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Understanding Covalent Bonding and Molecules in Chemistry

Explore the nature of covalent bonds, molecular compounds, and Lewis structures in chemistry. Learn about bond length, energy, octet rule, and resonance structures. Dive into multiple covalent bonds and the concept of a molecule.

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Understanding Covalent Bonding and Molecules in Chemistry

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  1. 6-2 Covalent Bonding

  2. What is a MOLECULE ?

  3. Why would nature favor forming a covalent bond?

  4. Beaker Breaker Based on the their locations on the periodic table are the following covalent bonds or ionic bonds MgCl2 KCl NO3 CO2

  5. Attraction: nucleus of one atom to the electron cloud of the other atom • Repulsion:both nuclei repel…as do both electron clouds • As atoms approach, attraction increases and potential E goes down • Beyond a certain point, repulsion increases and E goes up ∴ bottom of valley on E curve is where there is a balance between attraction and repulsion

  6. MOLECULE: neutral group of atoms held together by covalent bonds • MOLECULAR COMPOUND: a cmpd that is made of molecules • MOLECULAR FORMULA: shows the kinds & #s of atoms making up a molecule i.e. H2O • DIATOMIC MOLECULE: molecule containing only 2 atoms i.e. H2

  7. Characteristics of the Covalent Bond • Bond Length: average distance between 2 bonded atoms (min potential E) In the H2 molecule, the 1s orbitals overlap and result in a increased electron density between the nuclei.

  8. Bond energy: • Energy required to break a chemical bond and form neutral isolated atoms • Measured in kJ/mol (kilojoules/mole) • Positive value • Bond energy and bond length values will vary depending on what atoms an element is bonded to…ave values found on tables P.168)

  9. Octet Rule • Chemical cmpds tend to form so that each atom, by gaining, losing or sharing electrons, has an octet (8) of electrons in its highest (outermost) energy level • Example of exceptions: • H: only has 2 valence e-s to reach stability • B: only has 6 valence e-s “ “ • Some elements have > 8 (occurs when atom bonds with highly electroneg elements & some “d” e-s are involved in bonding

  10. Electron Dot Diagrams • Electron configuration notation in which only the valence electrons of an atom of a particular element are shown, indicated by dots placed around the element’s symbol • F: 1s22s22p5

  11. “other” dot diagram format • Mg: [Ne]3s2 • “paired” electrons are shown as a pair

  12. Lewis Structures • Formulas in which…. • atomic symbols represent nuclei and inner-shell electrons • Dot-pairs or dashed between 2 atoms represent electron pairs in covalent bonds • Dots adjacent to only one atomic symbol represent unshared electrons

  13. Lewis structure Structural Formula: indicates The kind, number, arrangement, and bonds..but NOT the unshared Pairs of the atoms in a molecule

  14. Lewis structure Single bond: covalent bond produced by the sharing on ONE pair of electrons between 2 atoms

  15. Draw the Lewis structure for carbon tetrachloride • CCl4 • See page 171-172 for rules • Total # of valence electrons: • C: 1 x 4 e- = 4 e- • Cl: 4 x 7 e- = 28 e- • Total # = 32 e-

  16. or…..

  17. Draw the Lewis structure for the following molecules: • IBr • CH3Br • F2O • SiCl4 • C2HCl (????)

  18. Beaker Breaker • Draw the Lewis structures showing the bonds for: • HBr • CH4

  19. Multiple Covalent Bonds • DOUBLE BOND • sharing of TWO pairs of electrons between 2 atoms • TRIPLE BOND • sharing of THREE pairs of electrons between 2 atoms • Bond Energies: • triple > double > single • …..triple bonds are stronger and shorter

  20. Draw the Lewis structure for sulfur trioxide, SO3

  21. Draw the Lewis structure for sulfur trioxide, SO3 • S: 6 e- • O: 3 x 6 e- • Total # = 24 e- ?????

  22. Resonance Structures • bonding in molecules or ions that cannot be correctly represented by a single Lewis structure • the experimental properties (observed properties) do NOT support the paper-and-pen structure suggested by the Lewis structure

  23. Draw the resonance structure for sulfur trioxide, SO3 • How many valence electrons? • How are the atoms arranged relative to each other (skeleton structure)? • How must you distribute the valence electrons so all four atoms comply with the octet rule?

  24. Draw the resonance structure for sulfur trioxide, SO3 • S: 6 e- • O: 3 x 6 e- • Total # = 24 e- • (see next slide)

  25. - Lab evidence shows that all three S-O bonds are the same….not 1/3 double and 2/3 single bonding! - The arrow shows that the real structure is an average of all three resonance structures

  26. Covalent-network Bonding Covalent bonding exists throughout a large network of atoms…will be discussed in chapter 12 i.e. carbon atoms in a diamond

  27. Look at sample problems p.171-174 (if extra time at end of class)

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