Classes of Silicate structures

Question 1

What are the 3 classes of silicate structures?

Answer 1

1. ) discrete anions
2. ) One dimensional chains
3. ) Two Dimensional sheets
4. ) Framework silicates

Question 2

What are examples of discrete anions (silicate structure)

Answer 2

Zircon ZrSiO4
Olivine M2SiO4 (M= Mg (2+), Fe(2+))
Beryl (ring structure) Be3Al2Si6O18

Question 3

What are one dimensional chains (silicate structure)

Answer 3

• the simplest chain
• involves the sharing of two O atoms per SiO4 unit
• each SiO4 has two terminal O atoms
• so the repeat unit of the chain is SiO3 (2-)
  cations Na+ and Al3+ balance the charge

Question 4

what cations balance the charge of one dimensional chains (silicate structure)

Answer 4

Na+ and Al3+

Question 5

What happens when two chains link laterally into a ribbon, what is the most common repeating unit?

Answer 5

Si4O11 (6-)

Question 6

what is the purpose of metal ions that bind to the polyionic ribbons together?

Answer 6

to form neutral sheaths

Question 7

why are these polyionic ribbon sheeths occur in fibrous strands (as in the family of asbestos minerals)

Answer 7

due to the weak intermolecular forces

Question 8

What are two dimensional sheets?

Answer 8

• if 3 of the O atoms of each SiO4 unit are shared then INFINITE SERIES are formed.
• only one O atom per SiO4 unit is terminal and carries a negative charge
• all the terminal O atoms point in one direction one the same side of the sheet
• silicate repeat unit: Si2O5 (2-)

Question 9

what is the repeat unit of 2 dimensional sheets

Answer 9

Si2O5(2-)

Question 10

what is the repeat unit of one dimensional chains?

Answer 10

SiO3 (2-)

Question 11

what is the sheet formula of Talc

Answer 11

Mg3(Si2O5)2(OH)2

Question 12

true or false; all the bonding interactions among the ions and atoms of talc occur in a single layer

Answer 12

true

Question 13

how are the layers of talc sheets attracted to each other?

Answer 13

van der waals interactions (intermolecular attractions)

Question 14

what is the significance of each Talc layer being held by van der waals forces with each other?

Answer 14

allows the layers to slip over the other easily and hence talc feels slippery

Question 15

how are aluminosilicates formed?

Answer 15

if some Si atoms in silicates are replaced by Al atoms (plus an appropriate cation)

Question 16

what is the most abundant aluminosilicate

Answer 16

feldspars eg. albite (NaAlSi3O8)

Question 17

true or false, mica is also an aluminosilicate

Answer 17

true

Question 18

how are Al ions and other ions arranged in micas

Answer 18

they lie between aluminosilicate double layers

Question 19

what is theformula of muscovite mica

Answer 19

KAl2(AlSi3O10)(OH)2

Question 20

why do mica sheets not slide over each other so readily as in talc?

Answer 20

there is an ionic component to the interactions between the double sheets

Question 21

true or false; mica can still be cleaved into layers

Answer 21

true

Question 22

how is clay produced?

Answer 22

by weathering of silicate minerals such as talc and micas

Question 23

what structure do clay usually have?

Answer 23

sheet structures with the layers held together by ionic interactions and hydrogen bonds

Question 24

what happens when water is added to clay?

Answer 24

it causes the layers to SWELL and different cations can be found between the layers

Question 25

what is a typical clay material

Answer 25

montmorillonite

Question 26

In framework silicates the SiO4 units share how many oxygen atoms

Answer 26

4 Oxygen atoms

- to give a 3D framework silicate eg. silica (SiO2)

Question 27

what does silica occur naturally as

Answer 27

SiO2 occurs naturally as quartz

Question 28

what does granite consist of?

Answer 28

micro crystals of feldspar, mica and quartz

Question 29

What are zeolites?

Answer 29

• 3 dimensional aluminosilicates
• the negative charge on the aluminosilicate framework is balanced by G1 or 2 cations
• usually open, porous structure with tunnels and channels (4-20A in diameter)
• found in nature but can also be made synthetically
• useful catalysts and absorbants

Question 30

structure of zeolite

Answer 30

porous, open, tunnels and channels (4-20 A in diameter)

Question 31

what are zeolites useful for?

Answer 31

catalysts and absorbants