Valence Electrons? How can energy be lowered? Compare and Contrast: Metals. Compare and Contrast: Ionic Compounds vs Metals

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1 Compare and Contrast: Ionic Compounds vs Metals Ye are the salt of the earth: but if the salt have lost his savour, wherewith shall it be salted? It is thenceforth good for nothing, but to be cast out, and to be trodden under foot of men. ~ Matthew 5:13 PS 110A Hatch Ch. 222 Network Solids High melting T s Brittle solids Don t conduct heat and electricity in solid Often colorless and usually transparent in big chunks (White when powdered) WHY? Network Solids High melting T s Malleable Good conductors of heat and electricity in solid Opaque, with a luster Why??? Many closely spaced energy levels PS 110A Hatch Ch. 223 with mobile electrons Compare and Contrast: Metals vs NonMetals Metals Large atoms Few valence electrons Low ionization energies Easy remove electrons Nonmetals Small atoms Many valence electrons High ionization energies Easily gain electrons Valence Electrons? P1: Fill up these levels for the metal magnesium and determine how many valence electrons this atom will give up easily. 3 2 freedom etc 1 Why do metals and nonmetals react? Principles of reactivity: materials react to lower energy and increase entropy of universe PS 110A Hatch Ch. 224 PS 110A Hatch Ch. 225 How can energy be lowered? Why are comparable energy levels lower in chlorine? Metals lose valence electrons Nonmetals gain valence electrons Process slips downhill energetically PS 110A Hatch Ch The Cl nucleus has 17 protons compared with Na s The electrons are pulled closer to the nucleus in Cl. (Remember the atomic size trend of the Periodic Table.) PS 110A Hatch Ch. 227

2 What are the products? IONS Structure of salts ionic bond bond: electromagnetic attractions of negative and positive ions Positively charged Sodium ions (11 protons, 10 electrons) Negatively charged Chloride ions 17 protons, 18 electrons Electrons belong to individual ions; they are not shared among ions. The charged ions then attract stronglyionic bonding. PS 110A Hatch Ch. 228 Example: 2Na Cl 2 = 2NaCl Demo: crystal models PS 110A Hatch Ch. 229 What about entropy change? Compare and Contrast Electron Location & Mobility 2Na Cl 2 = 2NaCl lots of heat and light Ionic Compounds Metals In going from Na and Cl ions to NaCl salt there is an disorder decrease, but the heat and light given off to surroundings cause an overall increase in entropy. PS 110A Hatch Ch Electrons fixed; localized on individual nucleus (spherical shapes). Atomic types of orbitals. Sea of Electrons mobile; electron density is spread out over many nuclei PS 110A Hatch Ch Compare and Contrast Energy Levels Examples of Ionic Compounds NaCl Al 2 O 3 Na 2 O Ions: same size charge and similar diameter Ions: different size charge and diameter Ions: similar diameter, but different charges IONIC COMPOUND ENERGY LEVELS few levels spaced very far apart many closely spaced levels spread out over many nuclei PS 110A Hatch Ch P2: Why is the size of sodium (yellow) smaller than chlorine (green).? Describe the structure of each compound: Do ions of one type cluster together? What type of ion immediately surrounds a specific ion? How do the answers to these two questions relate to the electric force law? What prediction could you make about the arrangement of ions in any ionic compound? PS 110A Hatch Ch. 2213

3 How does the model explain properties of salts (ionic compounds)? High melting and boiling temperatures? Strong attractions between and ions Attractive forces act over fairly large atomic distances. Brittleness? Strong repulsions when shifting layers. Ions with like charge come together; material shatters to relieve the stress. Conductivity Don t conduct as a solid. Why? Do conduct when molten or dissolved. Why? (Crud in the water is why the hairdryer kills you.) They are called electrolytes. PS 110A Hatch Ch PS 110A Hatch Ch Salts are generally transparent to light Why are they transparent? electron orbitals are localized around individual ions with FEW energy levels, that is, widely spaced most visible photons are not absorbed, just transmitted They may appear white when powdered or cracked. UV absorbed Colored crystals Why are some ionic materials colored? Because they contain transition metals with more energy levels for electrons Example: Ruby and Sapphire Red is not absorbed, but is reflected. This gives ruby the red color. PS 110A Hatch Ch PS 110A Hatch Ch Metal Nonmetal Bond Ionic Bond Na Sodium Atom Cl Chlorine Atom Na Cl Sodium Ion Chloride Ion The octet rule Atoms will most likely form an ion that has the ns 2 np 6 configuration of the closest noble gas atom. Metals take on this configuration by losing electrons Nonmetals take on this configuration by gaining electrons How do we determine how many electrons an element tends to gain or lose? PS 110A Hatch Ch PS 110A Hatch Ch. 2219

4 What Ions Usually Form? Valence Electrons of Main Group Elements Unreactive noble gases don t form ions. P3:Beryllium (Be) will most likely form an ion with what charge? a) 1 b) 2 c) 1 d) 2 Metals lose their valence electrons. Nonmetals gain enough valence electrons to become noble. PS 110A Hatch Ch PS 110A Hatch Ch Families The periodic chart tells us the primary oxidation state Chlorine and Fluorine will form the same types of compounds since their valence electrons are the same number and same orbital type. 3d 3p 3s 2p 2s 9 F 17 Cl 1s 3d 3p 3s 2p 2s 1s PS 110A Hatch Ch Oxidation State : a signed ( or ) number which indicates how many electrons an atom has lost (or could easily lose) or gained (or could easily gain). Negative oxidation states indicate that it is energetically favorable for an atom to gain electrons Examples: Sodium 1 Beryllium 2 Chlorine 1 Sulfur 2 Hey! Its related to the group number on the periodic table! PS 110A Hatch Ch Predicting Formulas for Salts Find the number of electrons lost by metal atom and number gained by the nonmetal. The final number lost by metals must equal final number gained by nonmetal ions. Use the number lost/gained for the other atom s subscript. Examples Mg and O Ca and P Li and N Mg 2 & O 2 MgO Ca 2 & P 3 Ca 3 P 2 Li & N 3 Li 3 N PS 110A Hatch Ch Forming a salt P4: What would the chemical formula for magnesium fluoride (a salt of Mg and F) be? a) MgF b) Mg 2 F c) MgF 2 d) MgF 3 PS 110A Hatch Ch

5 Ionic compounds are neutral (no net charge). What are the ionic charges in the following compounds? The periodic chart tells us the primary oxidation state NaCl KBr MgF 2 Al 2 O 3 Na 1 and Cl 1 K 1 and Br 1 Mg 2 and F 1 Al 3 and O 2 P5: In one of its compounds with oxygen, iron (Fe) has an oxidation state of 3. Which of the following chemical formulas depicts this compound? a. FeO 2 b. Fe 3 O 2 c. Fe 2 O 3 PS 110A Hatch Ch PS 110A Hatch Ch Naming convention for salts The metal comes first with its name unchanged The nonmetal comes second, with the suffix ide appended Examples: Sodium chloride Potassium iodide NaCl KI When Potassium (K) and Chlorine (Cl( Cl) combine the resulting formula is a) KCl b) K 2 Cl c) KCl 2 d) K 2 Cl 3 e) K 3 Cl 2 PS 110A Hatch Ch PS 110A Hatch Ch P6: When Aluminum (Al) and Chlorine (Cl)) combine the resulting formula is a) Al 2 Cl b) AlCl 2 Formula? Aluminum Oxide? Al 2 O 3 c) AlCl 3 d) Al 3 Cl 2 What about K and F, Na and S 2, Fe 3 and O 2. PS 110A Hatch Ch PS 110A Hatch Ch. 2231

6 Nomenclature If there is a possibility of more than one oxidation state indicate the oxidation state. FeO iron (II) oxide Fe 2 O 3 iron (III) oxide Nomenclature If there is a possibility of more than one oxidation state indicate the oxidation state. FeO iron (II) oxide Fe 2 O 3 iron (III) oxide PS 110A Hatch Ch PS 110A Hatch Ch Atoms With Multiple Valences Fe 2 iron II Fe 3 iron III Cu copper I Cu 2 copper II Au gold I Au 3 gold III Sn 2 tin II Sn 4 tin IV Pb 2 lead II Pb 4 lead IV Hg mercury I Hg 2 mercury II Cr 2 chromium II Cr 3 chromium III Mn 2 manganese II Mn 3 manganese III PS 110A Hatch Ch P7: When Calcium (Ca) and Phosphorus (P) combine the resulting formula is a) CaP b) Ca 2 P c) CaP 2 d) Ca 2 P 3 e) Ca 3 P 2 PS 110A Hatch Ch When Magnesium (Mg) and Sulfur (S) combine the resulting formula is Flourine combines with the release of heat and energy a) MgS b) Mg 2 S c) MgS 2 d) Mg 2 S 3 e) Mg 3 S 2 PS 110A Hatch Ch PS 110A Hatch Ch. 2237

7 Ionic vrs.. Metal Bonding Transition Metals? Bonds arise from electrostatic interactions Attractions extend over large distances Charge carriers are mobile Metallic Bonding Ionic bonding They don t follow the Octet Rule. The d electrons invalidate the rule. Manganese forms ions with 2, 3, 4 charge. Would carbon like to gain or lose electrons? It turns out that it likes to share electrons in covalent bonds, which we ll talk about next lecture. PS 110A Hatch Ch PS 110A Hatch Ch. 2239