No Slide TitleThese 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 Electronic Structure All the Group 7 elements have 7 electrons in the outermost shell. 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 F F Patterns: colour The group 7 elements get darker as you go down the group. What colour would you expect astatine to be? F Cl Br I Darker a © Boardworks Ltd 2003 Patterns: physical state Melting Points and boiling points increase as the molecules get bigger. What is the physical state: solid, liquid or gas? gas gas liquid solid Element Size How will Astatine react? F2 Cl2 Br2 I2 F Cl Br I At 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 Displacement theory The attraction of halogens for an extra electron gets greater going up the group: I