THE HALOGENS

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

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

What colour would you expect astatine to be? Patterns: colour The group 7 elements get darker as you go down the group. Bromine solution. Note the bromine vapour above the liquid F Cl Br I Darker a 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 Point (oC) Boiling Point (oC) Physical State Fluorine -220 -188 Chlorine -101 -35 Bromine -7 59 Iodine +114 184 gas gas liquid solid

Patterns: reactivity F2 Cl2 Br2 I2 Reactivity increases up the group. For example, their reaction with hydrogen F2 Reacts instantly even at -200 C Cl2 Reacts slowly in dark.Explodes in light Br2 Needs heating to +200 C in order to react I2 Does not react completely even at 500 C F Cl Br I At Increasing Reactivity How will Astatine react?

Reactivity and electron structures Most halogen reactions involve gaining an electron. The atoms get bigger as you go down the group. This reduces the attraction of the (+) nucleus for an additional (-) electron. ‘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 Reactivity decreases

Displacement reactions A more reactive halogen will displace a less reactive halide from its compounds in solution. Chlorine + sodium bromide  sodium chloride + bromine Cl2(aq) + 2NaBr(aq)  2 NaCl(aq) + Br2(aq) very pale green no colour red colour no colour

Displacement theory Cl Na+ F- Cl- F e- The attraction of halogens for an extra electron gets greater going up the group: I <Br<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.

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

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

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

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

How many electrons do the halogens have in their outer shell? 1 5 7 8

How many atoms exist in a halogen molecule? 1 2 5 7

What is the order of increasing reactivity of the halogens? 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? Iodine + sodium chloride Fluorine + sodium chloride Chlorine + sodium iodide Bromine + sodium iodide

What halogen is used in non-stick cooking pans? F Cl Br I

What halogen is used in animal feed? Cl Br I

Astatine comes below iodine in Group 7 What might its melting point be (in oC)? A. –225 B. +82 C. +150 D. +300

1 2 3 4 5 6 7 8 9 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 4 5 6 7 8 9