1 / 16

Group 17 -The Halogens

Group 17 -The Halogens . Cl 2. -The only group containing solids, liquids and gases at room temperature -All exist as diatomic molecules -All are volatile Nonmetals - with corrosive fumes -None occur in nature as a pure element. -All are electronegative; HCl , HBr and HI are strong

felcia
Download Presentation

Group 17 -The Halogens

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Group 17 -The Halogens Cl2 -The only group containing solids, liquids and gases at room temperature -All exist as diatomic molecules -All are volatile Nonmetals - with corrosive fumes -None occur in nature as a pure element. -All are electronegative; HCl, HBr and HI are strong acids; HF is one of the stronger weak acids Br2 I2

  2. - Form monoatomic anions with -1 charge. - 7 valence electrons: [N.G.] ns2 np5 - Large negative enthalpy of electronic attraction - Are good oxidizing agentsie. They are good at gaining electrons so that other elements are oxidized in their presence Electronic Properties

  3. Oxidation • -Fluorine, chlorine and bromine are oxidizers that are strong enough • to oxidize the oxygen in water! • When fluorine is bubbled through water, hydrogen fluoride and • oxygen gas are produced. • -Hypofluorous acid (HOF) is an intermediate: • Chlorine and bromine are capable of the same however they need • the presence of sunlight: The oxygen produced in these reactions is particularly reactive, so moist chlorine gas is a much stronger oxidizing agent than anhydrous chlorine – as evidenced by the fact that it can bleach dyes like indigo, litmus and malachite green while anhydrous chlorine cannot.

  4. Reactions with Metals

  5. Reactions with P and S • Halogens react with phosphorus (P4) to give PX3 or PX5. • Halogens react with sulfur (S8) to give S2X2 or SX6(depending on the • ratio of reactants). Many other sulfur-halogen compounds can be • made (including, but not limited to, SX2, SX4 and S2X4). *See http://boyles.sdsmt.edu/pwithcl/reaction_of_white_phosphorus_and.htm for a video of the reaction between phosphorus and chlorine at room temperature.

  6. Disproportionation Reactions • Chlorine gas also reacts with hydroxide anions. The products of this • reaction depend on the temperature of reaction: • Cl2 + 2 OH- → ClO- + Cl- + H2O • These are disproportionation reactions because one oxidation state of • chlorine (Cl2) reacts to give two different oxidation states of chlorine (Cl • and an oxoanion). • Other such disproportionation reactions continue: • 2 ClO− → Cl− + ClO2− • ClO− + ClO2− → Cl− + ClO3− • Sodium chlorate crystals can be heated to undergo yet another reaction: • 4 ClO3− → Cl− + 3 ClO4−

  7. Oxoanions of the halogens • Fluorine, chlorine and bromine only occur naturally as monoatomic • ions (fluoride, chloride and bromide). • Iodine occurs naturally as iodide, but also in some oxygen-containing • anions (“oxoanions”). • Chlorine, bromine and iodine are all capable of forming oxoanions in • which an atom of halogen is surrounded by oxygen atoms. • Because oxygen is more electronegative than all three of these • halogens, the electron density is pulled out onto the oxygen atoms, • leaving the halogen with a positive formal charge: (Note that oxidation states are assigned similarly to formal charge, but treating every bond as 100% ionic, so that both electrons in the bond go to the more electronegative atom.)

  8. Oxoanions of the halogens • Fluorine can only form one oxoanion. Why? • Draw Lewis structures for the four oxoanions of bromine, indicating the • molecular geometry of each. Determine the formal charge of bromine • Atom in each case. • Halogens are electronegative thus they do no tolerate large positive • formal charges. • As the formal charge increases with the number of oxygen atoms, they • increase in oxidizing capacity. • Rank the oxoanions above by strength as an oxidizing agent.

  9. Oxidation State The oxidation state of an element is its formal charge assuming only ionic bonding Electrons are not shared they are placed on the more electronegative element Think of it as determining the charge of the ions in an ionic compound Example: Determine the Oxidation states of positive charges atoms in: 1) LiCl 2) BeCl2 3) BCl3 4) CCl4 Example: Consider the following carbon compounds. Determine the Oxidation State of C. 1) CH4 2) CH3OH 3) CH2O 4) CHOOH 5) CO2

  10. Rules for Assigning Oxidation States 1) Pure elements have oxidation states of 0 2) Ionshave oxidation states that add up to the charge of the ion 3) Hydrogenhas an oxidation state of +1 unless bonded to a less electronegative atom. When bound to metals or boron it has an oxidation state of -1. 4) Fluorinehas an oxidation state of -1 5) Oxygenhas an oxidation state of -2 unless bonded to fluorine or another oxygen. 6) Halogensother than fluorine have oxidation states of -1 unless bonded to oxygen or a more electronegative halogen 7) The rest are determined by the process of elimination, where the oxidation states must add up to the total charge of the molecule or ion.

  11. Oxidation State Determine the oxidation state of all the element in the following molecules: a) H2 H = 0 C = 4 O = -2 0 = C + 2(-2) b) CO2 B = 3 0 = B + 3(-1) c) BF3 F= -1 S = 6 H = 1 O = -2 0 = S +(2(+1) + 4(-2)) = S - 6 d) H2SO4 O = -2 e) SO2ClF F = -1 Cl = -1 0 = S +(2(-2) -1 -1) = S - 6 S = 6 f) IO2F2_ F = -1 -1 = I + (2(-2) + 2(-1)) = I - 6 O = -2 I = 5 O = -2 H = 1 g) HPO42- -2 = P + (4(-2) + 1) = P - 7 P = 5

  12. Oxidation States of Poly Atomic Ions CO32- NO3- 5 4 NO2- 3 SO42- ClO3- PO43- 5 6 5 PO33- ClO2- SO32- 4 3 3

  13. Oxoanions of the halogens The name of an oxoanion depends on how many oxygen atoms surround the central atom To name an oxoanion which has had H+ added, add hydrogen before The ‘old’ name. Remember that the added proton changes the charge by +1! e.g. HCO3- is “hydrogen carbonate”

  14. Oxoacids of the Halogens Note that if enough H+ have been added to render the oxoanion neutral, it is no longer an oxoanion. It is an oxoacid! Note that the hydrogens are attached to oxygen in most oxoacids.* *Phosphorous acid is an exception to this rule. Only two of its hydrogens are attached to oxygen.

  15. Oxoacids of the Halogens • Draw the Lewis structures of sulfurous acid and sulfuric acid, and indicate • the molecular geometry of each. Which of these two acids is stronger? • As a general rule, the strength of an oxoacid increases with the number of • oxygen atoms. • The Pauling’s rules quntify this trend for the strength of oxoacids: For the general formula OpE(OH)q. For multiple protons (i.e. q>1), pKa increases by ~5 every time H+ is removed. Exercise) Estimate pKa values for sulfurous acid, sulfuric acid, hydrogen sulfite and hydrogen sulfate.

  16. Isotopic Enrichment of Uranium UF6 235U is 0.72 % abundant with 238U being 99.28% Uranium ore,U3O8 or "yellowcake“ is dissolved in nitric acid, producing uranyl nitrate UO2(NO3)2. 2) Adding NH4OH gives ammonium diuranate, "ADU", (NH4)2U2O7. 3) Reduction with hydrogen gives UO2, 4) UO2 is converted with hydrofluoric acid (HF) to uranium tetrafluoride, UF4. 5)Oxidation with fluorine yields UF6. Zippe-type centrifuge It requires a centrifuge that can spin at 1,500 Hz (90,000 RPM). This corresponds to a speed of greater than 2 Mach. Ex. Washingmachines operate at only about 12 to 25 Hz during the spin cycle. Very strong, light materials requires that are very precisely machined. Heated to 300 oC At bottom to produce convection currents

More Related