1 / 39

Formal Charges

Formal Charges. Formal charge is the charge calculated for an atom in a Lewis structure on the basis of an equal sharing of bonded electron pairs. :. O. N. H. O. :. :. O. Nitric acid. Formal charge of H. We will calculate the formal charge for each atom in this Lewis structure. :. O.

esben
Download Presentation

Formal Charges

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Formal Charges Dr Seemal Jelani

  2. Formal charge is the charge calculated for an atom in a Lewis structure on the basis of an equal sharing of bonded electron pairs. Dr Seemal Jelani

  3. .. : O .. N H O .. : : O Nitric acid Formal charge of H • We will calculate the formal charge for each atom in this Lewis structure. .. Dr Seemal Jelani

  4. .. : O .. N H O .. : : O Nitric acid Formal charge of H • Hydrogen shares 2 electrons with oxygen. • Assign 1 electron to H and 1 to O. • A neutral hydrogen atom has 1 electron. • Therefore, the formal charge of H in nitric acid is 0. .. Dr Seemal Jelani

  5. .. : O .. N H O .. : : O Nitric acid Formal charge of O • Oxygen has 4 electrons in covalent bonds. • Assign 2 of these 4 electrons to O. • Oxygen has 2 unshared pairs. Assign all 4 of these electrons to O. • Therefore, the total number of electrons assigned to O is 2 + 4 = 6. .. Dr Seemal Jelani

  6. .. : O .. N H O .. : : O Nitric acid Formal charge of O • Electron count of O is 6. • A neutral oxygen has 6 electrons. • Therefore, the formal charge of O is 0. .. Dr Seemal Jelani

  7. .. : O .. N H O .. : : O Nitric acid Formal charge of O • Electron count of O is 6 (4 electrons from unshared pairs + half of 4 bonded electrons). • A neutral oxygen has 6 electrons. • Therefore, the formal charge of O is 0. .. Dr Seemal Jelani

  8. .. : O .. N H O .. : : O Nitric acid Formal charge of O • Electron count of O is 7 (6 electrons from unshared pairs + half of 2 bonded electrons). • A neutral oxygen has 6 electrons. • Therefore, the formal charge of O is -1. .. Dr Seemal Jelani

  9. .. : O .. N H O .. : : O Nitric acid Formal charge of N • Electron count of N is 4 (half of 8 electrons in covalent bonds). • A neutral nitrogen has 5 electrons. • Therefore, the formal charge of N is +1. – .. Dr Seemal Jelani

  10. .. : O .. N H O .. : : O Nitric acid Formal charges • A Lewis structure is not complete unless formal charges (if any) are shown. + – .. Dr Seemal Jelani

  11. Formal Charge An arithmetic formula for calculating formal charge. Formal charge = group numberin periodic table number ofbonds number ofunshared electrons – – Dr Seemal Jelani

  12. .. 1 H : : F + .. .. : : N B F F H H .. .. : : F H .. 4 "Electron counts" and formal charges in NH4+ and BF4- 7 – 4 Dr Seemal Jelani

  13. Dr Seemal Jelani Chem-241 Hydronium ion assigned 5 valence electrons .. +Formal charge of +1 H O H H 6-(2+3) 6-5 + 1

  14. Dr Seemal Jelani Chem-241 • Bicarbonate assigned 7 valence electrons: Ö: - charge of -1 H Ö C- Ö: ¨ ¨ 6-(6+1) 6-7 -1

  15. Condensed structural formulas Dr Seemal Jelani

  16. H H H C H C C H : H : H O (CH3)2CHOH or CH3CHCH3 H OH Condensed structural formulas • Lewis structures in which many (or all) covalent bonds and electron pairs are omitted. can be condensed to: Dr Seemal Jelani

  17. CH3CH2CH2CH3 is shown as CH3CH2CH2CH2OHis shown as OH Bond-line formulas • Omit atom symbols. Represent structure by showing bonds between carbons and atoms other than hydrogen. • Atoms other than carbon and hydrogen are called heteroatoms. Dr Seemal Jelani

  18. H Cl Cl C H2C CH2 H2C CH2 C H H Bond-line formulas • Omit atom symbols. Represent structure by showing bonds between carbons and atoms other than hydrogen. • Atoms other than carbon and hydrogen are called heteroatoms. is shown as Dr Seemal Jelani

  19. Constitutional Isomers Dr Seemal Jelani

  20. Constitutional isomers • Isomers are different compounds that have the same molecular formula. • Constitutional isomers are isomers that differ in the order in which the atoms are connected. • An older term for constitutional isomers is “structural isomers.” Dr Seemal Jelani

  21. O H2NCNH2 A Historical Note NH4OCN Urea Ammonium cyanate • In 1823 Friedrich Wöhler discovered that when ammonium cyanate was dissolved in hot water, it was converted to urea. • Ammonium cyanate and urea are constitutional isomers of CH4N2O. • Ammonium cyanate is “inorganic.” Urea is “organic.” Wöhler is credited with an important early contribution that helped overturn the theory of “vitalism.” Dr Seemal Jelani

  22. H .. .. : H C O N O .. .. H Examples of constitutional isomers .. • Both have the molecular formula CH3NO2 but the atoms are connected in a different order. H : O + N H C – : : O H .. Nitromethane Methyl nitrite Dr Seemal Jelani

  23. Dr Seemal Jelani Shapes

  24. Dr Seemal Jelani

  25. Methane • tetrahedral geometry • H—C—H angle = 109.5° Dr Seemal Jelani

  26. Methane • tetrahedral geometry • each H—C—H angle = 109.5° Dr Seemal Jelani

  27. Valence Shell Electron Pair Repulsions • The most stable arrangement of groups attached to a central atom is the one that has the maximum separation of electron pairs(bonded or nonbonded). Dr Seemal Jelani

  28. Water • bent geometry • H—O—H angle = 105° H H : O .. but notice the tetrahedral arrangement of electron pairs Dr Seemal Jelani

  29. Ammonia • trigonal pyramidal geometry • H—N—H angle = 107° H H : N H but notice the tetrahedral arrangement of electron pairs Dr Seemal Jelani

  30. Boron Trifluoride • F—B—F angle = 120° • trigonal planar geometry allows for maximum separationof three electron pairs Dr Seemal Jelani

  31. H O C H Formaldehyde: CH2=O • H—C—H and H—C—Oangles are close to 120° • trigonal planar geometry Dr Seemal Jelani

  32. O O C Figure 1.12: Carbon Dioxide • O—C—O angle = 180° • linear geometry Dr Seemal Jelani

  33. Polar Covalent Bondsand Electronegativity Dr Seemal Jelani

  34. Electronegativity is a measure of an element to attract electrons toward itself when bonded to another element. • An electronegative element attracts electrons. • An electropositive element releases electrons. Dr Seemal Jelani

  35. Pauling Electronegativity Scale Dr Seemal Jelani

  36. Electronegativity increases • from left to right in the periodic table • Electronegativity decreases going down a group. Dr Seemal Jelani

  37. Dr Seemal Jelani

  38. Generalization .. .. : : : : N N F F .. .. H—H Nonpolar bonds connect atoms of the same electronegativity Dr Seemal Jelani

  39. d- .. .. d- d+ d+ d+ : H H O H F .. .. Generalization • The greater the difference in electronegativitybetween two bonded atoms; the more polar the bond. d+ d- d- : : C O O .. .. polar bonds connect atoms ofdifferent electronegativity Dr Seemal Jelani

More Related