Silicates:

A class of minerals based on silicon-oxygen units.

SiO 2 Si O

SiO 2 Si O 3-dimensional structure of SiO 4 units

4- Orthosilicate ion, [SiO 4 ] 4-

4- Orthosilicate ion, [SiO 4 ]

4- Orthosilicate ion, [SiO 4 ]

4- Orthosilicate ion, [SiO 4 ]

4- Orthosilicate ion, [SiO 4 ] Forms minerals when combined with various metal counter-ions.

4- Orthosilicate ion, [SiO 4 ] Forms minerals when combined with various metal counter-ions. [Mg 2+ ] 2

Mg 2 SiO 4 Forsterite

Put two tetrahedra together

Si 2 O 7 6- Disilicates

Si 2 O 7 6- Disilicates

Si 2 O 7 6- O’s above Si removed Disilicates

Si 2 O 7 6- O’s above Si removed Disilicates O 7 x –2 = -14 Si 2 x +4 = 8

Ilvaite

Beryl Be 3 Al 2 Si 6 O 18

Beryl

6 tetrahedra in ring

Beryl 6 tetrahedra in ring 2 shared corner/tetrahedra

Beryl 6 tetrahedra in ring 2 shared corner/tetrahedra each share = 1/2 O/Si

Beryl 6 tetrahedra in ring 2 shared corner/tetrahedra each share = 1/2 O/Si 6x2 unshared O = 12 O

Beryl 6 tetrahedra in ring 1 shared corner/tetrahedra each share = 1/2 O/Si 6x2 unshared O = 12 O 12 shared O = 6 O

Beryl 6 tetrahedra in ring 2 shared corner/tetrahedra each share = 1/2 O/Si 6x2 unshared O = 12 O 12 shared O = 6 O Si 6 O 18 Be 3 Al 2 Si 6 O 18

Beryl 6 tetrahedra in ring 2 shared corner/tetrahedra each share = 1/2 O/Si 6x2 unshared O = 12 O 12 shared O = 6 O Si 6 O 18 SiO 3 2-

Talc

6 tetrahedra

Each shares 3 corners

6 tetrahedra Each shares 3 corners Each share = 1/2 O/Si

6 tetrahedra Each shares 3 corners Each share = 1/2 O/Si 6x3= 18 shared

6 tetrahedra Each shares 3 corners Each share = 1/2 O/Si 6x3= 18 shared = 9 O

6 tetrahedra Each shares 3 corners Each share = 1/2 O/Si 6x3= 18 shared = 9 O 6 unshared

6 tetrahedra Each shares 3 corners Each share = 1/2 O/Si 6x3= 18 shared = 9 O 6 unshared Si 6 O 15

6 tetrahedra Each shares 3 corners Each share = 1/2 O/Si 6x3= 18 shared = 9 O 6 unshared Si 6 O 15 Si 2 O 5 2-

quartz

Tetrahedra share all corners

quartz Tetrahedra share all corners Each share = 1/2 O/Si

quartz Tetrahedra share all corners Each share = 1/2 O/Si 4/2 O/Si

quartz Tetrahedra share all corners Each share = 1/2 O/Si 4/2 O/Si SiO 2

Infinite chain

Each tetrahedra shares 2 corners

Infinite chain Each tetrahedra shares 2 corners Each Si has 2 unshared O

Infinite chain Each tetrahedra shares 2 corners Each Si has 2 unshared O 2 shared O = 1 O

Infinite chain Each tetrahedra shares 2 corners Each Si has 2 unshared O 2 shared O = 1 O 3 O/Si

Infinite chain Each tetrahedra shares 2 corners Each Si has 2 unshared O 2 shared O = 1 O 3 O/Si SiO 3

Infinite chain Each tetrahedra shares 2 corners Each Si has 2 unshared O 2 shared O = 1 O 3 O/Si SiO 3 2-

Infinite double chain

4 tetrahedra

Infinite double chain 4 tetrahedra 2 have 2 shared corners

Infinite double chain 4 tetrahedra 2 have 2 shared corners 2 have 3 shared corners

Infinite double chain 4 tetrahedra 2 have 2 shared corners 2 have 3 shared corners SiO 3

Infinite double chain 4 tetrahedra 2 have 2 shared corners 2 have 3 shared corners SiO 3 SiO 2.5

Infinite double chain 4 tetrahedra 2 have 2 shared corners 2 have 3 shared corners SiO 3 x 2 = Si 2 O 6 SiO 2.5 x 2 = Si 2 O 5

Infinite double chain 4 tetrahedra 2 have 2 shared corners 2 have 3 shared corners SiO 3 x 2 = Si 2 O 6 SiO 2.5 x 2 = Si 2 O 5

Infinite double chain 4 tetrahedra 2 have 2 shared corners 2 have 3 shared corners SiO 3 x 2 = Si 2 O 6 SiO 2.5 x 2 = Si 2 O 5 Si 4 O 11 6-

Mg 3 (Si 4 O 10 )(OH) 2

Talc

Magnesium is octahedrally coordinated to 4 Si-Os and 2 OH - s

Magnesium is octahedrally coordinated to 4 Si-Os and 2 OH - s Mg OH O O O O

Mg 3 (Si 4 O 10 )(OH) 2

Mg OH O O O O

Mg 3 (Si 4 O 10 )(OH) 2 Mg OH O O O O Weak forces

Graphite Structure Bonds - strong attraction van der Waal’s forces- weak attraction

Replace an Si with Al and add K to balance charge Mica Mg 3 (Si 4 O 10 )(OH) 2 talc

Replace an Si with Al and add K to balance charge Mica Mg 3 (Si 4 O 10 )(OH) 2 talc KMg 3 (AlSi 3 O 10 )(OH) 2 mica

Replace an Si with Al and add K to balance charge KMg 3 (AlSi 3 O 10 )(OH) 2 K Mg SiO 4 /AlO 4 units Mica

Replace an Si with Al and add K to balance charge KMg 3 (AlSi 3 O 10 )(OH) 2 K Mg SiO 4 /AlO 4 units Mica Mg octahedrally coordinated to six Os.

Mg OH O O O O Mg O O O O O O Stronger Mg – SiO 4 bonding.

Replace an Si with Al and add K to balance charge KMg 3 (AlSi 3 O 10 )(OH) 2 K Mg SiO 4 /AlO 4 units Mica K + O bonds are weak, leading to easy cleavage along O-layer.

Zeolites:

Another type of aluminosilicate.

Si/Al O M x D y (Al x+2y Si n-x-2y O n ).mH 2 O M usually K + ;D group II

M x D y (Al x+2y Si n-x-2y O n ).mH 2 O M usually K + ;D group II

The physical properties of the various zeolites are of more interest than their chemical properties.

Zeolites have openings of a variety of shapes and sizes.

Zeolites have openings of a variety of shapes and sizes. These openings allow zeolites to be used to absorb particular molecules and to be used as molecular sieves.

Zeolites can be used as absorbants for particular molecules.

Zeolites are useful for the separation of small molecules.

Clathrates

Cage-like frameworks of metals with other metals occupying the cavities of the cages.

Clathrates These can be synthesized by mixing finely divided quantities of the metals in the correct proportions and careful heating and cooling.

5 membered rings

5 + 6 membered rings

Clathrates of this type have useful thermal and semiconductor properties.

Clathrates of this type have useful thermal and semiconductor properties. A good semiconductor that has poor thermal conductivity is useful for making a thermo-electric device.

Thermo-electric cooler

Holes and electrons carry energy electrically.

Thermo-electric cooler Holes and electrons carry energy electrically. Electrical energy is converted to heat.

Thermo-electric cooler Holes and electrons carry energy electrically. Electrical energy is converted to heat. Poor thermal conductivity of semiconductor keeps heat from returning to cooling site.

Ceramics and glass

quartz

Each O bonds to 2 Si

quartz Each O bonds to 2 Si Each Si bonds to 4 O

quartz Each O bonds to 2 Si Each Si bonds to 4 O SiO 2

Glass Na 2 O. CaO. (SiO 2 ) 6

Glass Na 2 O. CaO. (SiO 2 ) 6 Approximate formula

Quartz: crystalline, long-range order

glass: short-range order but not crystalline

glass: short-range order but not crystalline All Si bound to 4 O

glass: short-range order but not crystalline All Si bound to 4 O Many O are ‘terminal’

glass: short-range order but not crystalline All Si bound to 4 O Many O are ‘terminal’

glass: short-range order but not crystalline All Si bound to 4 O Many O are ‘terminal’ Ratio of O/Si Is > 2.

glass: short-range order but not crystalline All Si bound to 4 O Many O are ‘terminal’ Ratio of O/Si Is > 2. Si x O y cluster is anionic

glass: short-range order but not crystalline Si x O y cluster is anionic Na + and Ca 2+ balance charge of anion

Properties of glass vs. quartz.

Glass has a lower melting point

Properties of glass vs. quartz. Glass has a lower melting point Glass is softer Glass does not crystallize – this makes it easier to shape it as it cools to a solid form.

Special glasses:

Borosilicate glass

Replace some of the Si sites with B

Borosilicate glasses have lower coefficients of expansion than soda-lime glasses.

Borosilicate glasses have lower coefficients of expansion than soda-lime glasses. Most materials expand when heated.

The coefficient of expansion is a factor, which when multiplied by the temperature change, gives the amount a material will expand or contract.

Since glasses are quite brittle, they are less likely to break when the temperature changes if they have a relatively low coefficient of expansion.

Borosilicate glasses have higher melting points than soda-lime glasses.

Borosilicate glasses have higher melting points than soda-lime glasses. Soda-lime glasses can be melted using a flame generated from methane and air.

Borosilicate glasses have higher melting points than soda-lime glasses. Soda-lime glasses can be melted using a flame generated from methane and air. It is necessary to use a methane/oxygen flame to work borosilicate glass.

Cements:

Portland cement is a specifically formulated powder.

Cements: Portland cement is a specifically formulated powder. When mixed with the proper amount of water it first forms a slurry which flows and can be formed.

When mixed with the proper amount of water it first forms a slurry which flows and can be formed. The slurry hardens and gains strength by the growth of a network of silicate crystals.

(CaO) 3. Al 2 O 3(s) + 3 (CaSO 4. 2 H 2 O) (s) + 26 H 2 O (CaO) 3. Al 2 O 3. (CaSO 4 ) 3. 32H 2 O (s)

(CaO) 3. Al 2 O 3(s) + 3 (CaSO 4. 2 H 2 O) (s) + 26 H 2 O (CaO) 3. Al 2 O 3. (CaSO 4 ) 3. 32H 2 O (s) exothermic

(CaO) 3. Al 2 O 3(s) + 3 (CaSO 4. 2 H 2 O) (s) + 26 H 2 O (CaO) 3. Al 2 O 3. (CaSO 4 ) 3. 32H 2 O (s) exothermic Cooling should favor the formation of products.

6 (CaO) 3. SiO 2(s) + 18 H 2 O (l) (CaO) 5. (SiO 2 ) 6. 5H 2 O (s) + 13 Ca(OH) 2(s)

6 (CaO) 3. SiO 2(s) + 18 H 2 O (l) (CaO) 5. (SiO 2 ) 6. 5H 2 O (s) + 13 Ca(OH) 2(s) crystals

6 (CaO) 3. SiO 2(s) + 18 H 2 O (l) (CaO) 5. (SiO 2 ) 6. 5H 2 O (s) + 13 Ca(OH) 2(s) crystals If the mixture is allowed to dry too rapidly, sufficient water and time will not be available for crystal growth.