or Oxygens. Step 3 Add next frequently occurring atoms around the central atom keeping symmetry in mind. You cannot put two of one atom next to each other Ie/ OOAl must be O Al O Step 4 Add all the electrons and then put Hydrogen on LAST, oxygen atoms on 2 nd to last.

:16 PM 4 Lewis Structure Tutorial Drawing Lewis Diagrams for Molecules Step 5 Never leave an unpaired electron Step 6 Circle your 8’s starting with the central atom Group 1 = 2e- H; Group 2 = 2e- or 4e- :Mg ;Mg;

:16 PM 5 Lewis Structure Tutorial Step #2 (Connectivity) From the Chemical Formula, determine the atom connectivity for the structure. Find the central atom. Examples: i. Given a chemical formula, AB n, A is the central atom and B flanks the A atom. i.e., NH 3, NCl 3, NO 2. In these examples, N is central in the structure. ii. H and F are never central atoms.

:16 PM 6 Lewis Structure Tutorial Valence electrons and number of bonds Step #3 (# of Bond) Determine the number of bonds in the compound Recall the number of bonds at atom prefers depending on the number of valence electrons  X Family # Covalent Bonds* Halogens F, Br, Cl, I Calcogens O, S Nitrogen N, P Carbon C, Si  O N C    1 bond often 2 bond often 3 bond often 4 bond always In general, these are the number of bonds formed by these atoms.

:16 PM 7 Lewis Structure Tutorial Lewis Structure, Octet Rule Guidelines When compounds are formed they tend to follow the Octet Rule. Octet Rule: Atoms will share e - until 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) H prefers 2 e - (electron deficient) iii) :C:N::O::F: 4 u.p3u.p2u.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)

:16 PM 8 Lewis Structure Tutorial Lewis Structure, Octet Rule Guidelines When compounds are formed they tend to follow the Octet Rule. Octet Rule: An atom will gain or loose e - (s) until it is surrounded by eight valence electrons. (Seek a full octet) Rules of the game- i) H prefers 2 e - (electron deficient) i) :C:N::O::F: 4 u.p3u.p2u.p.1u.p. up = unpaired e- 4 bonds3 bonds2 bonds1 bond O=C=ON  NO = OF - F iii) H & F are terminal in the structural formula (Never central)

:16 PM 9 Lewis Structure Tutorial Atomic Connectivity (Bond Capabilities) The atomic arrangement for a molecule is usually given. CH 2 ClF HNO 3 CH 3 COOH H 2 Se H 2 SO 4 O 3 HC F Cl H H N OO O H O S O H O O OO O H C C O H H H O HSe H In general when there is a single central atom in the molecule, CH 2 ClF, SeCl 2, O 3 (CO 2, NH 3, PO 4 3- ), the central atom is the first atom in the chemical formula. Except when the first atom in the chemical formula is Hydrogen (H) or fluorine (F). In which case the central atom is the second atom in the chemical formula. Find the central atom for the following: 1) H 2 Oa) Hb) O2) PCl 3 a) Pb) Cl 3) SO 3 a) Sb) O4) CO 3 2- a) Cb) O 5) BeH 2 a) Beb) H6) IO 3- a) Ib) O

:16 PM 10 Lewis Structure Tutorial Lewis Dot Structure of CO 2 by Bonds Table B. Calculate the number of bonds in compound structure. = (24- 16) = 8 = 4 bonds 22 C. Calculate the remaining electrons to add to structure to complete Lewis dot structure = 8 e - Remaining Total of 16e- in CO 2, of which 8 electrons are used to form 4 bonds and 8 remaining electrons are used to complete Lewis structure. OCO #3. Place the remaining 8 electrons in the structure to complete the Lewis Structure A. Calculate Octet electrons and Total Valence electrons to determine number of bonds #1 Write atom connectivity for CO 2. #2. Draw the four bonds in the structure. OCOOCO CO 2 # of e in its octet # of valence e- 1 C1(8)= 81(4) = 4 2 O2(8)=162(6)=

:16 PM 11 Lewis Structure Tutorial Lewis Dot Structure of ClO 4 - by Bonds Table B. Number of Bonds. # bonds = (40- 32) = 8 = 4 bonds 22 C. Remaining electrons = 24 e - Remaining Writing Lewis Structure: #3. Place the remaining 24 electrons in the structure such that each atom has an octet to complete the Lewis Structure A. Calculate #1. Write atom connectivity for ClO 4 -. #2. Draw the four bonds in the structure. ClO 4 - # of e in its octet # of valence e- 1 Cl1(8)= 81(7) = 7 4 O4(8)=324(6)=24 Charge

:16 PM 12 Lewis Structure Tutorial Lewis Structures: Examples Example a) CH 2 ClF b)SO 2 c)SO 4 2- d) H 3 PO 4 H P O O O O H H

:16 PM 13 Lewis Structure Tutorial Boot elements and the Lewis Dot Structures