Chemical Properties 3.3.1 HL3-3.ppt

3.3.1 Discuss the similarities and differences in the chemical properties of elements in the same group. Q – What are chemical properties?

Chemical Properties The 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…

Group 0: The Noble Gases Colorless gases Monoatomic Stable due to their full outer energy levels

Group 1: Alkali Metals Physical Properties: Soft, malleable - easily cut with a knife Low densities Low melting points Good conductors of electricity Can you explain these properties based on their atomic structure?

Group 1: Alkali Metals Chemical Properties: VERY reactive (why?) tarnish rapidly when exposed to air form ionic compounds with non-metals

Alkali 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 MX Try this reaction with sodium and chlorine… potassium and bromine… cesium and iodine …

Alkali metals in water Alkali 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 + H2 Try this reaction with lithium… sodium… potassium…

Alkali 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) Li Na K another good one Rb Classic Newsreel: 20,000 Pounds of Sodium Exploding in a Lake (scroll down the page to access this video) Why?

Group 7: Halogens Physical Properties: melting points increase as you go down a period - @ room temp = gas to liquid to solid Color in pure form (see right) Different colors in water, in hexane In water: Cl2 (aq) – pale green; Br2 (aq) – yel-org-br; I2 (aq) - brown In hexane: Cl2 (aq) – pale green; Br2 (aq) – org; I2 (aq) - violet

Group 7: Halogens Physical Properties: Diatomic molecules Very electronegative – with F2 being most EN

Group 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)

Halides Are the ionic salts formed by halogens and metals Halogen + metal  metal halide Remember 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 + Cl Na + Br K + Br K + Cl H + Cl

Halides are typically white solids most are soluble in water except… Ag, Pb, & Hg The insoluble silver salts have characteristic colors that can be used to identify the halides Silver chloride - white (rapidly darkens through purple to black) Silver bromide - off-white / cream Silver iodide - pale yellow

Halogens in displacement reactions Normally we think of metals duking it out in single replacement (displacement) reactions. Mg + 2 AgNO3  Mg(NO3)2 + 2 Ag Halogens 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 electrons Who 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)

Halogens 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 reactive Cl2 would displace Br and I but would NOT displace F Br2 would displace I, but would NOT displace F or Cl I2 would NOT displace F nor Cl nor Br least reactive

Group 7: Halogens More Chemical Properties: react in water to form acidic solutions resulting acids can act as oxidants – (donate oxygen) bleaching property toxic to microbes used as disinfectants & in water treatment

3.3.2 Discuss 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?

Oxides of Period 3 elements Na Mg Al Si P S Cl Ar Na2O Na2O2 MgO Al2O3 SiO2 P2O5 P2O3 P4O10 P4O6 SO3 SO2 Cl2O7 ClO2 Cl2O ---- Ionic Bonding Highly Polar Covalent Polar Covalent Basic Amphoteric Weakly acidic Acidic

Bases 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.

Reactions of Period 3 Oxides REACTION with WATER Na2O (s) + H2O (l)  2 NaOH (aq) MgO (s) + H2O (l)  Mg(OH)2 (aq) Al2O3 (s) + H2O (l)  No Reaction SiO2 (s) + H2O (l)  No Reaction (very difficult to break up giant covalent structure)

REACTION with WATER cont. P4O6 (s) + 6 H2O (l)  4 H3PO3 (aq) phosphorous acid P4O10 (s) + 6 H2O (l)  4 H3PO4 (aq) phosphoric acid SO2 (g) + H2O (l)  H2SO3 (aq) sulfurous acid SO3 (g) + H2O (l)  H2SO4 (aq) sulfuric acid Cl2O7 (s) + H2O (l)  2 HClO4 (aq) chloric acid Cl2O (s) + H2O (l)  2 HOCl (aq) hypochlorous acid 

Reactions of Period 3 Oxides REACTION with acids / bases Na2O (s) + 2 HCl (aq)  NaCl (aq) + H2O (l) MgO (s) + 2 HCl (aq)  MgCl2 (aq) + H2O (l) Al2O3 (s) + 6 HCl (aq)  2 AlCl3 (aq) + 3 H2O (l) Al2O3 (s) + 2 NaOH (aq) + 3 H2O (l)  2 NaAl(OH)4 (aq) SiO2 (s) + 2 NaOH (aq)  2 Na2SiO3 (aq) + H2O (l)

REACTION with acids & bases cont. P4O6 (s) (aq) + 8 NaOH (aq)  4 Na2HPO3 (aq) + 2 H2O (l) (or H3PO3 (aq) - phosphorous acid) P4O10 (s) + 12 NaOH (aq)  4 Na3PO4 (aq) + 3 H2O (l) (or H3PO4 (aq) - phosphoric acid) SO2 (g) + 2 NaOH (aq)  Na2SO3 (aq) + H2O (l) (or H3SO3 (aq) - sulfurous acid) SO3 (g) + 2 NaOH (aq)  Na2SO4 (aq) + H2O (l) (or H2SO4 (aq) - sulfuric acid) Cl2O7 (aq) + 2 NaOH (aq)  2 NaClO4 (aq) + H2O (l) (or HClO4 (aq) - chloric acid) Cl2O (s) + 2 NaOH (aq)  2 NaOCl (aq) + H2O (l) (or HOCl (aq) - hypochlorous acid )

Homework – Section 3.3 Read the text… if you haven’t already. Do Exercise 3.3 # 1-10 Due on __________.