Group 14

1. Group 14 C Nonmetal Si & Ge Metalloids Sn & Pb Metals • Carbon has multiple allotropes • The nonmetals and metalloids can take on multiple oxidation states, but don’t tend to form ions • The metals Sn and Pb can form +2 or +4 cations • Four valence electrons: [N.G.] ns2 np2

2. Carbon • - The chemistry of carbon is so diverse it forms its own subdicipline of organic • chemistry • - There are three main allotropes of carbon: • i) Graphite, a network solid • ii) Diamond, a network solid • iii) Fullerenes, most commonly C60 (buckminsterfullerene – the “bucky ball”)

3. Graphite • - lubricant because, while the atoms within a layer are tightly bonded the layers themselves are held together loosely. • conduct electricity and is used to make electrodes in batteries and for electrolysis. • - Stable at extremely high temperatures at which it remains solid mean that it is also useful in many high temperature environments (e.g. furnaces). • - The 2-D layered structure of graphite makes it relatively soft and • flaky, the three-dimensional network structure of diamond • makes it the hardest substance known. It’s therefore useful to make • drill bits and abrasives. • - Fullerenes are hollow molecules made up of 5- and 6-carbon rings .

4. Oxides of Carbon • Like the oxides of the other nonmetals, they are acidic: • Draw the Lewis structure of carbon monoxide. What is unusual about • it? For this reason, carbon monoxide is an excellent Lewis base – so much so that it can bond to iron cations in hemoglobin, preventing oxygen transport:

5. Silicon • - Silicon is the second most abundant. • Silicon dioxide (“silica”) does not exist as discrete • molecules. What must its structure be like? • Silica is a very common and useful compound • Sand and quartz are both forms of silica. • Silica that has been melted and resolidified • without being allowed to crystallize is glass • (an amorphous solid). • Silica is weakly acidic, slowly dissolving in • strong bases: Beta quartz Alpha quartz Glass

6. Tin and Lead • As the two metals in Group 14, tin and lead have significantly lower melting • points than carbon, silicon and germanium. • Tin and lead can both form cations. What are the electron configurations of the • two tin cations? Why is Sn3+ not feasible? • Many compounds of tin and lead are highly toxic; however, while elemental • lead is toxic, elemental tin is not. In fact, tin is an essential element (in the right • form).

7. α-BN, hexagonal α-BN, hexagonal α-BN, hexagonal Boron Revisited • Boron is the only element in Group 13 that is not a metal. Sometime referred to • as a nonmetal, as it a semi-conductor it is strictly speaking a metalloid • Boron does not react with oxygen, water, acids or bases. • In crystalline form, boron is one of the hardest substances on Earth. Scoring • 9.3 on the Mohs scale of hardness, crystalline boron can scratch most • substances other than diamond (which scores a perfect 10). • Ceramic made with B and N very strong and heat resistant materials. • BN –hexagonal • Same as graphite • Mohs :1-2 β-BN, sphalerite structure Same as diamond Mohs : 10 w -BN, wurtzite structure Mohs :10

8. Boron Revisited • We have already seen a few boron-containing compounds in CHEM 1000: • Each of these compounds is an excellent Lewis acid. Why?

9. Boron Revisited • Pure borane (BH3) has never been isolated. It is presumably a good Lewis • acid because if borane is made in a solvent that is a good Lewis base, a • Lewis acid-base complex forms: • If borane is made without another Lewis base present, it undergoes a • Lewis acid-base reaction with itself. The simplest example of this reaction • gives diborane (B2H6):

10. Boron Revisited • There are only 6 valence electrons in B2H6, but it looks like there are 4 • bonds. • In two of the bonds 3 atoms are sharing a pair of electrons. • The 2 central hydrogen atoms are each part of a three-atom two-electron • bondwith both boron atoms • Why is one B2H6 more stable than two BH3 molecules?