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CHEM 1161

Compounds and Their Bonds Tuesday, September 18, 2012 10:25 AM 4.1 Octet Rule •Atoms that are not noble gases form octets o To become more stable o By losing or gaining valence electrons o By sharing valence electrons to form bonds: •Ionic bonds occur when atoms of one element lose valence electrons and the atoms of another element gain valence electrons. An octet • is eight valence electrons • is associated with the stability of the noble gases (except He) •The octet rule states that elements gain or lose electrons and become ions to attain noble gas arrangement. Metals Form Positive Ions • by losing one or more of their valence electrons • with the electron configuration of the nearest noble gas • with fewer electrons than protons Group 1A metals ion 1+ Group 2A metals ion 2+ Group 3A metals ion 3+ •Cation- when an atom loses an electron o Metals typically form cations Nonmetals Form Negative Ions • by gaining one or more valence electrons • with the electron configuration of the nearest noble gas • with fewer protons than electrons Group 5A nonmetals ion 3− Group 6A nonmetals ion 2− Group 7A nonmetals ion 1− •Anions- when an atom gains electrons (nonmetals) 4.2 Properties of Ionic Compounds Ionic Compounds •Consist of positive and negative ions •Have attractions called ionic bonds between positively and negatively charged ions •Have high melting points •Are solid at room temperature An ionic formula • consists of positively and negatively charged ions • is neutral • has charge balance • total positive charge = total negative charge • The symbol of the metal is written first, followed by the symbol of the nonmetal. • metal symbol, nonmetal symbol EX Charge Balance for Na S 2 In Na2S • 2 Na atoms lose their valence electrons to become Na+ ions • an S atom gains 2 electrons to become an S2− ion • subscripts indicate number of each ions to give charge balance total positive charge = total negative charge Na+ Na+ + S2− = Na2S 2(1+) = 2− Write the symbol of the metal first followed by a subscript of 2 and then the symbol of the nonmetal. Ex: Mg2+ and N3− 3(Mg 2+) 2(N3-) = Mg 3+6N2-6 So Mg N3b2cause charges cancel each other out 4.3 Naming and Writing Ionic Formulas Metals that form a single ion include the following: Metal(s) Ion Charge Group 1A 1+ Group 2A 2+ Al 3+ Zn and Cd 2+ Ag 1+ Metals That Form More Than One Cation • Transition metals except for Zn2+, Cd2+, and Ag+ form two or more positive ions (cations). • We use a Roman numeral to identify ionic charge. • Some examples are: Cu2+ copper(II) Pb2+ lead(II) Cu+ copper(I) Pb4+ lead(IV) Fe2+ iron(II) Au+ gold(I) Fe3+ iron(III) Au3+ gold(III) KNOW THIS !! Memorize atoms that form more than one cation EX: name CuCl 2 Copper (II) chloride EX: name Fe O 2 3 Charges to balance: Fe O 3+2 -3 Iron (III) oxide 4.4
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