Lewis Structure Discussion PDF

LEWIS STRUCTURE LEWIS STRUCTURE  is a simplified representation of the valence shell electrons in a molecule. It is used to show how the electrons are arranged around individual atoms in a molecule. Electrons are shown as “dots” or for bonding electrons as a “line” between th...

LEWIS STRUCTURE LEWIS STRUCTURE  is a simplified representation of the valence shell electrons in a molecule. It is used to show how the electrons are arranged around individual atoms in a molecule. Electrons are shown as “dots” or for bonding electrons as a “line” between the two atoms.  Lewis Structure by Bond Determination 1. Know how to determine the valence electrons for all elements. 2. (Connectivity) From the chemical formula, determine the atom connectivity for the structure. i. Given a chemical formula, ABn, A is the central atom and B flanks the A atom. i.e., NH3, NCl3, NO2. In these examples, N is central in the structure. ii. H and F are never central atoms. 3. (# of electrons in Bonding) Determine the number of bonds in the compound, by calculating the theoretical Octet electrons (Oe) minus the total valence electrons (TVe) and dividing by 2 (2 electrons = 1 bond). Oe 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.  Lewis Structure by Bond Determination 4. (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 the 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. Valence electrons for Elements Recall that the valence electrons for the elements can be determined based on the elements position on the periodic table. Lewis Dot Symbol Valence electrons and number of bonds Number of bonds elements prefers depending on the number of valence electrons. In general : Fam ily → # C o v a l e n t B o n d s* → H a lo g e n s X 1 bond often F , B r, C l, I C a lc o g e n s O, S O → 2 bond often N it r o g e n N, P N → 3 bond often C a rb o n C , Si C → 4 bond always The above chart is a guide on the number of bonds formed by these atoms. Lewis Structure, Octet Rule Guidelines When compounds are formed they tend to follow the Octet Rule. Octet Rule: Atoms will share electrons (e-) until it is surrounded by eight valence electrons.  Atomic Connectivity The atomic arrangement for a molecule is usually given. CH2ClF H2Se O3 Cl F H O O O H C H Se H In general when there is a single central atom in the molecule, CH2ClF, O3 (CO2, NH3, PO43-), 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. Example 1: Identify the central atom for the following: 1) H2O 2) PCl3 3) SO3 4) CO32- 5) BeH2 6) IO3- Setting up Bond Table: Setting up the bond table requires the chemical formula, and determining the number of electrons around each atom. A) Chemical Formula I.e., HNO3 B) Oe - Octet Electrons. This is always either 8 or 2 (for H) C) Tve - Total Valence Electron. ChemFormula Octet e- Tot Val e- HNO3 Oe Tve H 1x2=2 1x1=1 N 1x8=8 1x5=5 O 3 x 8 = 24 3 x 6 = 18 34 24 Note this works only if the chemical specie obeys the octet rule. For chemical specie which violates the octet rule, this method must be modified.  Calculating the Number of Bonds and the Remaining electrons After setting up the bond table, calculate the number of bonds in the chemical specie and the number of electrons. The remaining electrons are place around the atoms in the chemical specie such that each atom obeys the octet rule HNO3 Oe Tve # Bonding e- Bond Table 34 - 24 = 10 # of Bonds 10/2 = 5 Remaining e- Tve(24) - electrons in Bond (10) = 14  Putting it Together: 1) Chemical formula: 2) Atomic sequence: HNO3 O N O O H 3) Number of bonds =5 4) Remaining electrons = 14 5) Lewis Structure with 5 bonds: O N O 6) Complete Lewis Structure with 14 remaining electrons O O N O H O H  Lewis Dot Structure of CO2 by Bonds Table A. Calculate Octet electrons (Oe-) and B. Calculate the number of bonds in compound Total Valence electrons to determine structure. number of bonds # bonds = (Oe - TVe) 2 CO2 Oe TVe 1C 1 (8)= 8 1 (4) = 4 = (24- 16) = 8 = 4 bonds 2 2 2O 2 (8)=16 2 (6)=12 Chg C. Calculate the remaining electrons to add to structure to complete Lewis dot structure. 24 16 Remaining e- = TVe - e- used in bonding. = 16 - 8 = 8 e-Remaining Writing Lewis Structure: First determine atom connectivity keeping in mind that H and F can never be central atoms. Generally when given the formula, ABn, A is the central atom in the structure (but not always), and B atoms flank the central atom. Next use information from the above calculations. Total of 16e- in CO2, of which 8 electrons are used to form 4 bonds and 8 remaining electrons are used to complete Lewis structure. O C O O C O O C O 1,2. Write atom 3,4,5. Draw the four 6. Place the remaining 8 electrons in the connectivity for CO2. bonds in the structure. structure to complete the Lewis Structure  Lewis Dot Structure of ClO4- by Bonds Table A. Calculate (Oe-) and (TVe) B. Number of Bonds. ClO4- Oe TVe # bonds = (40- 32) = 8 = 4 bonds 2 2 1 Cl 1 (8)= 8 1 (7) = 7 C. Remaining electrons. 4O 4 (8)= 32 4 (6)= 24 Remaining e- = 32 - 8 = 24 e-Remaining Chg 1 40 32 Writing Lewis Structure: 6. Place the remaining 24 electrons 1,2. Write atom 3.4.5. Draw the in the structure such that each atom connectivity for ClO4-. four bonds in the has an octet to complete the Lewis structure. Structure O O O O Cl O O Cl O O Cl O O O O  Example 2: Construct the lewis structure of the following: 1. CH2ClF 2. SO42- 3. H3PO4