1 / 25

Chapter 8: Basic Concepts of Chemical Bonding

Chapter 8: Basic Concepts of Chemical Bonding. Chapter 8: Basic Concepts of Chemical Bonding. Chemical Bonds. ionic bond. electrons are transferred from one atom to another atom. covalent bond. electrons are shared between two atoms. metallic bond.

Download Presentation

Chapter 8: Basic Concepts of Chemical Bonding

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. Chapter 8: Basic Concepts of Chemical Bonding

  2. Chapter 8: Basic Concepts of Chemical Bonding Chemical Bonds • ionic bond electrons are transferred from one atom to another atom • covalent bond electrons are shared between two atoms • metallic bond electrons are free to move between all atoms

  3. Chapter 8: Basic Concepts of Chemical Bonding The formation of chemical bonds involves valence electrons Lewis Symbols: “shorthand” for showing valence electrons Gilbert Lewis (1875-1946)

  4. 1A 8A 2A 3A 4A 5A 6A 7A Chapter 8: Basic Concepts of Chemical Bonding Lewis dot structures: He H Li Be B C N O F Ne Na Mg Al Si P S Cl Ar For representative (main group) elements: group number = number of valence electrons

  5. K Cl Cl Chapter 8: Basic Concepts of Chemical Bonding Noble gases, except helium, have 8valence electrons ns2np6 Octet Rule: When atoms react, they tend to lose, gain, or share the number of electrons required to achieve eight valence electrons (an “octet” of electrons) + K+ + [Ar] [Ar] electron configuration:

  6. Chapter 8: Basic Concepts of Chemical Bonding Formation of an ionic lattice Cl- Na+ Cl- Na+ Cl- Na+

  7. Chapter 8: Basic Concepts of Chemical Bonding very exothermic DH<0 + Cl- (g) Na+ (s) NaCl (s)

  8. Chapter 8: Basic Concepts of Chemical Bonding charge on ions distance between charges Strength of ionic bond depends on Eel • the larger Eel, the stronger the bond • the greater the charges, the stronger the bond • the smaller the distance between the charges, the stronger the bond

  9. Chapter 8: Basic Concepts of Chemical Bonding The stronger the ionic bond the the melting point higher 1261oC 66, 133 2852oC 66, 140 SrI2 +2, -1 538°C 113, 220 r1 r2

  10. H H F F Chapter 8: Basic Concepts of Chemical Bondingc Covalent Bonds … … are formed when two atoms share electrons … in order to achieve “noble gas configuration” … of the nearest noble gas Each hydrogen has the electron configuration of He + H H Each fluorine has the electron configuration of Ne + F F

  11. F F Chapter 8: Basic Concepts of Chemical Bonding Covalent Bonds + H H H H H H F F + F F • A shared electron pair is drawn as a dash (two electrons!) • Unshared electrons are drawn as dots

  12. Triple bond Single bond Double bond C + O + O or O C O O C O or + N N N N N N Chapter 8: Basic Concepts of Chemical Bonding Single and Multiple Bonds F F + F F F F or

  13. Distance between atoms (bond length) decreases Chapter 8: Basic Concepts of Chemical Bonding Single and Multiple Bonds X X Bond strength increases X X X X

  14. Cl Cl Chapter 8: Basic Concepts of Chemical Bonding Bond Polarity and Electronegativity • When both atoms attract bond electrons equally, electrons are shared equally non-polar covalent bond: equal sharing of electrons

  15. H Cl Chapter 8: Basic Concepts of Chemical Bonding Bond Polarity and Electronegativity • If one of the atoms attracts bond electrons more strongly, electrons are shared unequally +  - polar covalent bond: unequal sharing of electrons

  16. H Cl - Na+ Cl Chapter 8: Basic Concepts of Chemical Bonding Bond Polarity and Electronegativity For comparison: +  - polar covalent bond: unequal sharing of electrons ionic bond: electrons are not shared

  17. Chapter 8: Basic Concepts of Chemical Bonding How do we know when a non-polar, polar, or ionic bond is formed? The tendency of atom to attract electrons when forming a molecule is summarized in the concept of electronegativity Increase in Electronegativity

  18. Chapter 8: Basic Concepts of Chemical Bonding How do we know when a non-polar, polar, or ionic bond is formed? If the difference in Electronegativity, DEN, is… …smaller than 0.5 DEN < 0.5 => nonpolar bond …greater than or equal to 0.5 AND smaller than 2.0 0.5 DEN < 2.0 => polar bond …greater than or equal to 2.0 DEN  2.0 => ionic bond

  19. S Chapter 8: Basic Concepts of Chemical Bonding Among the following examples, which bond is most polar? all equally non-polar C-F (C-H is non-polar) P-Cl (furthest apart in P.T. => largest DEN) all equally non-polar O-I (furthest apart in P.T. => largest DEN) e) O-I O-N O-F

  20. S C C Chapter 8: Basic Concepts of Chemical Bonding Among the following examples, which bond is shortest? H-H C-H Cl-Cl Bond length depends on (a) radii of the bonded atoms remember that the atomic radii decrease along a period in the P.T. (b) the number of bonds between atoms

  21. Chapter 8: Basic Concepts of Chemical Bonding Drawing Lewis Structures of Molecules there are no Lewis structures for ionic compounds!! • If the compound contains more than 2 atoms: • how are the atoms bonded and, • if there are nonbonding electron, where are they?

  22. Chapter 8: Basic Concepts of Chemical Bonding Molecules with a central atom : NH3, PCl3, CHCl3 central atom is generally the first in the molecular formula

  23. H2O Chapter 8: Basic Concepts of Chemical Bonding …unless the first element is Hydrogen : H has only one valence electron => can only make one bond HCN (same order as in formula)

  24. Chapter 8: Basic Concepts of Chemical Bonding Rules for Drawing Lewis Structures (1) sum valence electrons from all atoms: these are the ones that need to be distributed 8 NH3 (2) connect atoms by covalent bonds: count electrons used up 6 (3) complete "octets" of atomsbound to central atom n/a (4) place any leftovers from (1) on the central atom check that central atom has octet + 2 (5) If there are not enough electrons to give the central atom an octet, try multiple bonds n/a

  25. Chapter 8: Basic Concepts of Chemical Bonding (1) sum valence electrons from all atoms: these are the ones that need to be distributed 10 CO (2) connect atoms by covalent bonds: count electrons used up 2 (3) complete "octets" of atomsbound to central atom C O + 6 (4) place any leftovers from (1) on the central atom check that central atom has octet C O + 2 (5) If there are not enough electrons to give the central atom an octet, try multiple bonds triple bond!

More Related