As I develop my study guide for general chemistry, I will place general items of interest on this page. These are excerpts from the general chemistry study guide that I am currently writing. Please be warned that converting the formatted text to HTML format results in the loss of symbols (such as delta signs) and super and subscripting. Therefore, this material may be hard to follow in places. Also, I have purged the example problems in this version to conserve on space.
Chapters 11 and 12
Chapters 16 and 18
Main Group Elements - Periodic Trends Increase Going from Left to Right - Nuclear charge - Ionization energy - Electronegativity - Nonmetallic character Decrease Going from Left to Right - Metallic character - Atomic radius Increase Going Down a Column - Metallic character - Atomic radius - Bonding - Metals tend to form ionic compounds with nonmetals - Nonmetals tend to form covalent compounds with other nonmetals Metals - Typically solids - "Shine" - Malleable - Good conductors (heat, electricity) - Low ionization energy - Low electronegativity - Form cations easily - Hydrides are ionic - Oxides are ionic and basic Nonmetals - All physical states represented - Lack luster - Brittle - Poor conductors - High ionization energies - High electronegativity - Form anions - Hydrides are covalent - Oxides are covalent and acidic - Second Row Elements - Only the s and p orbitals are available for bonding - Allows for sigma and pi bonding (review this) - All are relatively small and somewhat highly electronegative - All form a maximum of 4 bonds - Group 3A Elements - Primary oxidation state is +3 (ns2np1) - Going down a column ... metallic character increases - Larger elements also have the possibility for a +1 state Boron - Obtained from Borax, Na2B4O7ù10H2O - Pure boron has high MP and relatively inert - Used in making high strength composites (addition of boron fibers) Boron Compounds - Covalent Bonding - Halides (BCl3, BF3) - B is sp2 hybridized - Behaves as Lewis acids, the B has an empty p orbital - Hydrides - Normally called boranes - Very volatile - Very good reducing agents - H transfers as hydride - B is sp3 hybridized - Geometries are roughly tetrahedral - Simplest compound BH3 is actually a dimer B2H6 - Forms a 3-center, 2-electron bond ... the bridging bonds have been shown to be longer - Group 4 Elements - Metallic character increases going down the column - Most common oxidation state is +4 (ns2np2) - As size increases the possibility for +2 increases .... +4 forms covalent bonds and +2 forms ionic bonds Carbon - One of the most versatile elements - May use sp3, sp2, or sp hybridizations - Allows for sigma and pi bonding - Three forms known: - Diamond (sp3 network) - Graphite (sp2 network) - Fullerenes, spherical network, C60 or larger Carbon Compounds - Will only look at general classes - Oxides - Carbonates - Cyanides - Carbides - Will look at the larger groupings when we take up organic chemistry in chapter 23 - Carbon Oxides (CO and CO2) - Preparation CO 2 C + O2 2 CO CO2 2 CaCO3 CaO + CO2 Fermentation C6H12O6 2CH3CH2OH + 2 CO2 Carbon Monoxide - Used to prepare methanol - Colorless, odorless, very toxic - Hemoglobin binds very tightly with CO (more so than with oxygen) - Low concentrations may cause symptoms Carbon Dioxide - Colorless, odorless, nontoxic - Used to fight fires, carbonation, refrigerant Carbonates - NaCO3ù10H2O, washing soda, basicity of the carbonate ion makes it a good choice for cleaning purposes - NaCO3, soda ash, glass making - NaHCO3, baking soda, reacts with acidic soda to produce CO2, causes dough to rise Cyanides - Referred to as a pseudohalogen because the ion reacts like a halogen - A primary use is in the recovery of metals (Ag and Au) from ores - Lewis base, will react with acids to form HCN which is extremely toxic Carbides - Carbon has a negative oxidation state in these cases - CaC is used in the production of acetylene and is prepared by heating CaO with C - SiC is also referred to as carborundum, second in hardness to diamond and has a diamond-like structure - Excellent industrial abrasive Silicon - Compounds containing this element make up about 990% of the earth's crust - Most common form, SiO2 (quartz, sand) - Pure silicon has a diamond-like structure and in ultra-pure formed used as a semiconductor (less than 1 ppb of impurities) Silicates - Basic building blocks, SiO44-, and Si2O76- - ZrSiO4 (Zircon) is a good example - In nature the more highly bridged species are present (Si2O64-) - Beryl (Be2Al2Si6O18) ... if Cr3+ is present the gem is green (emerald) Germanium, Tin, Lead - Relatively low natural abundances - Extracted from ore: - SnO2, cassiterite - PbS, galena Uses: - Ge: semiconductor, same general structure as diamond - Pb: electrodes, paints, pipes - Sn: bronze (Sn, Cu); pewter (Sn, Pb, Cu); solder (Sn, Pb) - Group 5 Elements - N, P, As, Sb, Bi - Show the expected trends going down a column - Maximum oxidation state +5, min -3 (ns2np3) - N, P include all possible oxidation states - Middle elements ... +5 - Lower elements .... +3 Nitrogen - Colorless and odorless at room temperature - Makes up about 78% of the atmosphere (by volume) - Uses: inert atmosphere, refrigerant, precursor for fertilizers - Decreased reactivity is due to the strong N-N triple bond - reactions usually involve high temperatures and high pressures N2 + 3 H2 2 NH3 Nitrogen Compounds - Ammonia, NH3 - Precursor for fertilizers - Weak base - sp3 hybridized N - BP -33ø, may be used as a solvent - Yields ammonium salts upon reaction with acids HCl + NH3 NH4Cl - Hydrazine, N2H4 - Prepared by reacting ammonia with hypochlorite ion - This is why you don't want to mix bleach and ammonia - Colorless poisonous liquid that can be used as rocket fuel - Nitrogen Oxides - N2O, NO, NO2 - N2O: laughing gas, used to dispense whipped cream - NO: prepared by oxidizing ammonia with oxygen on an industrial scale - Precursor for the prep of nitric acid; also known to protect the heart from low oxygen levels by widening the blood vessels - Nitrogen Acids - Nitrous, HNO2, and nitric, HNO3 - Nitrous acid is used in organic reactions, Sandmeyer - Nitric acid is used in the production of fertilizers such as NH4NO3; it's also classified as a strong acid and oxidizer - Will dissolve most metals (including gold) Phosphorous - This is the most abundant of the group 5 elements in the earth's crust ... mostly found in phosphate rock, Ca3(PO4)2 - Sixth most abundant element in the body (bones, tooth enamel) - Preparation: heat phosphate rock, carbon, silica at 1500øC - P is one of the top industrial chemicals ... fertilizers, food additives, acid prep, detergents - Two forms: white (toxic, tetrahedral, bursts into flames when exposed to air, reactive); red, (more stable, less reactive, not as toxic) Phosphorous Compounds - Phosphine, PH3 - Colorless, poisonous gas, poor proton acceptor (not as basic as ammonia), easily oxidized - Industrial uses: preparation of phosphoric acids, ligands for catalysts - Phosphorous Halides - Prepared by reacting halogens with phosphorous - These compounds are used as reagents to form other halogenated species - Will react readily with water to hydrolyze to phosphoric acid (even moisture in the air will react) - Phosphorous Oxides - React with water to form acids - Look at structures of H3PO3, and H3PO4 and show that one is diprotic and the other is triprotic - Group 6A Elements - O, S, Se, Te, Po - Exhibit the same trend going down a column (O,S nonmetal; Se, Te semiconductor; Po metal) - The outer shell is 2 electrons shy of an octet ... -2 is a common state. As electronegativity decreases higher other states are possible (+4,+6) Sulfur - Sixteenth most abundant element in the earth's crust - Commonly present as sulfide or sulfate (PbS, galena; HgS, cinnabar; CaSO4, gypsum) - Sulfur may be recovered from oil gas by reacting H2S with SO2 to yield S and water - elemental sulfur forms S-S bonds to form 8-membered rings, rhombic sulfur - Heating this causes smaller chains to form (melts) - Cooling the mixture causes a rubbery solid to form, plastic sulfur .... actually a polymer - Sulfur Compounds H2S - Colorless gas that smells like rotten eggs, is actually very toxic - Can be detected by smell at very low concentrations ... overwhelms ability to smell quickly - May be prepared by reacting FeS with acid or by hydrolysis of thioacetamide - This is how you prepared in lab ... [H2S] was kept very low in this manner Sulfur Oxides - SO2, SO3 - Typical acidic properties expected for oxides of nonmetals - Used to prepare H2SO4 which is one of the most important industrial chemicals - Strong, oxidizing acid - Uses: fertilizers, refining, paints, explosives, batteries, rubber - Group 7A - Halogens - Common oxidation state .. -1 (ns2np5) - May exist in positive states when forming halic acids (+1,+3,+5,+7) - Example: chloric acid, perchloric acid ... HClO3, HClO4 (+5,+7) - These are all strong oxidizers - Only the chlorinated analogs have been isolated in pure form - Chlorate salts are also strong oxidizers and should be handled with care - Uses: weed killers, rocket fuels,, bleach, water purification - Examples: NaOCl, NH4OCl4