230709 - Structure Of Matter (P1-C1)

Question 1

Generally, the physical, mechanical and chemical properties of any material depend on

Answer 1

1. Atomic structure
2. Inter-atomic bonding
3. Arrangement of atoms in space

Question 2

Atom consists of

Answer 2

1. Positive central nucleus
2. Negative peripheral electrons

Question 3

Electrical state of atom

Answer 3

Neutral

Question 4

What is atomic number?

Answer 4

Number of electrons

Question 5

What is valence electrons?

Answer 5

• electrons in the outer most shell
• Determines the chemical reactivity of the element

Question 6

What is the atomic weight?

Answer 6

Protons + neutrons

Question 7

How many electrons in the outer shell of an atom should have to achieve a stable state?

Answer 7

8 electrons

Question 8

How can we obtain a stable state atom?

Answer 8

1. receive electrons
2. Release electrons
3. Share electrons

Question 9

Three types of primary bonds

Answer 9

1. Ionic bond
2. Covalent bond
3. Metallic bond

Question 10

What is a ionic bond?

Answer 10

• involving electron transfer
• Attraction of positive and negative ions occurred

Question 11

Sodium chloride is an example of which primary bond?

Answer 11

Ionic bond

Question 12

Glasses in ceramics containing what type of primary bond?

Answer 12

Ionic bond

Question 13

Characteristics of ionic solids

Answer 13

1. High thermal resistance
2. High strength and hardness
3. Insoluble in organic solvents
4. Soluble in ionized solvents (water)

Question 14

What is covalent bonds?

Answer 14

Sharing of electrons

Question 15

Diamonds and polymers containing which type of primary bond?

Answer 15

Covalent bond

Question 16

Characteristics of covalent bonds

Answer 16

1. Insoluble in water
2. Very strong and hard
3. Can withstand high temperature (insulator)
4. Directional (electrons spend most of their time in the region, where the orbit overlap)

Question 17

What is metallic bond?

Answer 17

• Attraction between positive cores and free electrons or electron cloud
• in metal

Question 18

Characteristics of the metallic bonds

Answer 18

1. High thermal and electrical conductivity
2. High strength and hardness
3. Opacity (absorption of light by the free electrons)
4. Lustrous (free electrons reemit the light)
5. Malleable (can be hammered into thin sheets without fracture)
6. Ductile (can we drive into thin wires)

Question 19

Two types of formation of electrical dipoles in secondary bonds

Answer 19

1. Fluctuating dipole
2. Permanent dipole

Question 20

What is fluctuating dipole?

Answer 20

• more electrons on one side of the nucleus than the other
• Asymmetry electrons distribution
• Causing weak attractive forces between the fluctuating dipole in joining atoms

Question 21

What is permanent dipole?

Answer 21

• Example: hydrogen bond
• Electrons around oxygen nucleus are more than those around the hydrogen nucleus
• Positive hydrogen and negative oxygen will cause weak attractive force

Question 22

Characteristics of secondary bonds

Answer 22

1. Low strength and hardness
2. Low thermal resistance

Question 23

Factors of spacing of solid atoms

Answer 23

1. Forces of attraction
2. Forces of repulsion

Question 24

Factors affecting inter-atomic distance

Answer 24

1. Number of adjacent atoms (-ve)
2. Effect of temperature (+ve)
3. Type of bond (primary>secondary)
4. External force application (increase tensile stress)

Question 25

Classification of solids according to the type of bond between atoms

Answer 25

1. Atomic solid 2. Molecular solid

Question 26

Difference between atomic solid and molecular solids

Answer 26

Atomic solid 1. Primary bond exists between the atoms and molecules 2. High strength and hardness Molecular solid 1. Primary bond between atoms, but secondary bond between the molecules 2. No strength and hardness

Question 27

Classification of solids, according to arrangement of atoms

Answer 27

1. Crystalline solids 2. Amorphous solid

Question 28

What is space lattice?

Answer 28

Regular arrangement of atoms in space

Question 29

How many types of space lattice exist

Answer 29

About 14 but only few of dental interest

Question 30

What is unit cell?

Answer 30

The smallest repeating unit in the space lattice

Question 31

Unit cells are classified according to

Answer 31

1. Length of axes (a,b,c) 2. Interfacial angle (alpha beta gamma)

Question 32

Types of cubic system

Answer 32

1. Simple cubic system (S.C.) 2. Body centered cubic (B.C.C) 3. Face centered cubic (F.C.C.)

Question 33

Formula of atomic packing factors

Answer 33

Atomic packing factors = volume of atoms inside the unit cell / volume of unit cell ^ APF ^ density ^ strength properties

Question 34

What is the meaning of amorphous?

Answer 34

Without shape

Question 35

Difference between crystalline and amorphous solids

Answer 35

Crystalline solids 1. Definite melting point 2. Regular unit cell with repetition 3. Low internal energy Amorphous solids 1. Melting range 2. No regular unit cell 3. High internal energy

Question 36

What is polymorphism?

Answer 36

Polymorphic materials that can exist with more than one crystal structure by changing the surrounding physical condition, such as silica (SiO2)

Question 37

Forms of silica structure

Answer 37

1. Quartz 2. Tridymite 3. Cristobalite 4. Fused quartz

Question 38

Types of transformations

Answer 38

1. Reconstructive transformation 2. Displacive transformation

Question 39

Difference between reconstructive transformation and displasive transformation

Answer 39

Reconstructive transformation 1. Breakdown atomic bond followed by reconstruction of new space lattice 2. No expansion 3. Slow transformation 4. High temperature needed Displacive transformation 1. No breakdown of atomic bond 2. Expansion occurred 3. Rapid transformation 4. Low temperature

Question 40

Types of crystalline imperfections

Answer 40

1. Point defects 2. Line defects (dislocation: displacement of a row of atoms from their normal position in the lattice) 3. Plane defects