Chem 1120 1st Edition Lecture 20 Outline of Last Lecture I. Periodic Trends and Classes of ElementsII. Group 1A (1) HydrogenOutline of Current Lecture I. Noble GasesII. HalogensIII. Oxygen FamilyCurrent Lecture I. Noble gases, including He, Ne, Ar, Kr, Xe, and Rn, are extremely stable and unreactive, mainly because all 8 electron shells are filled and they have the highest ionization energies. Liquid He (a noble gas with boiling point 4.2K) is sometimes used as a coolant. Ne is used in electric signs, and Ar is used in light bulbs and as an insulating gas between panes in thermal win-dows. Noble gases were considered inert until 1962 with the discovery of a com-pound containing Xe. Noble gas compounds include:These are most important when teaching the VSEPR geometriesHe and Ne compounds are unknown, and He is the second most abundant el-ement in the universe II. The halogens, including F, Cl, Br, I, and At, have outer electron configu-rations of ns2np5. They have large electron affinities and ionization energies and they tend to accept one electron to form anionsThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.The halogens are reactive nonmetals. The monoanions are called halides (X-). At standard state, F2 and Cl2 are yellowish gases, Br2 is a red-brown liq-uid, and I2 is a red-purple solid with high vapor pressureF (fluorine) small, reactive, high electronegativity, strong oxidizing agentCl (chlorine) abundant, biologically important element, strong oxidizing agentBr (bromine) liquid in elemental formI (iodine) least reactive and toxic (as X2) of halogens; weaker oxidizing agent,biological trace elementAt (astatine) radioactiveHalogen properties: very reactive, good oxidizers (because of their elec-tronegativities), react with nearly all metals and nonmetals, can oxidize an-ions of halides below them on the periodic chartProperties of fluorine are unique: fluorine reacts explosively with most ele-ments, and oxidizes waterThe F-F bond is the weakest, then comes I-I, then Br-Br, and then Cl-Cl. The F-F bond is the shortest and the repulsion of fluorine’s lone pairs weakens the F-F bondAll halogens have a -1 oxidation state. All but fluorine also have positive oxi-dation states up to +7 when bonded to more electronegative atomsHydrogen halides: HXHX are acidic and acid strength increases down the series, HF<<HCl<HBr<HI III. Group members of the oxygen family exhibit covalent, ionic behaviorsOxygen and Sulfur are nonmetals and both form many covalent compounds. Oxygen forms many ionic compounds and sulfur forms fewer ionic com-poundsSelenium and tellurium are metalloidsPolonium is a radioactive metalAn allotrope is a different crystalline or molecular form of an element, for ex-ample, O2 and O3 are allotropes of oxygenDioxygen, O2, is a strong oxidant, but O3 is strongerO2 is used by animals for respiration and is a plant waste productOzone, O3, is less stable than O2 and is a toxic, astringent pale-blue gasO3 is a bent, diamagnetic molecule used to purify water to remove bacteria, viruses, and organic contaminants Oxides:Oxygen is the second most electronegative element. It always has a nega-tive oxidation state, except when bonded to F. Acidic oxides like SO2 and SO3 form acids when exposed to water and basic oxides like BaO form a hydrox-ide ion when they react with waterOxides of the metals and metalloids are ionic in low oxidation states (+1, +2,+3) and polar covalent in high oxidation states (+4, +5, +6, +7)Basicity decreases from left to right (Na2O, KO2 basic, SO3 acidic)Metallic oxides have high melting points (solids) and oxides of nonmetals are liquids or gases at standard temperatureHydrogen peroxide = polar, reactive molecule that disproportionates to wa-ter and oxygen in presence of heat, light, some metals, and it is an antisepticEnzymes catalase and peroxidase convert O22- and O2- to water and O2 reduc-ing in vivo damageSuperoxides have an oxidation state of -1/2 and react with water to form