Structural - lecture 3

Question 1

What is the equation for the volume of a sphere?

Answer 1

4/3 πr3

Question 2

Which type of arrangement do atoms mostly have?

Answer 2

Close packed arrangement

Question 3

How many tetrahedral and octahedral holes are there per close-packed sphere?

Answer 3

2 Tetrahedral

1 octahedral

Question 4

What is the maximum size for small spheres to fit into the holes without disrupting the close packing of the larger spheres for octahedral?

Answer 4

r oct = 0.414 Rᶜᵖ

Question 5

What is the maximum size for small spheres to fit into the holes without disrupting the close packing of the larger spheres for tetrahedral?

Answer 5

r tet = 0.225 Rᶜᵖ

Question 6

What happens when the ratio of R+/R- increases?

Answer 6

More anions will be able to fit around one cation

Question 7

What are the characteristics for a molecule with cubic geometry?

Answer 7

Co-ordination number is 8

R+/R- = 1.000 to 0.732

Question 8

What are the characteristicsfor a molecule with octahedral geometry?

Answer 8

Co-ordination number is 6

R+/R- = 0.732 to 0.414

Question 9

What are the characteristics for a molecule with tetrahedral geometry?

Answer 9

Coordination number is 4

R+/R- = 0.414 to 0.225

Question 10

What are the characteristics for a molecule with trigonal planar geometry?

Answer 10

Co-ordination number is 3

R+/R- = 0.225 to 0.155

Question 11

What are the characteristics of a molecule with linear geometry?

Answer 11

Co-ordination number is 2

R+/R- is 0.155 downwards

Question 12

What is R+/R-?

Answer 12

The ratio of anions to cations

Question 13

What are the most common co-ordination shapes?

Answer 13

Tetrahedral and octahedral

Question 14

Why will 2 tetrahedra never share three corners?

Answer 14

Because that brings te two cations too close to each other

Question 15

Can octahedra share faces?

Answer 15

Unlike tetrahedra, yes

Question 16

What happens when polyhedra are linked together by sharing corners?

Answer 16

Larger units which may be discrete are formed or they may be polymeric structures

Question 17

What happens to many metals that are close packed under normal conditions when they are under higher temperatures?

Answer 17

When heated, they will lean towards the less efficiently packed body centred cubic structure

Question 18

What are the three different types of model?

Answer 18

Ball and spoke
Close-packed spheres
Linked polyhedra