THE HALOGENS Halogens and the Periodic Table These

THE HALOGENS

Halogens and the Periodic Table These are the Halogens or Group 7 Elements H F Cl Br I Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Li Be B C N O Na Mg Al Si P S K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te Fr Ra Ac Rf Db Sg Bh Hs Mt ? ? ? He Ne Ar Kr Xe Rn

Electronic Structure All the Group 7 elements have 7 electrons in the outermost shell. F Fluorine Cl Chlorine Br 2, 7 2, 8, 7 Bromine I Iodine At Astatine And so on

Halogen molecules All the Group 7 elements are molecules containing two atoms. (They are diatomic) Each atom is 1 electron short of a noble gas electron structure. By sharing electrons in a covalent bond full outer electron shells are achieved. F F

Patterns: colour The group 7 elements get darker as you go down the group. F Darker Cl Br I Bromine solution. Note the bromine vapour above the liquid What colour would you expect astatine to be?

Patterns: physical state Melting Points and boiling points increase as the molecules get bigger. What is the physical state: solid, liquid or gas? Element Size Melting Boiling Physical Point (o. C) State Fluorine -220 -188 gas Chlorine -101 -35 gas Bromine -7 59 liquid +114 184 solid Iodine

Patterns: reactivity Reactivity increases up the group. Cl Br I At Increasing Reactivity F For example, their reaction with hydrogen F 2 Reacts instantly even at 200 C Cl 2 Reacts slowly in dark. Explodes in light Br 2 Needs heating to +200 C in order to react Does not react completely even at 500 C I 2 How will Astatine react?

Reactivity and electron structures Most halogen reactions involve gaining an electron. Reactivity decreases 1. The atoms get bigger as you go down the group. This reduces the attraction of the (+) nucleus for an additional (-) electron. 2. ‘Shielding’ by the inner electron shells also reduces the attraction from the nucleus. As we go down the group the tendency to gain electrons decreases and so does the reactivity

Displacement reactions A more reactive halogen will displace a less reactive halide from its compounds in solution. Chlorine + sodium bromide sodium chloride + bromine Cl 2(aq) + 2 Na. Br(aq) 2 Na. Cl(aq) + Br 2(aq) very pale green no colour red colour

Displacement theory • The attraction of halogens for an extra electron gets greater going up the group: I <Br<Cl<F. Na+ Cl- F • If we mix a metal halide with a more reactive halogen, the electron will be transferred from the less to the more reactive halogen. Na+ e- Cl F-

Reactions with metals The attraction of halogens for an extra electron means that they readily react with most metals. Chlorine reacts readily with iron on gentle heating despite iron’s low reactivity. Chlorine + iron (III) chloride 3 Cl 2(g) + 2 Fe(s) 2 Fe. Cl 3

Reactions with non-metals Halogen atoms have 7 electrons in the outer shell. They seek to achieve a full shell (8 electrons). With metals they gain electrons forming ionic compounds. With non-metals they react by sharing electrons and forming covalent compounds. For example, hydrogen and chlorine form hydrogen chloride. H Cl Cl H

Uses of Fluorine, often via hydrogen fluoride, is used to manufacture many other products. Fluorine and its compounds Processing uranium nuclear fuel fluorine-containing polymers, e. g. Teflon Toothpaste, to prevent tooth decay Fluoridation of water

Uses of Chlorine antiseptics and disinfectants pesticides and weed killer Chlorine and its compounds Bleach to kill bacteria and to make paper white Drinking water treatment HCl Chlorinated carbon compounds, e. g. solvents and plastics (PVC)

Uses of Bromine and Iodine Leaded petrol (being phased out) Bromine and its compounds medicines photography agriculture Iodine and its compounds Animal feed supplements antiseptic

Uses of Halogens Link up the halogen with the uses. F I Cl Br

Across: 2 Reactivity does this going up group 7 5 Added to animal feeds 7 Number of outer shell electrons in halogens 8 Used in the swimming pool 9 Used in photography Down: 1 Name for Group 7 Elements 3 Most reactive halogen 4 Type of compounds formed with non-metals 6 Type of compounds formed with metals 1 2 3 5 6 7 8 9 4

How many electrons do the halogens have in their outer shell? A. B. C. D. 1 5 7 8

How many atoms exist in a halogen molecule? A. B. C. D. 1 2 5 7

What is the order of increasing reactivity of the halogens? A. B. C. D. F, Cl, I, Br F, Cl, Br, I I, Cl, Br, F I, Br, Cl, F

Which of the pairs of reactants will NOT result in a displacement reaction? A. B. C. D. Iodine + sodium chloride Fluorine + sodium chloride Chlorine + sodium iodide Bromine + sodium iodide