Ionic Compounds Chapter Four Ionic Compounds Ionic Compound- A compound composed of ions Ions- A particle that carries an overall positive or negative charge These compounds usually contain a metal or a nonmetal 1
Types of Ions- Cations Cation- a positive ion: electrons < protons Types of Ions- Anions Anion- a negative ion; electrons > protons 2
Loss and Gain of Electrons Ionization energy- energy required to remove an electron from an atom in gaseous state Atom + energy --> Cation + electron Electron affinity- energy released to add an electron to an atom in gaseous state Atom + electron --> Anion + energy Cation Formation Small ionization energy- e - easily lost Small electron affinity- e - not easily gained 3
Anion Formation Large ionization energy- e - not easily lost Large electron affinity- e - easily gained Some Common Ions Representative Elements - Group 1: 1+ Group 15*: 3- - Group 2: 2+ Group 16*: 2- Group 17: 1- *Not easily formed Transition metal ions Cr 2+/3+ Mn 2+/3+ Fe 2+/3+ Co 2+/3+ Ni 2+ Cu +/2+ Zn 2+ Ag + Pb 2+/4+ 4
Ions Within the First Four Periods Ionic Compound Properties Ions form when element with small ionization energy (metal) reacts with element with large electron affinity (nonmetal) Resulting ions held together by electrostatic attraction of opposite charges Forms a 3-dimensional crystal structure that - have high melting/boiling points - dissociate into cations and anions when melted - dissolve in water if attraction between water and ions greater than attractions of ions for each other Water soluble and melted ionic compounds conduct electricity 5
Rationale for Ionic Bonding Atoms of reactive elements exchange electrons such as to produce ions: a) that have electronic configurations of the nearest noble gas if at all possible or that have other stable electronic configurations b) that produce salts with strong ion-ion attractions (lattice forces) There is a limit to the number of electrons that can be donated or accepted (+ or - 3) Example Illustrating Rationale for Ionic Bonding 6
Octet and Duet Rules All of the noble gases (except He) have 8 valence electrons - 8 valence electrons is considered to be a particularly favorable electronic arrangement for an atom Octet Rule- In forming compounds, atoms tent to gain, lose or share electrons in such a way as to be associated with 8 valence electrons (limited to main group elements, why?) Duet Rule- For H the nearest noble gas is helium which has 2 electrons Electron Dot Structures of Atoms Electron dot structure help to determine the number of electrons that can be lost or gained to reach a stable octet Valence Electrons- The electrons in the outermost shell of an atom An electron dot structure is obtained by placing the valence electrons as dots around the symbol of an element in a particular pattern 7
To name metal ions Naming Ions - give name of element + ion To name a transition metal ion - give name of element (charge as Roman Numeral) + ion To name a monatomic anion - give root of name together with ide + ion Polyatomic Ions Polyatomic ion- a group of atoms having an overall charge that behaves as a unit - A molecule with a charge See Table 4.4 (overhead) Oxoanions: XO m n- - Except for oxoanions of 2nd period elements, the parent oxonanion of an element has 4 oxygens in its formula - Except for oxoanions of 2nd period elements, the overall charge on anions is the same as that on monatomic anions of that element - Most oxoanions have names that end with ate or ite - The ite anion of a series has one less oxygen atom than the corresponding ate ion - Adding H (as H+)reduces negative charge by -1 8
Formula Unit The formula that identifies the smallest NEUTRAL unit of an ionic compound Naming of Ionic Compounds- General Ionic compounds are composed of cations and anions charges on ions are a consequence of following appropriate bonding strategies some ions are simple, others are complex The overall charge on the compound must be zero. The positive and negative charges must balance each other. Charges on specific ions may not be altered The positive ion always comes first in the formula followed by the negative ion Naming is in the same order as the formula The specific naming depends of the region of the Periodic Table providing the positive metal cation (I.e,, Type 1 or Type 2) 9
Naming of Ionic Compounds To name a compound starting with a type 1 cation (single possible positive charge) Give name of metal (or ammonium) followed by the name of the anion For monatomic anions the ending is always element stem name plus IDE NaCl = sodium chloride K 2 O = potassium oxide For polyatomic ions the name is the specific name of the ion NaNO 3 = sodium nitrate Al 2 (SO 4 ) 3 = aluminum sulfate To name a compound starting with a type 2 cation (more than one possible positive charge) Give the name of the metal followed in parenthesis by the charge given as a Roman Numeral followed by the name of the anion - For monatomic anions the ending is always element stem name plus IDE - For polyatomic ions the name is the specific name of the ion CoCl 2 = cobalt (II) chloride Fe 2 (SO 4 ) 3 = iron (III) sulfate An Example of an Ionic Compound 10
Examples of Ionic Compounds NaCl- (sodium chloride) common table salt Al 2 O 3 - (aluminum oxide) (corundum) Sapphire (with traces of Fe and Ti) Ruby (with traces of Cr) FeS- (iron (II) sulfide) Pyrite (Fool s Gold) Introduction to Acids and Bases Acids and bases are molecular compounds not ionic compounds but have unique chemical properties when added to water Acid- A substance that provides H + ions when added to water Base- A substance that provides OH - ions when added to water See Table 4.6 for common acids and their ions 11
Formulas of Acids and Bases All acids are covalent compounds! Formulas and names of acids are related to those of their corresponding anions. The number of hydrogens in the formula of an acid equals the number of negative charges on its corresponding anion. The names of acids are related to the names of the corresponding anions. Binary Acids - Contain only H and one other element. H n X - examples: HCl, H 2 S Oxoacids - Contain H, O and another element H n XO m - examples: H 2 SO 4, HNO 3 12