Ionic Compounds and Metals Chapter 7 Ch. 7.1 Chemical bond Cation Anion Vocabulary Ch. 7.2 Ionic bond Ionic compound Binary compound Crystal lattice Electrolyte Lattice energy 2 Objectives Define a chemical bond Describe how ions form Identify ionic bonding and the characteristics of ionic compounds Name and write formulas for binary compounds Polyatomic ion containing compounds Compound with metals that have multiple oxidation states Hydrates 3 4 Forming Compounds The Octet Rule: Atoms become stable by having 8 electrons in their outer energy level (2 for smaller atoms) Similar arrangement of valence electrons for element in the same group. (Ex: ns 1 for alkali metals) Electron arrangements determines chemical properties Presents a model of chemical stability When they have gotten 8 electrons they have achieved NOBLE GAS CONFIGURATION Forming Compounds atoms collide with enough energy outer electrons move to achieve a stable octet of valence electrons (noble gas configuration). atoms formed a new compound Total # of e must remain the same. Electrons are particles of matter. 5 6 1
Forming Compounds Transfer of Electrons.... Na + Cl: [Na] + + [:Cl:] 7 8 Lattice Energy Ionic compounds consist of a crystal lattice of positive and negative ions, which is a repeating pattern of ions. = Na+ = Cl 9 10 Lattice Energy The lattice energy is the energy required to separate the ions from their crystalline solid state. Increases with decreasing ionic size. Increases with increasing ionic charge. Lattice energy decreases as anion gets bigger!! Lattice energy is large due to +2 and 2 Charges; decreases as ions get larger. 11 12 2
Lattice Energy Physical Properties of ionic compounds: The melting point increases as lattice energy increases. Solutions are electrolytes, which conduct an electric current. Force applied to crystals causes them to shatter. Ch. 7.3 Vocabulary Formula Unit Monoatomic ion Oxidation Number Polyatomic ion 13 14 Names and Formulas Rules for naming binary compounds 1. Name the cation first. This is usually a metal. Use element name. 2. Then name the anion using the 1 st syllable of the of the element name and then end in ide. Example: Potassium Chloride (KCl) Magnesium Oxide (MgO) Binary Compound Naming Practice Formula NaF Al 2 S 3 CaO Mg 3 N 2 CaH 2 Name 15 16 Predicting Charge on Ions Can you predict the charge on an ion depending on where it is in the periodic table? Yes, of course. Group numbers can help predict many charges. For groups 1 & 2 they lose electrons and become positive Group 13 loses 3 electrons and are generally positive Groups 15 17 gain electrons and become negative in ions. Predicting Charge on Ions The charge on a monoatomic ion is the Oxidation number Again, oxidation number for many elements in the main group (Groups 1 & 2, 1318) can be predicted by looking at the group number. 17 18 3
Rules For Writing Ionic Compound Formulas 1. Write cation symbol first. (Same as we did in naming them.) 2. Write anion symbol second. 3. Add subscripts such that the sum of the charges is zero. 4. Write the simplest ratio of ions. This is the formula unit. Writing Ionic Formula Example: What is the formula for Aluminum Oxide? What is charge on aluminum when it is an ion? What is charge on oxygen when it is an ion (oxide)? How do we get the charges to balance? 19 20 Method of CrossMultiplying Examples of Writing Formulas (Binary Compounds) What would be the subscripts to make the Sum = 0? Drop the signs and make the numbers subscripts Use it backward knowing compound Figure out charges Name of Compound Lithium oxide Lithium ions and oxide ions Li + O Calcium chloride Calcium ions and chloride ions Ca 2+ Cl Magnesium nitride magnesium ions and nitride ions Mg 2+ N 3 Formula of Compound 21 22 Practice Writing Binary Compound Formulas Name of Compound Lithium iodide Beryllium chloride Calcium oxide Sodium oxide Strontium sulfide Calcium phosphide Formula of Compound Compounds of Metals with Multiple Oxidation States (Multivalent Metals) Includes metals in Groups 3 through 12 of the periodic table And the representative metals in Groups 13 & 14 (Commonly Sn & Pb, but also Ga, In, and Tl) They have more than one Oxidation State So they can form more than one type of positive ion. 23 24 4
Compounds of Multivalent Metals For Example: Copper can exist as Cu + and Cu 2+ Iron can exist as Fe 2+ and Fe 3+ Exceptions: Zn and Ag. Zinc only forms a Zn 2+ ion Ag only forms a Ag + ion 25 Compounds of Multivalent Metals How do chemists distinguish the names of compounds formed these metals? We use Roman numerals in parenthesis after the name of the element. Copper Ion Chloride Ion Formula Name Cu + Cl CuCl Copper (I) Chloride Cu 2+ 2Cl CuCl 2 Copper (II) Chloride 26 Compounds of Multivalent Metals Compounds of Multivalent Metals 27 28 Formulas of Multivalent Metals How to write a formula containing one of these metals. First, look at the name. Example: if it is Manganese (III) it means that it s Mn 3+ The roman numeral is the oxidation number of the ion, not how many there are!!!! Then, you can balance charges as before. Example: MnCl 3 Manganese is 3 + and chloride is always 1. 29 Writing Names of Multivalent Metal Compounds If your given a formula, how do you figure out the name? Determine the charge on the metal ion. Look at the negative ion. Figure out what was needed to make the compound neutral Example: FeCl 3 30 5
What is the oxidation number of Zinc when it s an ion? a) 1 + or 2 + b) 2 + always c) 1 + always d) 1 or 2 What is the formula for iron(ii) oxide? a) Fe 2 O b) FeO 2 c) Fe 2 O 2 d) FeO 32 33 What is the correct name of MnF 3? a) Manganese (I) fluoride b) Magnesium (I) fluoride c) Manganese (III) fluoride d) Magnesium (III) fluoride What is the correct formula for nickel(ii) chloride? a) Ni 2 Cl b) NiC 2 c) NiCl 2 d) Ni 2 Cl 2 34 35 What is the name of PbS 2? a) Lead (IV) sulfide b) Lead (I) sulfide c) Lead (II) sulfide d) Lead (III) sulfide Polyatomic Ions Ions can contain more than one element. An ion with two or more different elements is a Polyatomic Ion In polyatomic ions, the atoms are covalently bonded and the atoms share electrons. Individual atoms have no charge, but the group has an overall charge. Example: SO 4 (Sulfate) 36 37 6
Common Polyatomic Ions Name of Ion Formula Charge Ammonium NH + 4 1+ Hydrogen carbonate HCO 3 1 (bicarbonate) Hydrogen sulfate HSO 4 1 Acetate C 2 H 3 O 2 1 Nitrite NO 2 1 Nitrate NO 3 1 Cyanide CN 1 Hydroxide OH 1 38 Common Polyatomic Ions Name of Ion Formula Charge Dihydrogen phosphate H 2 PO 4 1 Permanganate MnO 4 1 Carbonate CO 3 Sulfate SO 4 Sulfite SO 3 Oxalate C 2 O 4 Monohydrogen phosphate HPO 4 Dichromate Cr 2 O 7 Phosphate PO 3 4 3 39 Compounds Containing Polyatomic Ions 1. When there is more than one polyatomic ion, treat it as if it were a single ion by keeping it together as a unit using parenthesis. 2. Write a subscript outside the parenthesis to show how many units there are of polyatomic ion. 3. Remember that the sum of the charges must equal zero. 40 41 Examples of Writing Formulas (w/polyatomic Ions) Name of Compound Calcium nitrate Calcium ions and nitrate ions Ca 2+ NO 3 1 Sodium carbonate Sodium ions and carbonate ions Na + CO 3 Lead(II) Phosphate lead 2+ ions and phosphate ions Pb 2+ PO 4 3 Formula of Compound Naming Polyatomic Compounds from formulas 1. Positive ion (usually a metal) is named first as before. 2. Negative polyatomic ion name as listed in the chart is second. Note: If you see more than one element after the metal the rest is a polyatomic ion. Look for that group in the chart. 42 43 7
Polyatomic Ion Practice Given name or formula: NaHCO 3 Lithium Acetate Ca(CN) 2 Copper(II) Hydroxide K 2 Cr 2 O 7 Determine formula or name What is the formula for zinc arsenate? Note: You have to type this in. Hit the Shift key (lower right) to get capital letters. If you need parenthesis, hit sym 4 for ( and sym 5 for ). Fe(HCO 3 ) 3 Ammonium Chloride 44 45 Ch. 7.4 Vocabulary Compounds of Hydrates (Ch. 10.5) Ch. 10.5 Hydrate (page 351) Ch. 7.4 Electron Sea model Delocalized electron Metallic Bond Alloy Interstitial alloy Substitutional Alloy Hydrate when there is a specific amount of water in the crystal of a compound. The water molecules are part of the crystal structure of the ionic compound. Many compounds become hydrates by absorbing water from the air. The water then becomes part of its structure. Many of them are used as drying agents (desiccants). 46 47 Compounds of Hydrates When writing a formula for a hydrated compound use a dot ( ) followed by the number of water molecules. Example: CaCl 2 2H 2 O CaCl 2 2H 2 O Water Cl Ca +2 Cl This means that this hydrated chloride compound has 2 molecules of water for each formula unit of calcium chloride. Water 48 8
Compounds of Hydrates CaCl 2 2H 2 O This means that this hydrated chloride compound has 2 molecules of water for each formula unit of calcium chloride. You would call the compound Calcium chloride dihydrate. Rule: Follow the regular name of the compound with the word hydrate. The prefix before hydrate tells you how many water molecules there are. 50 Prefixes for Hydrates Molecules of Water Prefix 1 Mono 2 Di 3 Tri 4 Tetra 5 Penta 6 Hexa 7 Hepta 8 Octa 9 Nona 10 Deca 51 Hydrate Compound Practice Compounds of Hydrates Given Name or Formula MgSO 3 6H 2 O Strontium oxalate monohydrate Ni 3 (PO 4 ) 2 7H 2 O Lead(II) acetate trihydrate Determine the Formula or Name Hydrates can also lose water molecules, usually by heating. They may even have a different color than the hydrated compound. When they lose their water molecules, they become anhydrous (without water). 52 53 Ch. 7.4 Metal Bonding Electron Sea Model There are not enough electrons for the metal atoms to be covalently bonded to each other. We use a delocalized model for electrons in a metal Delocalized Electrons in a Metal The metal nuclei are seen to exist in a sea of electrons. No electrons are localized between any two metal atoms. Therefore, the electrons can flow freely through the metal. Without any definite bonds, the metals are easy to deform (and are malleable and ductile). The more delocalized e, the harder and stronger the metal. 54 55 9
Delocalized Model for Electrons in a Metal Melting Point 56 57 Malleability Metals, above, compared to ionic compounds, below. 58 Alloys Alloys are homogeneous mixtures, metal solutions, really. Substitutional alloys: atoms must have similar atomic size, elements must have similar bonding characteristics. Interstitial alloys: one element much smaller than the other in order to fit into the interstitial sites, e.g. a nonmetal. The alloy is much stronger than the pure metal (increased bonding between nonmetal and metal). Example steel (contains up to 3% carbon). 59 Alloys Common Alloys 60 61 10