23.3.1Discuss the similarities and differences in the chemical properties of elements in the same group.Q – What are chemical properties?
3Chemical PropertiesThe chemical properties of an element are largely determined by the number of valence electrons.This explains why members of the same group tend to have similar chemical properties.We’ll start today with a quick review of the groups and their properties…
4Group 0: The Noble Gases Colorless gases Monoatomic Stable due to their full outer energy levels
5Group 1: Alkali Metals Physical Properties: Soft, malleable - easily cut with a knifeLow densitiesLow melting pointsGood conductors of electricityCan you explain these properties based on their atomic structure?
6Group 1: Alkali Metals Chemical Properties: VERY reactive (why?) tarnish rapidly when exposed to airform ionic compounds with non-metals
7Alkali metals react with non-metals to form ionic compounds Alkali metals react readily with oxygen to form oxides.Write the balanced chemical equation for the reaction of lithium with oxygen to form lithium oxide.Alkali metals react readily with halogens to form halides.What would be the general balanced chemical equation for the reaction of an alkali metal with a halogen?2 M + X2 2 MXTry this reaction with sodium and chlorine… potassium and bromine… cesium and iodine …
8Alkali metals in waterAlkali metals react readily with water to form hydrogen and a metal hydroxide. This is why basic solutions used to be called “alkaline”.What would be the general balanced chemical equation for the addition of an alkali metal to water?2 M + 2 H2O 2 MOH + H2Try this reaction with lithium… sodium… potassium…
9Alkali metals in water Li Na K another good one Rb The vigor of the reaction depends on the reactivity of the metal.(Watch the demo and/or the videos below)LiNaK another good oneRbClassic Newsreel: 20,000 Pounds of Sodium Exploding in a Lake(scroll down the page to access this video)Why?
10Group 7: Halogens Physical Properties: melting points increase as you go down a period room temp = gas to liquid to solidColor in pure form (see right)Different colors in water, in hexaneIn water: Cl2 (aq) – pale green; Br2 (aq) – yel-org-br; I2 (aq) - brownIn hexane: Cl2 (aq) – pale green; Br2 (aq) – org; I2 (aq) - violet
11Group 7: Halogens Physical Properties: Diatomic molecules Very electronegative – with F2 being most EN
12Group 7: Halogens Chemical Properties: VERY reactive react with metals (to form ionic compounds - salts)reactivity decreases down the group(a) Sodium metal (immersed in oil to prevent reaction with oxygen and moisture in the air); (b) chlorine gas; (c) the reaction between sodium and chlorine; (d) sodium chloride (common table salt)
13Halides Are the ionic salts formed by halogens and metals Halogen + metal metal halideRemember some of these from earlier in this powerpoint?The reactions that form them are generally fun to watch.The greater the difference in electro negativity, the more vigorous the reaction.Na + ClNa + BrK + BrK + ClH + Cl
14Halides are typically white solids most are soluble in water except… Ag, Pb, & HgThe insoluble silver salts have characteristic colors that can be used to identify the halidesSilver chloride - white (rapidly darkens through purple to black)Silver bromide - off-white / creamSilver iodide - pale yellow
15Halogens in displacement reactions Normally we think of metals duking it out in single replacement (displacement) reactions.Mg + 2 AgNO3 Mg(NO3)2 + 2 AgHalogens can also get in on the fun.2 KBr (aq) + Cl2 (aq) 2 KCl (aq) + Br2 (aq)which can be written as 2 Br- (aq) + Cl2 (aq) 2 Cl- (aq) + Br2 (aq)Br- and Cl2 are basically fighting for electronsWho wins? Why?We can determine the relative reactivity of halogens by letting them try and take electrons from other halide ions. (All in the Family Lab)
16Halogens in displacement reactions Results? : A halogen higher in group 17 will displace a lower halogen from its salts.In a reaction…F2 would displace Cl , Br, I most reactiveCl2 would displace Br and Ibut would NOT displace FBr2 would displace I,but would NOT displace F or ClI2 would NOT displace F nor Cl nor Br least reactive
17Group 7: Halogens More Chemical Properties: react in water to form acidic solutionsresulting acids can act as oxidants – (donate oxygen)bleaching propertytoxic to microbesused as disinfectants & in water treatment
183.3.2Discuss the changes in nature, from ionic to covalent and from basic to acidic, of the oxides across period 3.What is an oxide?What is the nature of bonding of the elements in period 3 with oxygen?What is a base? What is an acid?
19Oxides of Period 3 elements NaMgAlSiPSClArNa2ONa2O2MgOAl2O3SiO2P2O5P2O3P4O10P4O6SO3SO2Cl2O7ClO2Cl2O----Ionic BondingHighly Polar CovalentPolar CovalentBasicAmphotericWeaklyacidicAcidic
20Bases and Acids Simple definitions: Bases produce OH- ions when put in water.Bases can neutralize acids, forming salt and water.Acids produce H+ ions when put in water.Acids can neutralize bases, forming salt and water.
21Reactions of Period 3 Oxides REACTION with WATERNa2O (s) + H2O (l) 2 NaOH (aq)MgO (s) + H2O (l) Mg(OH)2 (aq)Al2O3 (s) H2O (l) No ReactionSiO2 (s) H2O (l) No Reaction(very difficult to break up giant covalent structure)
22REACTION with WATER cont. P4O6 (s) H2O (l) 4 H3PO3 (aq) phosphorous acidP4O10 (s) H2O (l) 4 H3PO4 (aq) phosphoric acidSO2 (g) + H2O (l) H2SO3 (aq)sulfurous acidSO3 (g) + H2O (l) H2SO4 (aq)sulfuric acidCl2O7 (s) + H2O (l) 2 HClO4 (aq)chloric acidCl2O (s) + H2O (l) 2 HOCl (aq) hypochlorous acid
23Reactions of Period 3 Oxides REACTION with acids / basesNa2O (s) HCl (aq) NaCl (aq) + H2O (l)MgO (s) HCl (aq) MgCl2 (aq) + H2O (l)Al2O3 (s) HCl (aq) 2 AlCl3 (aq) H2O (l)Al2O3 (s) + 2 NaOH (aq) + 3 H2O (l) 2 NaAl(OH)4 (aq)SiO2 (s) NaOH (aq) 2 Na2SiO3 (aq) + H2O (l)