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Che 131 Notes Ch. 8 - Che 131 Notes Chapter 8 Covalent...

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Che 131 Notes Chapter 8: Covalent Bonding Lecture 15: Covalent Bonding – Single and Multiple Bonds Reading: 8.1-8.5 I. 8.1 Covalent Bonding A. 1916 G. N. Lewis: explanation of bonding 1. valence electrons rearrange to give noble gas electron configurations when atoms join together chemically 2. covalent bond : attractive force that results when one or more pairs of electrons are shared between the bonded atoms a. covalent bonds, which are shared electron pairs, connect the atoms in molecular (covalent compounds) B. sharing electrons provides an attractive force between bonded atoms because 1. when two atoms get close enough together, their electron clouds overlap, and electrons from each atom are attracted by the other atom’s nucleus, causing a net attraction between the two atoms a. most stable at a certain distance, any closer and the repulsive forces between the nuclei start to take over II. 8.2 Single Covalent Bonds and Lewis Structures A. The number of covalent bonds an atom can form is determined by the number of electrons that the atom must share to achieve a noble gas configuration (Lewis) B. Single covalent bond : formed when two atoms share a pair of electrons C. Octet rule : to form bonds, main group elements gain, lose, or share electrons to achieve a stable electron configuration characterized by eight valence electrons 1. for atoms with more than two valence electrons 2. shared electrons are counted with each of the atoms in the bond D. Lewis structure used, bonds shown as shared dots or lines 1. Bonding electrons : shared electron pairs 2. Lone pair electrons : unshared pairs E. The number of electrons that an atom of a main group element must share to achieve an octet equals eight minus it A group number F. Writing Lewis Structures 1. Count the total number of valence electrons in the molecule or ion a. Use the A group number in the periodic table as a guide to indicate the number of valence electrons in each atom b. Ions i. Neg: add electrons equal to the ion charge ii. Pos: subtract the number of electrons equal to the charge 2. Use atomic symbols to draw a skeleton structure by joining the atoms with shared pairs of electrons (a single line) a. Skeleton structure indicates the attachment of terminal atoms 2 a ctrl atom b. The central atom is usually the one written first in the molecular formula i. One that can form the most bonds ii. H, O, and the halogens are often terminal bonds
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3. Place lone pairs of electrons around each atom (except H) to satisfy the octet rule, starting with the terminal atoms 4. When steps 1 – 3 result in a structure that does not use all the valence electrons or fails to give an octet of electrons to each atom that should have an octet: a. Place any leftover electrons on the central atom, even if it will give the central atom more than an octet i. If the central atom is from the third or a higher period, it can accommodate more than an octet of electrons b. If the number of electrons around the central atom is less than eight, change single bonds to the central atom to multiple bonds i.
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