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Drawing Lewis Structures and VSEPR

Drawing Lewis Structures and VSEPR. Draw basic Lewis dot structures of atoms and compounds. Using VSEPR , predict bond shape from electron arrangement in Lewis dot diagram. Additional KEY Terms. OCTET RULE:

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Drawing Lewis Structures and VSEPR

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  1. Drawing Lewis Structures and VSEPR

  2. Draw basic Lewis dot structures of atoms and • compounds. • Using VSEPR, predict bond shape from electron arrangement in Lewis dot diagram. Additional KEY Terms

  3. OCTET RULE: • atoms will gain, lose or share electrons to fill their valence shell (noble gas) • use only valence electrons in Lewis dot.

  4. STEPS / RULES TO LEWIS DOT: • Determine total valence electrons for all atoms. ~Watch for negative/positive/polyatomic ions. • Position least electronegative atom in the centre. • ~central atom usually first in formula (unless H/ F). • CH2ClF, SeCl2, O3 (CO2, NH3, PO43-) • Write other atoms around central with line bond. • ~line represents 2 e- (must be subtracted from total) – Cl Cl – Se

  5. Place electrons around each atom to fill valence. • Too few electrons - give each atom a complete octet by adding double or triple bonds. SeCl2 : 6 +7 + 7 = 20 - 4       – Cl Cl – Se          

  6. Draw the Lewis structure for CO2: CO2 : 4 + 6 + 6 = 16 - 4      –  – – O O – C      

  7. Draw the Lewis structure for SO42- : SO42- : 6 + (4)6 + 2 = 32 - 8 2-                         – O – O O – S – O

  8. BeCl2: 2 + 7 + 7 = 16 - 4 Ionic Bond – Cl Cl – Be +2 -1 -1                             Cl Cl Be

  9. VSEPR Valence Shell Electron Pair Repulsion Theory • Predicts 3D structures of molecules. • Shape calculated by comparing bonding and lone • pairelectrons around the central atom. • Minimizes the electrostatic repulsion between • electrons in valence sublevels.

  10. AXE method: A: Central atom Xn: # of bonding pairs En: # lone pairs

  11. Central Atom with only bonding pairs: Draw the Lewis structure for BF3: BF3 : 3 + (3)7 = 24 - 6 *Unusual (Does not have octet)                   3 – bonding pairs (X3) 0 – lone pairs – F F – B – F Trigonal Planar– 120obond angle

  12. Draw the Lewis structure for CH4: 4 – bonding pairs (X4) 0 – lone pairs Tetrahedral – 109.5o Draw the Lewis structure for PCl5: 5 – bonding pairs (X5) 0 – lone pairs Trigonal Bipyramidal – 90o and 120o Draw the Lewis structure for SF6: 6 – bonding pairs (X6) 0 – lone pairs Octahedral – 90o

  13. Central Atom with LONE pairs: Lone pairs have a greater repulsion force and distort the predicted bond angles. H2S : 1 + 1 + 6 = 8 - 4 *Predict Linear   H – – H S   2 – bonding pairs (X2) 2 – lone pairs (E2) Bent – 104.5obond angle

  14. Draw the Lewis structure for PF3: PF3 : 5 + (3)7 = 26 - 6 *Predict Trigonal Planar                     3 – bonding pairs (X3) 1 – lone pairs – F F – P – F Trigonal Pyramidal – 107o

  15. Treat double/triple bonds as single bonds: CO2: 4 + 6 + 6 = 16 - 4     – –  Double Bonds  O – – O C       2 – bonding pairs (X2) 0 – lone pairs Linear – 180obond angle

  16. CAN YOU / HAVE YOU? • Draw basic Lewis dot structures of atoms and • compounds. • Using VSEPR, predict bond shape from electron arrangement in Lewis dot diagram. Additional KEY Terms

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