1 / 37

Ch. 9 Chemical Bonds

Ch. 9 Chemical Bonds. Ch. 9 HW 3,15,23,30,31,33,35,39,43 a-f ,44, 47 a-d ,50, 51,52,57. Review:. Valence electrons are the outer shell electrons of an atom. The are the electrons that participate in chemical bonding. # of valence e -. e - configuration. Group. ns 1. 1. 1A. ns 2.

cara-vasquez
Download Presentation

Ch. 9 Chemical Bonds

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. Ch. 9 Chemical Bonds Ch. 9 HW 3,15,23,30,31,33,35,39,43a-f,44, 47a-d,50, 51,52,57

  2. Review: Valence electrons are the outer shell electrons of an atom. The are the electrons that participate in chemical bonding. # of valence e- e- configuration Group ns1 1 1A ns2 2 2A ns2np1 3 3A ns2np2 4 4A ns2np3 5 5A ns2np4 6 6A ns2np5 7 7A ns2np6 8 8A Core electrons: all non-valence electrons

  3. Chemical Bonds Review: 2p6 2s2 2s2 3s0 1s2 1s2 Al+3 3p0 Atoms seek to obtain a configuration like that of a Noble Gas (octet) through bonding. Electrons are attracted to the nucleus of other atoms by electrostatic forces. N-3 2p6 Atoms naturally form chemical bonds by linking with other atoms to minimize energy Most chemical properties are determined by an atom’s valence electrons

  4. Types of Bonds TedEd: How Atom’s Bond www.youtube.com/watch?v=NgD9yHSJ29I • Ionic Bond (metals & non-metals) • e-’s are transferred from atom to atom • Held by electrostatic attraction • Covalent Bond (b/w non-metal atoms) • Valence electrons are shared • Metallic Bond (between metal atoms) • electrons belong to no specific atom • e-’s flow freely through the substance

  5. Electron Dot Notation Cl 2p5 2s2 1s2 Chlorine has 7 valence e- • Dots that represent the valence electrons are placed around the element symbol • Maximum of 8 • Except H and He only has 2 • Must obey Hund’s Rule • Spread out before pairing • Not used for transition metals

  6. Lewis Dot Symbols for the Representative Elements & Noble Gases 6

  7. - - - - + Li+ Li Li Li+ + e- e- + Li+ Li+ + F F F F F F The Ionic Bond Ionic bond: the electrostatic force that holds ions together in an ionic compound. 1s2 1s22s22p6 1s22s1 1s22s22p5 [He] [Ne] LiF + = 7

  8. E = k Q+Q- r Compound Lattice Energy (kJ/mol) MgF2 2957 Q: +2,-1 MgO 3938 Q: +2,-2 LiF 1036 LiCl 853 Electrostatic (Lattice) Energy Lattice energy (U) is the energy required to completely separate one mole of a solid ionic compound into gaseous ions. Q+ is the charge on the cation Q- is the charge on the anion E is the potential energy r is the distance between the ions Higher ~ more stable NaCl 788 Q: +1,-1 Lattice energy increases as charges increase or ion size decreases. r F- < r Cl-

  9. The solubility rules are directly related to Lattice energy because dissolving ionic compounds involves breaking the ions apart

  10. Lattice Energy Problem • Predict which of the following compounds will have the highest lattice energy? • NaCl MgS MgCl2 Na2S +1 +1 -1 -1 +1 +2 -1 -2 +1 +2 -1 -1 +1 +1 -1 -2 With all period 3 atoms, the greatest ion charges hold together strongest. 2. Predict which of the following compounds will have the highest lattice energy? KBr NaCl LiF RbI Charges are all equal, strongest ionic bond comes from smallest ions (Li and F atoms are in lowest period and thus smaller atoms)

  11. + 7e- 7e- 8e- 8e- F F F F F F lonepairs lonepairs lonepairs lonepairs single covalent bond (2 e-) The Covalent Bond A covalent bond is a chemical bond in which two or more electrons are shared by two atoms. Shared electrons are counted for both to fulfill each atom’s octet A pair of shared electrons is represented as a line between atoms Valence electrons not involved in bonding are called Lone Pair electrons Lewis structure of F2

  12. single covalent bonds H H H H or H H O 2e- 2e- O 8e- O O O C O C O double bonds 8e- 8e- 8e- N N N N triple bond 8e- 8e- Lewis structure of water + + Double bond – two atoms share two pairs of electrons or Triple bond – two atoms share three pairs of electrons or Crash Course: Bonding Models and Lewis Structures: www.youtube.com/watch?v=a8LF7JEb0IA 12

  13. : : : : : : : Covalent Bonding Bonds Formed 4 3 2 1 Atoms will normally have a number of bonds equal to the number of valence electrons needed. 4A: 4 x C single bonds 1 x C double and 2 single bonds 1 x C triple and 1 single bond 2 x double bonds 5A: 3 x N single bonds 1 x N double and 1 single bond 1 x N triple bond 6A: 2 x O single bonds; 1 x O double bond 7A: 1 x F single bond

  14. Lengths of Covalent Bonds Bond Lengths a) Dependent on atomic radius b) Single bond > Double Bond > Triple Bond 14

  15. X (g) + e- X-(g) Electronegativity is the ability of an atom to attract the shared electrons in a chemical bond toward itself. Electron Affinity - measurable, Cl is highest Electronegativity - relative, F is highest 15

  16. The Electronegativities of Common Elements Linus Pauling mathematically determined the measure of attraction between an atom's nucleus and its valence electrons by analyzing bond strength of molecules. Scale is relative from 0 to 4.0 16

  17. F H Polar covalent bond or polar bond is a covalent bond with greater electron density around one of the two atoms d- d+ electron rich region electron poor region d+/-indicates a “partial charge” F H Unequally shared electron density

  18. Polar vs Non-Polar molecules Polar Covalent: bonds comprised of atoms of different electronegativity H-F, H-Cl, H-Br, HI Non-polar covalent: Found between bonded atoms of similar or equal electronegativity NCl3 O2 CH4 Crash Course: Polar & Non-Polar Molecules www.youtube.com/watch?v=PVL24HAesnc

  19. Increasing difference in electronegativity Covalent Polar Covalent Ionic partial transfer of e- share e- transfer e- Classification of bonds by difference in electronegativity Difference Bond Type < 0.5 Pure Covalent 0.5 < and < 2 Polar Covalent  2 Ionic 19

  20. Bond Type Problem Classify the following bonds as ionic, polar covalent, or covalent: StrategyWe follow the 2.0 rule of electronegativity difference and look up the values the bond in HCl The bond in KF the CC bond in H3C-CH3 the bond in AlP • The electronegativity difference between H and Cl is 0.9 Therefore, the bond between H and Cl is polar covalent. (b) The difference between K and F is 3.2, above the 2.0 mark; therefore, the bond between K and F is ionic. (c) The two C atoms are identical; therefore 0, the bond between them is purely covalent. (d) Despite being a Metal and Non-metal, the difference is only 0.6 and is a polar covalent

  21. Drawing Lewis Structures NF3 • Place element with largest number of unpaired electrons in the center • Place other elements around the outside • Add Lewis electron dots • Match up the unpaired electrons • Create Single Bonds • If necessary, create double or triple bonds so every atom has 8 valence electrons. • Hydrogen will only have 2

  22. Lewis Structure Practice Br2 CO2 NH3 H2CO Bozeman Science: Lewis Diagrams www.youtube.com/watch?v=xNYiB_2u8J4

  23. Polyatomic ions Net charge indicated in brackets Many must be described by multiple Lewis structures (resonance) We add a dot (electron) for every - and remove for + • NH4+ • CO3-2 • OH- • NO2-

  24. H H C O H C O H Formal charge on an atom Valence e- in free atom - - = # nonbonding electrons ( total number of bonding electrons ) 1 2 Two possible skeletal structures of formaldehyde (CH2O) Which is correct? An atom’s formal charge is the difference between the number of valence electrons in an isolated atom and the number of electrons assigned to that atom in a Lewis structure. The sum of the formal charges of the atoms in a molecule or ion must equal the charge on the molecule or ion. Method 2: Quicker way to find formal charge: 1. Note how many (#) electrons an atom needs to gain an octet 2. If it has the same # bonds as the #, it’s 0 If it has 1 less bond than the #, it’s -1 ; (2 less = -2) If it has 1 more bond than the #, it’s +1 ; (2 more = +2)

  25. For neutral molecules, a Lewis structure in which there are no formal charges is preferable to one in which formal charges are present. • Lewis structures with large formal charges are less plausible than those with small formal charges. • Among Lewis structures having similar distributions of formal charges, the most plausible structure is the one in which negative formal charges are placed on the more electronegative atoms. (b) is more likely structure Because no formal charge (b) is most likely structure for N2O

  26. H C O H 1 2 Potential CH2O structure #1 -1 +1 ( ) valence electrons nonbonding electrons - - bonding electrons Formal charge = Method 2 C needs 4 e- from 4 bonds, has one less than needed so: -1 Formal charge on C = 4 - 2- ½ x 6 = -1 O needs 2 e- from 2 bonds, has one more than needed so: +1 Formal charge on O = 6 - 2- ½ x 6 = +1

  27. H C O H 1 2 Potential CH2O structure #2 0 0 ( ) valence electrons nonbonding electrons - - bonding electrons Formal charge = Method 2 C needs 4 e- and has 4 bonds: 0 Formal charge on C = 4 - 0- ½ x 8 = 0 Formal charge on O = 6 - 4- ½ x 4 = 0 O needs 2 e- and has 2 bonds: 0 Based on the two possible structures, this one is favored because it has smaller formal charges

  28. Problem: Lewis Structure of Polyatomic ions Write formal charges for the carbonate ion CO3-2. C: Formal charge = 4 – 0 – 4 = 0 Oxygen in C=O: Formal charge = 6 – 4 – 2 = 0 Oxygens in C-O: Formal charge = 6 – 6 – 1 = -1

  29. - - + + O O O O O O A resonance structure is one of two or more Lewis structures for a single molecule that cannot be represented accurately by only one Lewis structure. Ozone *Does not switch back and forth, but is a hybrid between the two structures. Carbonate has 3 resonance structures: C-O bonds are 143 pm C=O bonds are 121 pm However, all bonds in CO3-2 are 131 pm The -2 charge is evenly distributed across the 3 O’s *Play super awesome video (swf file)

  30. Be – 2e- 2H – 2x1e- H Be H 4e- B – 3e- 3 single bonds (3x2) = 6 3F – 3x7e- F B F 24e- Total = 24 9 lone pairs (9x2) = 18 F Exceptions to the Octet Rule The Incomplete Octet BeH2 (Not ionic, but covalent) BF3 30

  31. N – 5e- N O O – 6e- 11e- F F F S F F F Exceptions to the Octet Rule Odd-Electron Molecules Unpaired electron: Radical molecule, very reactive NO The Expanded Octet (central atom with quantum number n > 2) SF6 6 single bonds (6x2) = 12 bonding electrons

  32. Draw the Lewis structure with formal charges of: Phosphate PO4-3 Sulfate SO4-2 Problem: Lewis Structure with Formal Charges

  33. Properties of Ionic Compounds • Generally water soluble (polar dissolves polar) • Dense, brittle, and hard solids • High melting points • Poor conductors in solid form, but good conductors when dissolved in water or molten

  34. Properties of Molecules • Low melting points (dependent on size) • Poor conductors of heat and electricity • Fairly easy to separate in mixtures • Exceptions to properties • Network Covalent Substances • 3D crystal (similar to ionic bond) • Diamond

  35. Metallic compounds • Not limited to octet rule (d orbitals) • Transition metals relatively stable when neutral • Electron sea theory – low ionization energies, e- can easily move from atom to atom • Explains the hardness of metals – difficult to separate • Held together by delocalized electrons • Act like “glue”

  36. Metallic Properties Metallic Properties– typically same as pure metals • Conductive – because electrons can easily come travel from one metal atom to the next metal atom. • Luster (shine) • Malleable

More Related