Bonding Lecture 1 - Bonding, Molecular Shape &...

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Bonding, By Dr. Fawaz Aldabbagh
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Lewis Symbols Represent the number of valence electrons as dots Valence number is the same as the Periodic Table Group Number H Li Be B C N O F Ne He Na; Is 2 , 2s 2 , 2p 6 , 3s 1 = [Ne] 3s 1 Lewis Structure = Na For example, Groups 1 2 3 4 5 6 7 8
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Elements want to achieve the stable electron configuration of the nearest noble gas Atoms tend to gain, lose or share electrons until they are surrounded by 8 electrons Octet Rule Ne
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Nobel Gas Has a Stable Electron Configuration Ar Ne; 1s 2 , 2s 2 , 2p 6 Ar; [Ne] 3s 2 , 3p 6 F Na + Na + + F [ ] _ Electronic configuration of Neon achieved in both cases Example of Ionic Bonding 10 11 9
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Ionic Bonding refers to electrostatic forces between ions, usually a metal cation and a non-metal anion Covalent Bonding results from the sharing of two electrons between two atoms (usually non-metals) resulting in molecules There are two types of bonding; Octet Rule applies H H H H Cl Cl Cl Cl N N N N + number of electrons around each atom = He + number of electrons around each atom = Ar + number of electrons around each atom = Ne Each Covalent Bond contains two electrons Triple bond
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H C H H H methane Carbon has 4 valence electrons C H H H H H C Ne Neon Stable Octet required Covalent Bonding – Atoms Share Electrons
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Hydrogen molecule, H 2 Concentration of negative charge between two nuclei occurs in a covalent bond 7A elements (e.g. F) have one valence electron for covalent bonding, so to achieve octet 6A elements (e.g. O) use two valence electrons for covalent bonding, so to achieve octet 5A elements (e.g. N) use three valence electrons for covalent bonding, so to achieve octet 4A elements (e.g. C) use four valence electrons for covalent bonding, so to achieve octet
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P Cl Cl Cl P Cl Cl Cl Carbon dioxide, CO 2 Double bonds Rules for Drawing Lewis Structures First sum the number of valence electrons from each atom The central atom is usually written first in the formula Complete the octets of atoms bonded to the central atom (remember that H can only have two electrons) Place any left over electrons on the central atom, even if doing so it results in more than an octet If there are not enough electrons to give the central atom an octet , try multiple bonds E.g. 1. PCl 3 Total Number of valence electrons = 5 + (3 x 7) = 26 P Cl Cl Cl O O C O C O C O O + + =
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E.g. 2; CHBr 4 Total Number of valence electrons = 4 + 1 + (3 x 7) = 26 Br C Br H Br Exceptions to the Octet Rule in Covalent Bonding 1. Molecules with an odd number of electrons 2. Other Natural Radicals, which do not obey Lewis Structures (e.g. O 2 ) 1. Molecules in which an atom has less than an octet 3. Molecules in which an atom has more than an octet
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NO Number of valence electrons = 11 N O N O Resonace Arrows O O O O Oxygen is a ground state "diradical" NO 2 Number of valence electrons = 17 O 2 Resonance occurs when more than one valid Lewis structure can be written for a particular molecule (i.e. rearrange electrons)
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Bonding Lecture 1 - Bonding, Molecular Shape &...

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