Chapter 3 - Ionic Compounds

Chapter Three: Ionic Compounds Introduction to Bonding bonding is the joining of two atoms in a stable arrangement (e.g. H-H bond in H2); there are two different kinds of bonding: • ionic bonds result from the transfer of electrons from one element to another; formed between a metal (left) and nonmetal (right) • covalent bonds result from the sharing of electrons between two atoms; formed when two nonmetals combine or a metalloid bonds to one to form stable bonds, elements will gain, lose, or share electrons to reach the electron configuration of the noble gas closest to them in the table. a molecule is a compound or element containing two or more atoms joined together with covalent bonds. Ions ions are charged species in which the number of protons and electrons in an atom is unequal. ionic compounds consist of oppositely charged ions that have a strong electrostatic attraction for each other. there are two types of ions: cations: positively charged ions • fewer electrons than protons • an atom loses electron(s) to form a cation • by losing one, two, or three electrons, an atom forms a cation with a completely filled outer shell of electrons • smaller than their neutral atoms anions: negatively charged ions • has more electrons than protons • the shell farthest from the nucleus is completely filled with electrons • larger than their neutral atoms the octet rule: a main group element is especially stable when it possesses an octet (8) of electrons in its outer shell Relating Group Number to Ionic Charge for Main Group Elements elements in the same group form ions of similar charge. for metals in groups 1A, 2A, and 3A, the group number is equal to the charge on the cation. for nonmetals in groups 6A and 7A, the anion charge is equal to 8 - the group number (2 and 1 respectively). Common Ions in the Human Body Ionic Compounds an ionic bond is formed when a metal transfers one or more electrons to a nonmetal. the sum of the charges in an ionic compound must be zero overall. the ratio of cation versus anion in an ionic compound depends on the charge of the atoms. how to write a formula for an ionic compound: 1. identify which element is the cation and which is the anion; use the group number of a main group element to determine the charge 2. determine how many of each ion type is needed for an overall charge of zero; when the cation and anion have different charges, use the ion charges to determine the number of ions of each needed 3. to write the formula, place the cation first and then the anion, and omit charges; use subscripts to show the number of each ion needed to have a zero overall charge (when no subscript is written, it is assumed to be 1) Naming Ionic Compounds main group cations (groups 1A-3A) are named for the element from which they are formed. when a metal is able to form two different cations, two naming systems are used: • systematic name: follow the name of the cation by a roman numeral in parentheses to indicate its charge (e.g. Fe2+ - iron (II), Fe • 3+ - iron (III)) common name: use suffix “-ous” for the cation with a smaller charge and the suffix “-ic” for the cation with a higher charge (e.g. Fe2+ - ferrous, Fe3+- ferric) anions are named by replacing the ending of the element name with the suffix “-ide”. name the cation and then the anion. do not specify the charge on the ion nor how many ions of each type are needed to balance the charge. How to Name an Ionic Compound that Contains a Metal with Variable Charge 1. determine the charge on the cation that would make the overall charge zero 2. name the cation and then the anion How to Derive a Formula from the Name of an Ionic Compound 1. identify the cation and anion, then determine their charges; for metals with variable charges, the roman numeral gives the charge on the cation 2. balance the charges 3. write the formula with the cation first, and use subscripts to show how many of each ion is needed to have zero overall charge Physical Properties of Ionic Compounds ionic compounds are crystalline solids with very high melting and boiling points. when ionic compounds dissolve in water, they separate into cations and anions, increasing the conductivity of the solution. Polyatomic Ions a polyatomic ion is a cation or anion that contains more than one atom. Writing Formulas for Ionic Compounds with Polyatomic Ions writing these formulas is the same as writing formulas for ions with single charged atoms. 1. when a cation and anion of equal charges combine, only one of each is needed. when a cation and anion of unequal charges combine, use the ionic charges to determine the relative number of each ion that is needed. 2. name the cation and then the anion; do not specify the charge on the ions nor how many ions of each type are needed to balance the charge.