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Covalent Molecule Shapes

Covalent Molecule Shapes. Lewis Dot Diagrams. Remember - Lewis Dot Diagrams show the valence electrons. Valence Electrons - electrons in the highest energy shell Valence Electrons are shared/lost/gained between elements to form compounds. Family Lewis Dot Diagrams. Family 1 Family 2

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Covalent Molecule Shapes

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  1. Covalent Molecule Shapes

  2. Lewis Dot Diagrams • Remember - Lewis Dot Diagrams show the valence electrons. • Valence Electrons - electrons in the highest energy shell • Valence Electrons are shared/lost/gained between elements to form compounds

  3. Family Lewis Dot Diagrams • Family 1 • Family 2 • Family 3

  4. Family Lewis Dot Diagrams • Family 4 • Family 5 • Family 6 • Family 7

  5. Connecting Electrons • Electrons shift positions to get away from each other - reduces repulsion • Lone pairs - pairs of electrons not shared with other atoms • Shared pairs - an electron shared with a different atom to form a bond

  6. HCl H is from Family 1 and Cl is from Family 7. Together, the H and Cl share 1 pair of electrons or two electrons total H Note that Family 7 has 3 sets of Lone pairs. Family 1 has no Lone pairs A Lone pair 1 7 A Shared pair

  7. Shared/Lone pair Family patterns • Family 1: 1 Shared pair/0 Lone pairs • Family 2: 2 Shared pairs/0 Lone pairs • Family 3: 3 Shared pairs/0 Lone pairs • Family 4: 4 Shared pairs/0 Lone pairs (can create them though) • Family 5: 3 Shared pairs/1 Lone pair • Family 6: 2 Shared pairs/2 Lone pairs • Family 7: 1 Shared pairs/3 Lone pairs • Lone pairs are very strong repelling forces. Lone pairs will push Shared pairs into positions to create a specific shape

  8. Electron Domains (Directions) • Determines the shape of a molecule • In how many directions are shared and lone pairs facing? • 2 Domains: linear shape • 3 Domains: trigonal planar • 4 Domains: angular/bent, trigonal pyramid or tetrahedral

  9. Shared/Lone Pair combinations and how they create domains and shapes • Linear: 1 or 2 shared pairs • Trigonal Planar: 3 shared pairs • Angular/Bent: 2 shared pairs and 2 lone pairs • Trigonal Pyramid: 3 shared pairs and 1 lone pair • Tetrahedral: 4 shared pairs

  10. Linear • Families 1 + 7 and Families 2 + 7 or 2 Hydrogens or 2 Family 7s • 1 Shared pair between atoms Shared pairs

  11. Linear - Part 2 • Linear bond angle = 180º • Two domains (directions) • On Linear shapes, only the Shared pairs are shown because they determine the shape • Lone pairs if present, won’t affect shape

  12. Linear Shapes - Examples BeBr2 HCl H Cl Br Be Br Shared Pair Shared Pair Xs have been used instead of dots for the Family 7 members. This helps to see where each electron in the shared pair originally come from.

  13. Angular (Also called Bent) • Family 6 (center atom) + Family 7 (or H) • 2 Lone pairs on central atom and 2 Shared pairs between different atoms Lone pair Shared pair

  14. Angular - Part 2 • Bond angle = 105º • 4 domains (directions) • Family 6 is the central atom because it can form the most bonds at one time - 2 (recall its charge) • Lone pairs push the Shared pairs down at an angle

  15. Angular Shapes - Example H2O Lone pairs O H Shared pairs H The Lone pairs push the 2 Shared pairs toward each other, creating an angular shape. The two Lone pairs are trying to get away from each other, but the Shared pairs get in the way, preventing the Lone pairs from getting 180° apart and forming a linear shape.

  16. Trigonal (Triangle) Planar • Family 3 (central atom) and Family 7 or Hydrogen • 3 Shared pairs and 0 lone pairs Shared pairs

  17. Trigonal (Triangle) Planar – Part 2 • Bond Angle = 120º • 3 domains (directions) • Family 3 has only 3 valence electrons – these electrons move far enough away from each other to form a triangle • “Flat” – like drawing a triangle on paper

  18. Trigonal Planar Shape - Example AlBr3 Br Al Br Br Notice how the electrons for Br shifted to make it easy to connect to Al. And the overall shape is a big triangle

  19. Trigonal Pyramidal • Family 5 (central atom) + Family 7 or H • 1 Lone pair on central atom and 3 Shared pairs between different atoms Lone pair Shared pairs

  20. Trigonal Pyramidal – Part 2 • Bond Angle = 107° • 4 domains (directions) • Family 5 has 1 Lone pair which pushes the 3 shared pairs down to form the base of a pyramid • 3 dimensional

  21. Trigonal Pyramidal Shapes - Example The Lone pair repels/pushes the Shared pairs down, closer to each other to form the base Lone Pair Ammonia NH3 N H H N H Shared Pairs H H H

  22. Tetrahedral • Family 4 (central atom) + Family 7 (or H) • 4 Shared pairs and no Lone pairs Shared Pairs

  23. Tetrahedral – Part 2 • Bond Angle = 109.5° • 4 domains • Family 4 can form up to 4 Shared pairs at any one time • 3 dimensional • Like Trigonal Pyramidal – it’s a 3D pyramid but instead of 1 Lone pair at the top of the pyramid, it’s a shared pair

  24. Tetrahedral - Example Methane (carbon tetrahyrdride) CH4 H C H H H Shared pairs C H H H H

  25. Multiple Bonds • The sharing of multiple pairs of electrons between just 2 atoms • Double bond – 2 pairs of electrons (4 e- total) shared • Triple bond – 3 pairs of electrons (6 e- total) shared

  26. Multiple Bonds – Part 2 Triple Bond Shows 3 lines between atoms Double Bond Shows 2 lines between atoms

  27. Multiple Bonds – Part 3 • Found most often when Family 4, 5, or 6 are involved as a central atom • A multiple bond exists if the central atom has more electrons than there are atoms to connect with • Multiple bonds are considered 1 domain (direction)

  28. Multiple Bonds - examples Phosphorus P2 Sulfur S2 P P S S Each phosphorus has 3 electrons to bond with Each sulfur has 2 electrons to bond with

  29. Polarity • Describes how much electron sharing exists between 2 atoms • Nonpolar Covalent = 100% sharing • Polar Covalent = <100% sharing • Ionic = no sharing; only ions (1 positive and 1 negative) present

  30. Polarity – Part 2 • Electronegativity (ELN) describes the attraction an atom has for shared electrons • If ELNs are similar, shared electrons held equally • If ELNs are different, shared electrons shift toward atom with higher ELN e-

  31. Polarity – Part 3 • Look up ELNs for atoms forming the bond and subtract • If difference = 0.0 to 0.4, bond is nonpolar covalent; sharing considered equal • If difference = 0.41 (0.5) to 1.7, bond is polar covalent; sharing occurs, but isn’t equal • If difference = 1.71 or higher, bond is ionic, only ions are present, no sharing occurs

  32. Polarity – Example Chlorine’s ELN = 3.0 Hydrogen’s ELN = 2.1 ---------------------------- Difference = 0.9 PC Hydrochloric Acid HCl H Cl H Cl Shared electrons are pulled toward Cl. This creates a…

  33. DIPOLE

  34. Dipoles • Caused by unequal pulls of atoms for shared electrons • Unbalanced, asymmetrical • Creates temporary or partial +/- ends to the molecules (delta (δ) charges) • Consequence is dipoles try to attract other dipoles or ions for more interactions (ex. dissolving)

  35. Dipoles - examples • Oxygen’s ELN 3.5 greater than Hydrogen’s 2.1. Shared electrons pulled more toward Oxygen. (Shown by arrows) • Hydrogen won’t give up electrons it’s trying to attract, so there are still no ions. • But since the electrons are pulled more toward Oxygen, Oxygen “acts” negative (δ-) and Hydrogen “acts” positive (δ+). • This allows water to attract ions (both kinds) and other dipoles to it. H2O δ- δ+ δ+

  36. Chlorine’s ELN 3.0 greater than Carbon’s 2.5 and Carbon is greater than Hydrogen’s 2.1 • Overall pull is toward Chlorine CH3Cl δ- δ+

  37. A Non-dipole Example • Even though Oxygen’s ELN is greater than Carbon’s, the two oxygens are pulling equally but in opposite directions. • Pulls cancel out – result is a balanced shape – nondipole • Nondipoles can attract only other nondipoles CO2

  38. Covalent Compound Characteristics • Shared electrons • True molecules • Can be solids, liquids or gases but most are gases at room temperature • Generally low melting points and boiling points (that’s why they’re gases) • Do not conduct electricity • Little or weak attraction from one molecule to another • Examples: CO2, H2O, C12H22O11, CH4, NH3

  39. Ionic Bond Characteristics • Positive and Negative ions • Not really molecules; referred to as formula units • Positive/negative attraction very strong • Generally high MP, BP when compared to covalent compounds • Most are solids at room temperature

  40. Ionic Bond Characteristics - 2 • Most dissolve easily in water • Conduct electricity in liquid state and when dissolved • Ionic compounds are brittle. Why? • Examples: NaCl, Na(HCO3), Mg(SO4), Fe2O3, KI

  41. Metallic Bond Characteristics • Alloys: uniform mixture of metals • Metallic bond: free moving electrons (electron sea) surrounding all metal ions • So a metallic “compound” really isn’t a compound but a collection of + metal ions grouped together

  42. Metallic Bond Characteristics - 2 • Electrons given up by metals move freely around all metal ions • Prevents + ions from coming in contact and repelling each other • Results in malleability and ductility • Some metals have low melting points (Ga 30°C) and some have high melting points (W 3422°) • Except for Hg, all metals are solids at room temperature

  43. Brass: Cu + Zn Bronze: Cu + Sn Nichrome: Ni + Cr Solder: Pb + Sn + Ag Galvanized Steel: Fe + Zn + C Stainless Steel: Fe + Cr + C Sterling Silver: Ag + Cu Important Alloys Metals are combined to form alloys because being an alloy improves the basic properties of the individual metals. Alloys melt at higher temperatures and are stronger than the individual metals

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