Structure and bonding in solids

Question 1

what are the two categories solids are divided into?

Answer 1

amorphous solids

crystalline solids

Question 2

What does amorphous solid mean?

Answer 2

• poorly defined shapes

- lack molecular ordering particles

Question 3

What does crystalline solid mean?

Answer 3

• well defined shape

- because particles (atoms, ions, molecules) are precisely ordered

Question 4

How are the particles in a crystal packed

Answer 4

tightly

in an orderly 3D array

Question 5

what shape are the particles considered as?

Answer 5

spheres

Question 6

the centre point of each sphere form a regular pattern throughout the crystal called….

Answer 6

crystal lattice

Question 7

true or false; each lattice point has identical surroundings (view from each lattice point is the same)

Answer 7

true

Question 8

What is the lattice which has the highest possible symmetry?

Answer 8

cubic system

Question 9

How is the cubic system lattice obtained?

Answer 9

by filling space with a series of identical cubes;

the unit cells of the system

Question 10

What does a single unit cell contain?

Answer 10

all the structural information about the crystal

Question 11

true or false; a crystal could be constructed in principle by making a great many copies of a single unit cell and stacking them together.

Answer 11

true

Question 12

How many types of 3D lattice can be formed and why?

Answer 12

7 types

- due to the symmetry constraints

Question 13

What is the shape of the unit cells of each of the 7 types of 3D lattices?

Answer 13

parallelepiped

Question 14

true or false; the unit cell is the smallest unit; that if repeated in all 3 directions gives an entire unit structure

Answer 14

true

Question 15

what are the smallest unit cells called?

Answer 15

primitive unit cell

Question 16

true or false; the corners of each unit cell is shared by seven other unit cells

Answer 16

true

- a total of one lattice point per unit cell

Question 17

What describes the primitive unit cells fully?

Answer 17

3 edge lengths

three angles between those edges

Question 18

what happens when when the primitive unit cell does not have all the symmetry elements in the crystal?

Answer 18

a larger non-primitive unit cell with all the appropriate symmetry elements is then chosen

Question 19

in practice where are cubic lattices mostly found in?

Answer 19

metallic elements (mostly)

• some covalent compounds
• many ionic compounds

Question 20

What are the 3 types of unit cells within the cubic system?

Answer 20

simple cubic unit cell
body centered cubic unit cell
face centered cubic unit cell

Question 21

is the simple cubic unit cell a type of primitive unit cell?

Answer 21

yes

Question 22

true or false; bcc and fcc unit cells are also examples of primitive unit cells?

Answer 22

no; false

- they are examples of non-primitive unit cells

Question 23

what is the coordination number of each particle in a simple cubic unit cell?

Answer 23

6

Question 24

What is the coordination number of each particle in a bcc unit cell?

Answer 24

8

Question 25

What is the coordination number of each particle in a fcc unit cell?

Answer 25

12

Question 26

true of false; for bcc the corner particles do not touch each other, rather they all touch the centre sphere

Answer 26

true

Question 27

true or false; for fcc a particle lies at each corner and at the centre of each face but not in the centre of the cube

Answer 27

true

Question 28

true or false; for fcc the particles at the corners touch those in the faces but not each other

Answer 28

true

Question 29

how are unit cells placed?

Answer 29

they lie adjacent to each other throughout the crystal WITH NO GAPS

Question 30

why does each corner of a unit cell make only 1/8 contribution to each unit cell

Answer 30

a particles at the corner is shared by 7 other unit cells in the lattice

Question 31

why is a particle found at the face of a unit cell only make 1/2 of contribution to the unit cell?

Answer 31

because a particle on the face is shared by one other unit cell in the lattice

Question 32

how many atoms does a simple cubic unit cell have? (be able to calculate)

Answer 32

1

Question 33

how many atoms does a bcc unit cell have? (be able to calculate)

Answer 33

2

Question 34

how many atoms does a fcc unit cell have?

Answer 34

4

Question 35

how much does an edge particle contribute to the unit cell?

Answer 35

1/4

Question 36

true or false; the higher the coordination number of the particles in the crystal the greater the number of particles per volume (the more efficient the packing)

Answer 36

true