Group 16,17,18

chemical weapons (highly radioactive)

highly radioactive

2nd most abundant element - used in NMR (super conducting magnet)

= chalcogens -same periodic trend as in group 13-15 -non-metals = O,S -semi-conductors = Se, Te -others = metallic last group to contain true metal = polonium

ability to form chains

S, Se + Te

max. = +6 (important for S) max. for oxygen = +2 most common = -2,-1,0

O2 and O3

strong oxidising agent -each O has 6 valence e- -central O = sp2 hybridised -1 l.p. in sp2 orbital -1 l.p. in p orbital -each terminal O involved in 1 bond (1 unpaired e- in each) -total of 4e- in p orbitals

how effective an oxidising agent something is

shorter than O-O in H2O2 but longer than O=O in O2

S has more allotropic forms than any other compound + has more compounds with single bonds

decreased tendency to form multiple bonds decreased tendency to catenate (related to bond energies)

bonds get weaker down group (poorer overlap + increased mismatched) reduced stability increased acidity

energy difference between s+p orbitals increases less s-p mixing bonds become more p-like in character H-M-H gets closer to 90°

v. pale blue liquid liquid at rtp more dense and viscous than water oxn state = -1 can be both a strong oxidising agent (acidic conditions) + reducing agent (basic conditions) prone to disproportionation - promoted by storing in glass

only consider fluorides highly reactive [O2F2] -similar structure to H2O2 -prepared by passing electrical discharge through F2 and O2 -solid -decomposes at rtp over days -extremely powerful oxidative fluorinating agent (hard to control) NpF4 + O2F2 -> NpF6 + O2

S2F2 - v. unstable and highly reactive SF4 - acts as both lewis acid and lewis base [why?] 6e- from sulfur and 4e- from fluorine (10e- altogether - hypervalent) expect to act as Lewis acid 10e- to 12e- = expansion of octet F is oxidising enough to allow S to get group oxidation state to +6 should be reactive to H2O but due to high kinetic stability, H2O can’t get past 6 S-F bonds to react high activation barrier to overcome despite favourable reaction thermodynamically SF6 -> SF4/SF2 F-F = weak compared to Cl-Cl no strong driving force for decomposition

involves metal oxides react with acids to produce salt + H2O

involves non-metals reacts with acids to produce salt + H2O

reacts with both acids and bases to produce salt + H2O formed by metalloids and some metals that lie at border of metal/non-metal behaviour

react with neither acid or base

SO2 + SO3 high Zeff elements = smaller behave like elements in the first row

O2 = 2 p-orbitals S8 = 3 p-orbitals (more diffuse ∴ weaker π component - more favourable to have σ-bonds) O=O - strong π component - x2 2p overlap; higher electron density; not v. diffuse S=S - weak π component - x3 2p overlap; v. diffuse SO2 - 2p+3p overlap; 3p contracted due to high Zeff of S; allows π-bonding to occur