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Covalent Bonding

Covalent Bonding. Happens between nonmetals Share valence electrons between atoms Electron clouds overlap Ex: H 2 O CH 4 C 6 H 12 O 6 NH 3 CO 2. Electronegativity. Difference in EN is smaller than in ionics and is usually < 1.7 Ex: HCl H = 2.2 Cl = 3.2

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Covalent Bonding

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  1. Covalent Bonding • Happens between nonmetals • Share valence electrons between atoms • Electron clouds overlap Ex: H2O CH4 C6H12O6 NH3 CO2

  2. Electronegativity • Difference in EN is smaller than in ionics and is usually < 1.7 • Ex: HCl H = 2.2 Cl = 3.2 Difference = 1.0

  3. Bond Polarity • Polar Bond: when there is a difference in EN values. (unequal sharing) • Ex: H Cl EN=2.2 EN=3.2

  4. NonPolar Bond: no difference in EN values. (equal sharing) Ex: O2, N2, Cl2, H2 (all the diatomics!)

  5. Single, Double, Triple Bonds • Atoms can share single double or triple bonds between them. • Each bond represents a shared pair of electrons. • http://youtu.be/1wpDicW_MQQ

  6. Naming Covalent Compounds • Use prefix system to indicate the number of atoms of each element present. • Mono • Di • Tri • Tetra • Penta • Hexa • Hepta • Octa • Nona • Deca

  7. Molecular Formulas • Covalent compounds are molecules. • Molecular formulas: show actual number of atoms of each element present in compound Ex: H2O 2 hydrogen atoms and 1 oxygen

  8. Structural Formulas • Show how the atoms are bonded together in a covalent molecule. • Use “lines” to show covalent bonds

  9. Empirical Formulas Empirical formulas: • Show simplest whole number ratio of atoms or ions in the compound. • Ionic compounds are “salts” or ionic crystals. • All ionic compounds have empirical formulas • Ex: MgCl2 1 : 2 ion ratio

  10. You can simplify some molecular formulas to make them empirical ratios Ex: C6H12O6 Simplest ratio of atoms CH2O

  11. Molecule vs. Ionic Crystal CH4 = 5 atoms in molecule NaCl = 1:1 ion ratio

  12. Properties of Covalent Compounds

  13. Melting Point • Lower than Ionics • To melt, you are only separating the weak bonds between molecules (not within).

  14. Melting Point • Polar Molecules (dipoles/”mini-magnets”): • Have higher melting points than non-polars because they are harder to separate.

  15. Solubility • Polar Molecules dissolve in Polar Solvents (like H2O, CHCl3, NH3 etc.) • Non-polar Molecules dissolve in Non-Polar Solvents (like hexane, CCl4) “Like Dissolves Like”

  16. Conductivity • Covalent Molecules do not conduct well as they do not form ions. • Except Acids!!!! • Acids are covalently bonded but in water (aqueous) they will ionize and conduct current. • (Acids are not on this test)

  17. Decompose • If the heat gets high enough covalent compounds will break down and decompose. • (Remember the lab, sugar melted first, then it burned and turned into black carbon)

  18. Shapes of Molecules And how do you draw them?

  19. VSEPR • Valence Shell Electron Pair Repulsion • Valence electrons will orient themselves around the “central” atom to be as far apart from each other as possible. • This influences the “shape” of the molecule.

  20. Polarity of a Molecule • Polar Molecules: • Have polar bonds and are not symmetrical • Nonpolar Molecules • Have nonpolar bonds OR • Have polar bonds and are symmetrical

  21. Regents Shapes to Know: • Tetrahedral • Pyramidal • Bent • Linear

  22. Honors Shapes to Know: See Honors Packet • Linear • Trigonal Planar • Bent (with 3 e- regions and with 4) • Trigonal Pyramidal • Tetrahedral • Trigonal Bipyramidal • SeeSaw • T-Shaped • Linear • Octahedral • Square Pyramidal • Square Planar • VSEPR SHAPES FOR HONORS • http://youtu.be/FjjhUI4wFTE • Example of Shapes (honors) • http://youtu.be/i3FCHVlSZc4

  23. Tetrahedral • Has 4 atoms bonded (no free pairs)

  24. Symmetry? Depends on what atoms are attached. Can be polar (asymmetrical) or nonpolar (symmetrical)

  25. Pyramidal • Three atoms bonded (one free pair)

  26. Symmetry? • All pyramids are asymmetrical. • These molecules are always POLAR!

  27. Bent • Two atoms attached (2 free pair) The 2 free pair make it bent and not linear. These are always asymmetrical so are always polar. H2O

  28. Hey, Water is Polar!!!!! Never forget this!!!

  29. Linear • 2 atoms in molecule • Ex: Cl Cl (nonpolar bond, sym., nonpolar molecule) H Br (polar bond, asym., polar molecule) • 3 atoms in molecule

  30. Drawing Polyatomic Ions • Covalently bonded atoms with a group charge • Follow same steps for drawing covalents. • Add or subtract electrons from total valence depending on charge. • Draw brackets around ion and indicate charge. • Ex: (SO4) -2 6 + 4(6) + 2 = 32 electrons

  31. Remember!! • If an ionic compound contains a polyatomic ion it contains both ionic and covalent bonds!!

  32. Coordinate Covalent Bonding • Covalent bond in which one of the bonding atoms donates both of the electrons to the bond. • The other atom donates nothing. Ex: Forming Hydronium Ion

  33. To form this type of bond you must have: • A molecule with a free pair of electrons • Something that needs to gain 2 electrons H+1

  34. Ex: Forming Ammonium Ion

  35. Exceptions to the Octet Rule (Honors) • Less than Octet • Ex: BeH2 • Odd Number of Valence Electrons • Ex: NO • More than Octet • Ex: SF6

  36. Resonance(Honors) • Electrons “resonate” between multiple bonding sites. • Adds strength to all the bonds. • Check if it is possible to draw double or triple bonds at more than one bonding site.

  37. Sigma and Pi Bonds (Honors) • Sigma Bond: • End to end overlap of orbitals • All single bonds are sigma • One of the bonds in a multiple bond is a sigma • Pi Bond: • Side to side overlap of orbitals. • Found in double or triple bonds.

  38. Network Solids • Giant network of covalently bonded atoms. • Large macromolecules • Extremely strong structures • Unusually high M.P. • Do not dissolve Diamonds are a giant network of carbon atoms.

  39. Ex: C (s) (graphite, diamond, buckyball), SiO2 (quartz), GeO2 “Buckyball”

  40. Metallic Bonding • Pure metals or alloys. • Ex: Mg, Fe, Brass, Au, Ni, Cu • “Delocalized” valence electrons move about between all the metal atoms.

  41. Metallic Bonding Properties • Conducts heat and electricity very well Conducts as a solid too! • Does not dissolve in solvents • Malleable and Ductile • Relatively high melting point. • Higher MP than covalents. • Similar MP to most ionics

  42. Metallic Bonding • http://www.drkstreet.com/resources/metallic-bonding-animation.swf

  43. Ionic vs. Covalent Bonding • http://youtu.be/QqjcCvzWwww • http://youtu.be/yjge1WdCFPs • Electronegativity • http://youtu.be/Kj3o0XvhVqQ • Songs • It’s a chemical bond baby” • http://youtu.be/wWUYHHo-zB0 • Dancin Queen (Ionic/Covalent Bonds) • http://youtu.be/BCYrNU-7SfA • Isn’t it Ionic • http://youtu.be/rwRtfrgJL5E

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