When Elements Combine Most elements do not occur in nature in pure form – instead they occur in compounds – combinations of two or more elements in fixed proportions We say that the individual atoms of the different elements are held together in these compounds by “chemical bonds” Fundamentally, the nature of chemical bonding is driven by the octet rule – the tendency of atoms to give, take, or share electrons so the outermost energy level (s and p orbitals) is filled.

Types of Chemical Bonding There are three types of chemical bonds ionic bonds connect metals to nonmetals covalent bonds connect nonmetals to nonmetals metallic bonds connect metals to metals What kind of bond connects nitrogen (N) and oxygen (O)? copper (Cu) and tin (Sn)? iron (Fe) and chlorine (Cl)? carbon (C) and fluorine (F)? sodium (Na) and iodine (I)? aluminum (Al) and sulfur (S)?

Ionic Bonding Ionic bonds come from the electrical attraction between positively charged metal ions (cations) and negatively charged nonmetal ions (anions) The Periodic Table shows us that metals generally have three or fewer valence electrons – and the octet rule then tells us that these elements tend to lose electrons and become cations. The Periodic Table also shows us that nonmetals generally have four or more valence electrons – and the octet rule then tells us that these elements tend to gain electrons and become anions.

Naming Ionic Compounds Thus, when a metal combines with a nonmetal, the metal gives up electrons, the nonmetal takes electrons, and the resulting cation and anion are attracted to each other Compounds held together by ionic bonds are called “ionic compounds” Ionic compounds are given names as follows: the name of the cation then the name of the anion cation names = element names anion names = element “root” + “ide”

Naming Ionic Compounds There are two special conditions to keep in mind: Transition metals can have multiple valence states To show which valence state is present, a roman numeral is placed after the element name iron (II) has a +2 charge; iron (III) has a +3 charge Polyatomic ions are groups of covalently bonded nonmetals that behave as a single ion polyatomic ions have their own names (which are listed in the reference table) with the exception of ammonium (NH4+), the polyatomic ions are negatively charged

Naming Ionic Compounds Let’s try some!! Fe (+3) and O Ca and F Pb and S K and OH Zn and CO3 Cu (+1) and C2H3O2 NH4 and Cl iron (III) oxide calcium fluoride lead sulfide potassium hydroxide zinc carbonate copper (I) acetate ammonium chloride

Formulas for Ionic Compounds We use the element symbols of the cation and anion to write “formulas” for ionic compounds Ionic compounds must be electrically neutral Thus the “fixed proportion” of elements in an ionic compound is the number of cations and anions required to balance the total positive and negative charges We write the number of cations/anions required as a subscript to the right of the element symbol Barium chloride = Ba+2 and Cl-1 = BaCl2 Potassium oxide = K+1 and O-2 = K2O

Formulas for Ionic Compounds Let’s try some!! iron (III) oxide calcium chloride hydrogen sulfate aluminum fluoride copper (I) sulfide barium phosphate ammonium hydroxide Fe2O3 CaCl2 H2SO4 AlF3 Cu2S Ba3(PO4)2 NH4OH