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HL3-3

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.

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HL3-3

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  1. Chemical Properties 3.3.1 HL3-3.ppt

  2. 3.3.1 • Discuss the similarities and differences in the chemical properties of elements in the same group. • Q – What are chemical properties?

  3. 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…

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

  5. 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?

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

  7. 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…

  8. 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…

  9. Alkali metals in water • The vigor of the reaction depends on the reactivity of the metal. • (Watch the demo and/or the videos below) • Li • Na • Kanother good one • Rb • Classic Newsreel: 20,000 Pounds of Sodium Exploding in a Lake • (scroll down the page to access this video) • Why?

  10. 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

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

  12. 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)

  13. 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

  14. 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

  15. 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)

  16. Halogens in displacement reactions • Results? : A halogen higher in group 17 will displace a lower halogen from its salts. In a reaction… • F2would 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

  17. 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

  18. 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?

  19. Oxides of Period 3 elements

  20. 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.

  21. 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)

  22. 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 

  23. 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)

  24. 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 )

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

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