Ch08 MSJ jlm (1) - Chapter 8 Covalent Bonding Gilbert N...

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1 Covalent Bonding Chapter 8 Chapter 8 Gilbert N. Lewis 1875-1946. Originated idea of shared electrons in chemical bonds. First produced heavy water. Coined the term “photon.”
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2 Most bonding discussed so far has been ionic bonding, i.e., bonding where electrons are transferred from one element to another forming ions . For example, in NaCl: Na gives electron to Cl Which then become: Na + AND: Cl - NaCl is an ionic compound
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3 Transfer is of valence or outer electron or electrons, so that an octet of electrons is achieved . Cl is: Na is: 1s 2 2s 2 2p 6 3s 1 (note: 3s 1 is a valence e - ) The Na + ion is: 1s 2 2s 2 2p 6 Note octet. 1s 2 2s 2 2p 6 3s 2 3p 5 (the 3s 2 3p 5 are valence e’s) The Cl - ion is: 1s 2 2s 2 2p 6 3s 2 3p 6 Na atom + Na ion Cl atom Note octet (We normally “hide” the octet surrounding cations) Cl ion
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4 Each Lewis dot represents a valence electron The number of valence electrons is the same as Group number. Na - Group 1 - one valence electron Na Mg - Group 2 - two valence electrons Mg O - Group 6 - six valence electrons O Ne - Group 8 - eight valence electrons Ne
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5 Octet Rule Atoms tend to gain , lose or share electrons until each is surrounded by 8 valence electrons . This is an octet , or a configuration of s 2 p 6 All inert gases (Group VIII) have s 2 p 6 configuration . Which of following have inert gas configuration? : K K + Mg Mg + Mg 2+ O O 2- N 3- Cl -
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6 Octet Rule Note that the most stable form of atoms or ions from previous slide have an inert gas configuration K + 1s 2 2s 2 2p 6 3s 2 3p 6 = [Ar] Mg 2+ 1s 2 2s 2 2p 6 O 2- 1s 2 2s 2 2p 6 = [Ne] =[Ne] N 3- 1s 2 2s 2 2p 6 =[Ne] Mg 2+ and O 2- and N 3- are isoelectronic
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7 Octet Rule Element electron configurations can be represented as inert gas core plus valence e’s Na = [Ne]3s 1 Al = [Ne]3s 2 3p 1 Cl = [Ne]3s 2 3p 5 Ar = [Ne]3s 2 3p 6 (= [Ar]) K = [Ar]4s 1
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8 Covalent Bonding is the sharing of electrons to achieve octet It usually involves non -metallic elements and hydrogen For example, Cl 2 is: Cl . . . . . . . + Cl x x x x x x x Cl Cl x x x x x x x . . . . . . . Can also use a line to represent a pair of electrons in a bond Cl . x x Cl x x x x . . . . .
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9 Exceptions to octet rule: H, Li, Be, B H can bond with only one other atom. It can never be “sandwiched” X-H X-H-X Methane, CH 4 is: .
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