8 - Covalent Bonding

8 - Covalent Bonding - Chapter 8: Covalent Bonding 8.1...

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Chapter 8: Covalent Bonding 8.1 Covalent Bonding covalent bond is a shared electron pair that connects the atoms in molecular (covalent) compounds when two atoms get close enough, their electron clouds overlap, allowing the nucleus to attract the other atom’s electrons which results in a net attraction between the two atoms if atoms are too close together, they will repulse each other 8.2 Single Covalent Bonds and Lewis Structures shared electron pairs occupy same shell as valence electrons 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 single covalent bond – two atoms share one pair of electrons Lewis structure – shows all valence electrons as dots or lines that represent covalent bonds octet rule – to form bonds, main group elements gain, lose, or share electrons to achieve a stable electron configuration characterized by eight valence electrons Lewis structures show valence electrons as bonding electrons (shared electron pairs) or lone pair electrons (unshared pairs) Guidelines for Writing Lewis Structures o count the total number of valence electrons in the molecule or ion – make sure to add or subtract electrons if there are charges o use atomic symbols to draw skeleton structure by joining the atoms with shared pairs of electrons with a single line; skeleton structure indicates attachment of terminal atoms to central atoms; central atom is usually one written first in molecular formula o place lone pairs of electrons around each atom (except H) to satisfy octet rule, start with terminal atoms o place any leftover electrons on the central atom, even if it will give the central atom more than an octet (only if central atom is from third or higher period) o if number of electrons around central atom is less than eight, change single bonds to central atom to multiple bonds Lewis structures are useful for predicting number of covalent bonds an atom will form, they do not give an accurate representation of where electrons are located in a molecule or the shape of molecules 8.3 Single Covalent Bonds in Hydrocarbons electron density model is a ball-and-stick model surrounded by space-filling model that represents distribution of electron density on surface of molecule alkanes are often referred to as saturated hydrocarbons because each carbon is bonded to a maximum number of hydrogen atoms alkanes with four or more carbons can be straight-chain, branched-chain, or cycloalkanes – saturated hydrocarbons with carbons joined in rings; i.e., cyclopropane, cyclobutane, cyclopentane, and cyclcohexane functional group – distinctive group of atoms in an organic molecule that imparts characteristic chemical properties to the molecule; i.e., -OH is alcohol 8.4 Multiple Covalent Bonds double bond – 2 shared electron pairs; triple bond
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This note was uploaded on 09/28/2009 for the course CHEM 1A taught by Professor Nitsche during the Fall '08 term at Berkeley.

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8 - Covalent Bonding - Chapter 8: Covalent Bonding 8.1...

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