1. Chemical Bonding What holds things together? PGCC CHM 101 Sinex

2. Chlorides of Period 2 compound LiClBeCl 2 BCl 3 CCl 4 NCl 3 OCl 2 Cl 2 melting point 610415-107-23-40-121-102 Chlorides of Period 3 compound NaClMgCl 2 AlCl 3 SiCl 4 PCl 3 SCl 6 Cl 2 melting point 801714193-69-112-51-102 Let’s examine the melting point of compounds across two periods. What is the trend? lowhigh Conductivity - highConductivity - low CRC Handbook of Chemistry and Physics, 1995

3. Bonding Can we explain the melting point behavior across a period? involves the valence electrons or outermost shell (or highest shell) electrons for group A elements - the group number tells how many valence electrons How many valence electrons on N? Group 5A – 5 valence electrons

4. Bonding… Lewis dot structures show the valence electrons around at atom and for most molecules and compounds a complete octet for the elements most monatomic ions have an electron configuration of noble gases N Al F + e -  F 1s 2 2s 2 2p 5 1s 2 2s 2 2p 6 Ne

5. Write out the electron configuration for the following atoms and ions: He Ne Ar Kr H - Ca +2 O -2 Br - Which noble gas is isoelectronic with each ion?

6. NaCl NaCl + - electron transfer and the formation of ions ionic bond This is the formation of an ionic bond. Cl Cl 2 covalent bond This is the formation of a covalent bond. sharing of a pair of electrons and the formation of molecules

7. What about the distance between the atoms in a bond? NaCl Na + Cl - d = 281 pm Cl 2 Cl-Cl d = 199 pm What property can be used to tell when a bond will ionic or covalent?

8. ionic covalent HClH2OH2OCH 4 MgOCaCl 2 Na 2 S Draw the Lewis dot structures for the following compounds:

9. Some exceptions to the Octet Rule BF 3 PCl 5 SF 6

10. Electronegativity Chlorides of Period 2 compound LiClBeCl 2 BCl 3 CCl 4 NCl 3 OCl 2 Cl 2  EN 2.21.61.10.60 0 Chlorides of Period 3 Compound NaClMgCl 2 AlCl 3 SiCl 4 PCl 3 SCl 6 Cl 2  EN 2.21.91.61.31.00.60 large differencesmall difference The electronegativity difference -  EN = EN higher – EN lower

11. Using electronegativities to determine bond type  EN > 1.7 ionic bond - transfer  EN < 1.7 covalent bond - sharing So we have a range of electronegativity difference of 0 to 1.7 for sharing an electron pair.

12. Is the sharing of electrons in molecules always equal? XY  EN = 0 XY  EN = 0.3 XY  EN = 0.6 XY  EN = 0.9 XY  EN = 1.2 EN Y > EN X Which element is more electronegative? non-polar bond increasing polarity of bond polar bond 0 < EN < 1.7 Direction of electron migration

13. BF 3 – a planar molecule Ball & stick B F Space-filled Electrostatic potential maps top side negative positive Spartan ‘02 2.0 4.0

14. More sharing examples O2O2 N2N2 O ONNOOO O NNNN NN double bond (2 pairs) triple bond (3 pairs) Share until octet is complete. octet complete

15. Bond Energy F 2 single bondBE = 142 kJ/mole O 2 double bondBE = 494 N 2 triple bondBE = 942 X 2 + energy  X + X increasing bond strength Is breaking a bond an endothermic or exothermic process? http://wulfenite.fandm.edu/Data%20/Table_6.html

16. NH 3 NH H H NH H H H+H+ NH 4 + NH 3 + H +  NH 4 + coordinate covalent bond (the pair of electrons from the same atom) normal covalent bond (each atom supplies an electron) Some more sharing examples

17. Type of bond? – I, PC, or NC TiO 2 CH 4 NaI CS 2 CO 2 KCl AlCl 3 CsFHBr

18. Using the EN trends to predict bond type 105 Db 107 Bh Increasing EN NORbFFeSH2SH2S Modified from http://www.cem.msu.edu/~djm/cem384/ptable.htmlhttp://www.cem.msu.edu/~djm/cem384/ptable.html

19. Draw the Lewis dot structures CO 2 H3O+H3O+ CO H 2 CO NH 2 - HCN (C in center)

20. Show the direction of electron migration ( ) in the following. C – H H – F C = O C – Cl Rank the bond polarity (1-most … 3-least) As-H N-HP-H

21. Here is the electrostatic potential map for H 2 CO. Show the electron migration on this planar molecule. C O H H How is this molecule different than BF 3 ? blue – positive red - negative

22. ioniccovalent valence electrons Comparison of Bonding Types sharing of electrons transfer of electrons ions molecules  EN > 1.7  EN < 1.7 high mplow mp molten salts conductive non- conductive

23. Bonding spectrum 100% covalent100% ionic A + B - A B Increasing  EN Increasing polarity Transfer