Chapter02part2 - Chapter 2: Atoms, Molecules, and Ions...

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CHM 150: McMurry-Fay Chapter 2 Part 2 page 1 of 9 Chapter 2: Atoms, Molecules, and Ions Chapter Exercises: 2.1-2.8; End-of-Chapter Problems: 2.25-2.26, 2.28-2.29, 2.34, 2.38-2.39, 2.42- 2.43, 2.45, 2.48, 2.52, 2.54, 2.60, 2.62-2.63, 2.65, 2.68, 2.70 2.8 MOLECULES, IONS, AND IONIC BONDS When atoms lose or gain electrons, they form charged particles called ions . Metals lose electrons positively charged ions = cations Nonmetals gain electrons negatively charged ions = anions Main-group elements generally form ions—i.e. gain or lose electrons to get the same number of electrons as a noble gas. Charges are shown as superscripts: Group IA elements +1 charge: Li + , Na + , K + , etc. (“+” = “+1”) Group IIA elements +2 charge: Mg +2 , Ca +2 , Sr +2 , Ba +2 ,etc. Group IIIA elements +3 charge: Al +3 Group VA elements –3 charge: N –3 , P –3 Group VIA elements –2 charge: O –2 , S –2 , Se –2 Group VIIA elements –1 charge: F , Cl , Br , I ,etc. monoatomic ions: from a single atom (eg Na + , Cl , O 2– ) polyatomic ions: from 2 or more atoms (eg. OH , MnO 4 , SO 4 2– ) 2.10 NAMING CHEMICAL COMPOUNDS chemical formulas: Symbolically express the number of atoms of each element in a compound Number of atoms is indicated by a subscript following the element’s symbol (If there is no subscript, only one atom of that element is in the compound.) – e.g. H 2 O has 2 H atoms and 1 O atom Some chemical formulas use parentheses more than one of that subunit present in the compound – e.g. Al 2 (SO 4 ) 3 has 2 Al, 3 S, and 12 O Example: How many atoms of each element are in TNT: C 7 H 5 (NO 2 ) 3 ? ___ C atoms, ___ H atoms, ___ N atom, ___ O atoms
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CHM 150: McMurry-Fay Chapter 2 Part 2 page 2 of 9 IONIC COMPOUNDS CATIONS : positively charged ions Metal atoms lose valence electrons to form cations. There are 2 types of cations, so there are 2 different ways to name them. I. Hydrogen and some metals form only one ion , so the ion formed is simply named using: element name + “ion”. II. Other metals can form more than one ion , so the ion is named using the element name + [charge in Roman numerals in parentheses] + “ion”. I. Groups IA, IIA, IIIA elements, silver (Ag), zinc (Zn) and cadmium (Cd) form only one type of ion each: Group IA elements +1 charge always (e.g. Li + =lithium ion) Group IIA elements +2 charge always (e.g. Mg +2 =magnesium ion) – Group IIIA elements +3 charge always (e.g. Al +3 =aluminum ion) silver ion = Ag + ; zinc ion = Zn 2+ ; cadmium ion = Cd 2+ II. The Stock system is used to name most transition metals, Sn, Pb, and other metals that form more than one ion: – e.g. iron (Fe), a transition metal, forms 2 different ions: Fe +2 and Fe +3 , e.g. lead (Pb), in Group IVA, forms 2 different ions: Pb +2 and Pb +4 Na + = ________________________ Co 3+ = ________________________ Ni
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This note was uploaded on 11/12/2011 for the course CHEM chem 2a taught by Professor Cabrera during the Spring '09 term at San Jose City College.

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Chapter02part2 - Chapter 2: Atoms, Molecules, and Ions...

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