Midterm is Friday, March 24 Chapters 5-8 (except today’s material) Important reminder! Midterm is Friday, March 24 Chapters 5-8 (except today’s material) 4/6/2019

Group 1A elements (ns1, n  2) M M+1 + 1e- 2M(s) + 2H2O(l) 2MOH(aq) + H2(g) metal hydroxides 4M(s) + O2(g) 2M2O(s) metal oxides Increasing reactivity 4/6/2019

Alkali Metals Alkali metals (except Li) react with oxygen to form peroxides (O22- anion): 2Na + O2  Na2O2 K, Rb, and Cs also form superoxides (O2- anion): K + O2  KO2 Alkali metal ions colorless, but produce bright colors when placed in flame. 4/6/2019

Group 2A elements (ns2, n  2) M M+2 + 2e- Be(s) + 2H2O(l) No Reaction Mg(s) + 2H2O(g) Mg(OH)2(aq) + H2(g) M(s) + 2H2O(l) M(OH)2(aq) + H2(g) M = Ca, Sr, or Ba BeO and MgO form at elevated temperatures; CaO, StO, and BaO form at rt. Increasing reactivity 4/6/2019

Mg(s) + 2H2O(l) Mg(OH)2(aq) + H2(g) Alkaline earth metals Be does not react with water, Mg reacts only with steam, but others react readily with water. Reactivity tends to increase as go down group. Mg(s) + 2H2O(l) Mg(OH)2(aq) + H2(g) 4/6/2019

Group 3A elements (ns2np1, n  2) B is a metalloid; boron does not form binary ionic compounds and is unreactive toward O2 and H2O. Al is most abundant metal in Earth’s crust, found as aluminosilicates. rest of Group 3A are metals 4Al(s) + 3O2(g) 2Al2O3(s) Bauxite is chief ore of Al. 2Al(s) + 6HCl(aq) 2AlCl3(s) + 3H2(g) 4/6/2019

Group 3A elements (ns2np1, n  2) Aluminum forms only tripositive ions. Other 3A elements form both +3 and +1 states with +1 becoming more stable going down the group 4/6/2019

Thermite reaction 2Al(s) + Fe2O3 Al2O3(l) + 2Fe(l) ΔH= -847.6 kJ/mol Enough heat released to raise the temperature to ~3000 oC which causes the products to be molten. This reaction is often used to weld iron and steel (alloys of Fe) parts together. 4/6/2019

Booster rockets 10Al(s) + 6NH4ClO4 4Al2O3(l) + 2AlCl3(l) + 12H2O(g) + 3N2(g) Enough heat released to raise the temperature to 3200 oC which causes 2 gases to expand rapidly. The expanding water vapor and nitrogen lift the rocket boosters with a tremendous force. All the fuel is burned in about two minutes. 4/6/2019

Group 3A elements (ns2np1, n  2) Aluminum forms only tripositive ions. Other 3A elements form both +3 and +1 states with +1 becoming more stable going down the group Metallic elements also form many molecular compounds. AlH3 resembles BeH2 (diagonal relationship, gradual shift from metallic to nonmetallic character from left to right across the periodic table. 4/6/2019

Group 4A elements (ns2np2, n  2) C nonmetal, Si & Ge metalloids, Sn & Pb metals Sn(s) + 2H+(aq) Sn2+(aq) + H2 (g) Pb(s) + 2H+(aq) Pb2+(aq) + H2 (g) 4/6/2019

Group 4A elements (ns2np2, n  2) 4A elements form compounds in +2 and +4 oxidation states. For C and Si, +4 oxidation state is more stable. CO2 more stable than CO SiO2 exists; SiO does not (under normal conditions) +4 is only slightly more stable for Sn; +2 is more stable for Pb 4/6/2019

Group 5A elements (ns2np3, n  2) N & P nonmetals, As & Sb are metalloids, Bi is a metal Elemental N exists as N2 NO, N2O, NO2, N2O4, and N2O5 N accepts 3 e- to form nitride, N3- (most metallic nitrides are ionic compounds) 4/6/2019

Group 5A elements (ns2np3, n  2) P exists as P4 molecules, forms P4O6 and P4O10 2 important oxoacids: N2O5(s) + H2O(l) 2HNO3(aq) P4O10(s) + 6H2O(l) 4H3PO4(aq) 4/6/2019

Group 6A elements (ns2np4, n  2) O, S, Se nonmetals; Te, Po metalloids O exists as O2 S and Se are S8 and Se8 O, S, Se, Te form dianions by accepting 2 e- O forms a large number of molecular compounds with nonmetals 4/6/2019

Oxygen Two allotropes: Three anions: O3, ozone Three anions: O2−, oxide O22−, peroxide O21−, superoxide Tends to take electrons from other elements (oxidation) 4/6/2019

Group 6A elements (ns2np4, n  2) Important compounds of S are SO2, SO3, and H2S. Formation of sulfuric acid: SO3(g) + H2O(l) H2SO4(aq) 4/6/2019

Group 7A elements (ns2np5, n  2) All halogens are nonmetals and exist as X2 2F2(g) + 2H2O(l) 4HF(aq) + O2(g) Increasing reactivity 4/6/2019

Halogens Large, negative electron affinities Therefore, tend to oxidize other elements easily React directly with metals to form metal halides Chlorine added to water supplies to serve as disinfectant (HOCl) 4/6/2019

Group 7A elements (ns2np5, n  2) Halogens have high IE and large negative EA X + 1e- X-1 (halides) X2(g) + H2(g) 2HX(g) Form ionic compounds with alkali and alkali earth metals Form molecular compounds among themselves (ICl, BrF3) and with nonmetals (NF3, PCl5, and SF6) Increasing reactivity 4/6/2019

Group 7A elements (ns2np5, n  2) X2(g) + H2(g) 2HX(g) (when X=F, explosive) Hydrogen halides dissolve in H2O to form hydrohalic acids HF is a weak acid (weak electrolyte) HCl, HBr, HI strong acids (strong electrolytes) Increasing reactivity 4/6/2019

Group 8A elements (ns2np6, n  2) Completely filled ns and np subshells. Highest ionization energy of all elements. No tendency to accept extra electrons. 4/6/2019

Noble, but not completely inert Xe forms three compounds: XeF2 XeF4 (at right) XeF6 Kr forms only one stable compound: KrF2 The unstable HArF was synthesized in 2000. 4/6/2019

Properties of oxides across a period basic acidic 4/6/2019

Properties of oxides across a period basic acidic Classified as acidic or basic depending on whether they produce acids or bases when dissolved in water. Na2O(s) + H2O(l) -> 2NaOH(l) Classified as acidic or basic depending on whether they react with acids or bases in certain processes. Al2O3(s) + 6HCl(aq) -> 2AlCl3(aq) + 3H2O(l) Al2O3(s) + 2NaOH(aq) + 3H2O -> 2NaAl(OH)4(aq) 4/6/2019

Properties of oxides across a period basic acidic Classified as acidic or basic depending on whether they produce acids or bases when dissolved in water. Classified as acidic or basic depending on whether they react with acids or bases in certain processes. CO & NO are neutral; they do not react with H2O to produce an acidic or basic solution. As the metallic character of the elements decreases from left to right across the period, their oxides change from basic to amphoteric to acidic. 4/6/2019