1 p-BLOCK ELEMENTS (Part II) Content • Group IV elements – variation in m.p. / b.p. – dissimilarity in properties • oxides • chlorides • Silicon & silicates [essay: 96-1-6] Group IV Elements • The entire family consists of – the elements • Carbon, C • Silicon, Si • Germanium, Ge • Tin, Sn • Lead, Pb – their compounds (oxidation state = +4/+2) • oxide • chloride • Outermost electronic configuration: ns 2 np 2 Group IV Elements • Group IV exhibit the most contrasting properties among the same group, best illustrated by the – increasing metallic character down the group • C (non-metal graphite as conductor; diamond as insulator) • Si, Ge (metalloid semi-conducting) • Sn, Pb (metals conductor) – variation in m.p. / b.p. b.p. m.p.
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p-BLOCK ELEMENTS
(Part II)
Content
• Group IV elements– variation in m.p. / b.p.– dissimilarity in properties
tetrahedral arrangement– cubic unit cell similar to ZnS
Carbon Allotropes
• allotrope: same element with different structures / forms / properties
• 06-1-2a, 98-2-2a, 00-1-1a, 03-AS-7
diamond graphite
Carbon Allotropes
• both have high m.p. / b.p.– giant covalent network with millions of strong
C-C bonds between C atoms– graphite (3700°C) has higher m.p. than
diamond (3550°C)• C atoms in graphite & diamond are sp2- & sp3-
hybridized respectively– C-C bond in graphite has multiple bond character owing
to the sideway overlap of unhybridized p-orbitals– more s-character � e- being held more tightly
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Carbon Allotropes
• contrasting properties– hardness
• strong & directional C-C bonds in diamond restrictsthe relative motion between C atoms
• weak van der Waals’ forces between layers of graphite allow the layers to slip over each other
– electrical conductivity• all electrons in diamond are localized• each C atom has a delocalized p-electron to
conduct e- along the same layer
Group IV Oxides
• Formulae of Group IV oxides– C : CO, CO2
– Si : SiO2 only– Ge / Sn / Pb : both XO2 (O.S. +4) & XO (O.S. +2)
Group IV Oxides
• Dissimilarity in properties as illustrated by the following trends down the group :– increasing ionic character
• e.g. variation in m.p. / b.p.
– increasing basic nature• e.g. rxn with H2O (hydrolysis)
– increasing stability of O.S. = +2• e.g. thermal stability of divalent / tetravalent oxides
Variation in m.p. / b.p.
• increasing ionic character (or decreasing covalent character) as illustrated by the variation in m.p./ b.p.– CO / CO2 : simple molecule– SiO2 / GeO2 : giant covalent network– SnO2 / PbO2 : ionic structure
• [02-1-3c, 04-1-7a(ii), 04-AS-6, 95-AS-12b]
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Reaction with Water
• increasing basic nature as illustrated by rxn with H2O (hydrolysis)– CO : neutral � no rxn– CO2 : acidic � react with water & alkali