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Lecture 4

Lecture 4. Lewis Structures and Chemical Bonds Chapter 7 Suggested HW 7.1, 7.3, 7.7, 7.15, 7.17, 7.23, 7.31, 7.37, 7.39, 7.59, 7.61, 7.63, 7.67, 7.69, 7.73, 7.75, 7.77, 7.81, 7.97, 7.99, 7.101, 7.105, 7.107, 7.109, 7.111, 7.115, 7.119, 7.121, 7.125, 7.127, 7.129, 7.139, 7.143, 7.145, 7.147.

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Lecture 4

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  1. Lecture 4 Lewis Structures and Chemical Bonds Chapter 7 Suggested HW 7.1, 7.3, 7.7, 7.15, 7.17, 7.23, 7.31, 7.37, 7.39, 7.59, 7.61, 7.63, 7.67, 7.69, 7.73, 7.75, 7.77, 7.81, 7.97, 7.99, 7.101, 7.105, 7.107, 7.109, 7.111, 7.115, 7.119, 7.121, 7.125, 7.127, 7.129, 7.139, 7.143, 7.145, 7.147

  2. Review • Electrons dictate the chemistry of an atom • Electrons fill orbitals in order or increasing energy 1s  2s  2p  3s  3p  4s  3d  4p  5s  4d  5p … • We can represent the electron configuration of an element by showing the orbital designation or orbital configuration Shell Number of electron in subshell 1s1 subshell 2s22p6 3s23p4 1s2 S  [Ne]3s23p4

  3. Octet Rule and Ions The Octet Rule – Atoms prefer to have 8 electrons in their outer shell (or dubletfor H and He). Valence electrons = outer shell • An ion is an atom that has gained or lost electrons • This results in a net charge on the atom • If an ion has a net (+) charge  cation • If an ion has a net (-)charge  anion Ions tend to form such that they satisfy the Octet Rule

  4. Forming Ions Noble gas configuration ALWAYS satisfy the octet rule Na  (Z = 11)  [Ne] 3s1 Mg  (Z = 12)  [Ne] 3s2 S  (Z = 17)  [Ne] 3s23p4 Cl (Z = 17)  [Ne] 3s23p5

  5. Lewis Representation • American chemist G.N. Lewis had a profound impact on our understanding of chemical bonding. One of his many contributions was a simple way to represent chemical bonds. We call these Lewis Symbols. • Valence Electrons are represented by dots. • A single dot represents an electron • A pair of dots represents two paired electrons sharing an orbital H He N O O2- K Mg2+ I- 1s1 1s2 2s22p3 2s22p4 2s22p6 3s1 [Ne] 5s25p6

  6. Compounds Compound Bond Type Inorganic Compound Organic Compound Covalent Composed of Charged components Ionic Bonds Contains Carbon Cations Anions

  7. Electronegativity Some atoms attract electrons more than others X-Y Electronegativity difference  2 Ionic Bond < 2 Covalent

  8. Electronegativity Predict the type of bond that will form between: Ca and F B and H C and F

  9. Ionic Bonds Ionic bonds do not share electrons – bond forms through charge attraction NaCl Ion Na+Cl- Electron Configuration [Ne] [Ne]2s22p6 Lewis Symbol CaCl2 Ion Ca2+Cl- Electron Configuration [Ar] [Ne]2s22p6 Lewis Symbol

  10. Covalent Bonds Covalent bonds  electrons shared between two atoms. This involves an overlap of atomic orbitals Let’s consider H2 - two hydrogen atoms share electrons. Electrons pair and are shared between both atoms Octet Rule NOT satisfied! Commonly represented as: H H Solid line represents covalent bond

  11. Covalent Bonding Energy Energy 1s1 1s1 s bond Hydrogen Hydrogen

  12. Covalent Bonding – Fluorine (F2) Energy Energy Atomic Orbitals are NOT optimized for bonding 2p5 2p5 2s2 2s2 sp3 sp3 Fluorine Fluorine

  13. Covalent Bonding Energy Energy sp3 sp3 s bond Fluorine Fluorine

  14. Covalent Bonding

  15. Covalent Bonding – CH4 2p2 2s2 sp3 1s1 Carbon Hydrogen (x4)

  16. Covalent Bonding – CH4 sp3 1s1 Carbon Hydrogen (x4)

  17. Covalent Bonding – CH4 sp3 1s1 Carbon Hydrogen (x4)

  18. Covalent Bonding – CH4

  19. Covalent Bonding – NH3

  20. Covalent Bonding – NH3

  21. Covalent Bonding – NH3

  22. Covalent Bonding – NH3

  23. VSEPR Valence Shell Electron Pair Repulsion • Each region of electrons (bond or lone pair) counts as a balloon • Balloons want to spread out as much as possible

  24. Molecular Shapes

  25. Molecule Polarity Will each of these molecules be polar? CH4 CH3F CH2F2 CHF3 CF4

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