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Materials > Chapter 1: Structure of Matter > Flashcards

Chapter 1: Structure of Matter Flashcards

1
Q

what is the basic unit of any material?

A

atom

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2
Q

Nucleus is the core of the atom and composed of:

A

✓ Positively charged protons.
✓ Uncharged neutrons.

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3
Q

The most outer electrons are cld:

A

valance electrons
& they affect the physical & chemical properties

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4
Q

Atomic number =

A

Number of electrons = number of protons

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5
Q

Atomic weight =

A

weight of protons + neutrons

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6
Q

To reach za configuration of 8 e in an
outer shell by:

A
  • Releasing e ➔ become +ve charged
  • Receiving extra e ➔ become –ve charged
  • Sharing e w/ another atom
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7
Q

list the atomic bonds

A
  1. primary bond
  2. secondary bond
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8
Q

list the primary bonds

A
  1. covalent bond
  2. ionic bond
  3. metallic bond
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9
Q

examples of covalent bonds

A

Basic bond of diamond & polymer

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10
Q

Characteristics of covalent bond:

A
  1. Highly directional bond.
  2. High strength + hardness.
  3. High heat resistance.
  4. Thermal + electrical insulators.
  5. Dissolve in organic solvents.
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11
Q

general info on ionic bond

A

Occurs by e transfer from one atom (become +ve ion) to another (Become –ve ion), then electrostatic attraction b2ian them.

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12
Q

examples of ionic bonds

A

Basic bond for Ceramics, Glasses.

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13
Q

general info on covalent bond

A
  • Arises by sharing e b2ian atoms, the atoms approach one another + orbital overlap happened.
  • It May be same element (e.g. H2) or b2ian different elements (e.g. CH4)
  • It may be single bond, double bond or triple bond
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14
Q

Characteristics of Ionic bond:

A
  1. Spherical in nature.
  2. High strength + hardness.
  3. High heat resistance.
  4. Insulators as solids.
  5. Electric conductors in solutions.
  6. Dissolve in ionizing solvents (not in organic solvents).
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15
Q

general info on metallic bond

A

➢ The metals have loosely held valence e, so they move freely b2ian atoms forming cloud of e.
➢ So, the metallic bond is the attraction between the +ve cores and –ve free electrons.

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16
Q

Characteristics of Metallic bond:

A
  1. High. strength + hardness.
  2. High thermal resistance.
    3.High thermal conductivity
  3. High electric conductivity
  4. Opaque
    6.Lustrous
  5. Leads to crystalline arrangement in metals
  6. Leads to easy of deformability of metals.
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17
Q

GR high thermal conductivity is a characteristic of Metallic bond:

A

as free electrons conduct heat

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18
Q

GR high electric conductivity is a characteristic of Metallic bond:

A

as free electrons carry the electric current

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19
Q

GR Opaque is a characteristic of Metallic bond:

A

as free electrons absorb light

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20
Q

GR Lustrous is a characteristic of Metallic bond:

A

as free electrons reflect the light

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21
Q

types of Secondary bonds (Van der Waals Forces):

A

a. FluctuatingDipole
b. Hydrogen Bond

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22
Q

info on fluctuating dipole:

A

➢develops b2ian atoms due to asymmetry of e distribution.
➢ This asymmetry gives the atom dipole character.
➢ It is a temporary bond.

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23
Q

info on hydrogen bond:

A

➢ develops b2iann molecules when each molecule has a dipole.
➢Attraction occurs b2ian the +ve part of molecule and -ve part of another molecule.

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24
Q

Characteristics of secondary bond:

A
  1. Low strength and hardness.
  2. Low heat resistance.
  3. High thermal expansion.
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25
Q

interatomic distance results from…

A

2 equal but opposite forces:
i. Repulsive forces➔ due to electrostatic field of each atom.
ii. Attractive forces➔ different types of atomic bonds.

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26
Q

list factors affecting interatomic Distance:

A
  1. Temperature
  2. Number of adjacent atoms
  3. Type of the bond
  4. Any external forces may displace atoms and change I.A.D.
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27
Q

affect of temp. on interatomic distance?

A

Heat ↑ I.A.D (as it ↑ energy of atoms)

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28
Q

affect of no. of adjacent atoms on interatomic distance?

A

More adjacent atoms will ↑ I.A.D (as less specific attraction to any
neighboring atom).

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29
Q

affect of type of the bond on interatomic distance?

A

↑ number of shared e in covalent bond will ↓ I.A.D (as it means stronger bond).

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30
Q

how r solids classified into?

A

I. According to Intermolecular Bond
II. According to Arrangement of Atoms

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31
Q

Bond between atoms =

A

inter-atomic bond = intra-molecular bond

**Must be primary bond

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32
Q

Bond between molecules=

A

inter-molecular bond

**May be primary or secondary

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33
Q

What’s Glass Transition temperature:

A

The temperature at which the amorphous solids start to soften or harden

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34
Q

The smallest repeated unit in a crystal lattice is cld?

A

unit cell

35
Q

Crystalline Solids can be divided into:

A
  1. Cubic System
  2. Hexagonal Crystal
36
Q

info on Cubic System:

A

➢ Axes: a = b = c
➢ Angles between axes: 90 degrees

37
Q

cubic system is subdivided into:

A

a. Simple Cubic System (SC)
b. Body Centered Cubic (BCC)
c. Face Centered Cubic (FCC)

38
Q

info on Hexagonal Crystal

A

➢ Axes: a = b ≠ c
➢ Angles between axes: α = β = 90 degrees
gamma = 120 degrees

39
Q

Hexagonal Crystal is divided into:

A
  • Simple Hexagonal System
  • Hexagonal Closed Packed (HCP)
40
Q

each unit cell contains how many atoms in simple hexagonal system?

A

3 atoms

41
Q

each unit cell contains how many atoms in hexagonal closed packed (HCP)?

A

6 atoms

42
Q

Atomic Packing Factor def:

A

It’s the fraction of space occupied by the atoms

43
Q

Atomic Packing Factor=

A

Volume of atoms inside unit cell / Volume of unit cell

44
Q

Clinical importance of APF:

A

↑ APF ➔ have ↑ densities + strength properties

45
Q

GR Theoretical calculation of strength is much higher than actual strength

A

due to presence of defects in crystalline system.

46
Q

list types of crystalline imperfections:

A

a. Point defect
b. Line defect
c. Plane defect

47
Q

info on Point defect:

A
  1. Vacancy ➔ missing atom within the crystal
  2. Self-interstitial atom➔extra atom from same metal is lodged within crystal.
  3. Interstitial impurity➔ extra atom from another metal is lodged within crystal.
  4. Substitutional impurity➔atom from another metal replaced the space of the
    original atom.
48
Q

info on line defect:

A

➢ The most common type.
➢ Dislocation: it is the displacement of a row of atoms from their normal positions
in the lattice.

49
Q

Clinical importance of line defect

A

plastic deformation in metals occurs by motion of
dislocations

50
Q

info on Polymorphism

A
  • Materials that have the same chemical composition but found naturally in different physical forms.
  • The polymorphic forms have different physical properties as density, freezing point, optical properties, conductivities …etc
51
Q

If the material is inorganic, the polymorphism is cld

A

allotropy

52
Q

If the material is organic, the polymorphism is cld

A

isomerism

53
Q

Silica showed two types of transformation:

A
  1. Displasive transformation: the same form just expanded at low temperature.
  2. Reconstructive form: involves transformation from one form to another.
54
Q

Correlation Between Atomic Structure and Materials Properties:
in Density

A

controlled by ➔ atomic weight, atomic radius, atomic packing factor.

55
Q

Correlation Between Atomic Structure and Materials Properties:
Bond strength leads to:

A

➢ High strength and hardness.
➢ High melting and boiling temperature.
➢ Low coefficient of thermal expansion.

56
Q

Correlation Between Atomic Structure and Materials Properties:
Electrical and Thermal conductivity

A

➔ depends on nature of atomic bond
- Metallic solids conduct heat + electricity.
- Ionic solution conduct electricity, while ionic solids are electrical insulators.
- Covalent solids are insulators.

57
Q

Correlation Between Atomic Structure and Materials Properties:
Crystalline solids

A

have low internal energy bc they send their internal energy in arranging their atoms.

58
Q

GR FCC is more ductile than BCC

A

due to higher atomic packing factor

59
Q

GR FCC is more ductile than HCP

A

due to symmetry of the cubic system

60
Q

GR: Every element tries to complete its outer electronic shell

A

To reach the stable configuration

61
Q

GR: Covalent bond is a highly directional bond

A

Bc the shared electrons occupy a specific direction.

62
Q

GR: Ceramics and glasses have high strength and hardness

A

Bc they formed of primary bond (ionic bond).

63
Q

GR: Ionic compounds conduct electricity in solutions

A

Bc they ionized in solution and ions can carry electricity.

64
Q

GR: Metallic elements conduct heat and electricity.

A

bc free electrons carry heat and electricity

65
Q

GR: Metallic elements are opaque

A

Bc free electrons absorb light so prevent its passage through the material

66
Q

GR: Metallic elements are lustrous

A

bc free electrons reflect the light

67
Q

GR: Metals are malleable and ductile

A

BC they contain dislocations (slip plane)

68
Q

GR: Water molecules are bonded by hydrogen bond

A

BC each molecule has a permanent dipole.

69
Q

GR: Increasing the number of adjacent atoms decrease the interatomic distance

A

Due to less specific attraction to any neighboring atom.

70
Q

GR: Interatomic distance between CH-CH is more than CH=CH

A

BC the higher number of shared electrons

71
Q

GR: Diamond (atomic solids) is stronger than polymer (molecular solids)

A

BC the inter-molecular bonds of diamond are primary bond while they are secondary bond in polymers.

72
Q

GR: Crystalline solids have low internal energy

A

BC they spend their internal energy in arranging their atoms.

73
Q

GR: Metals have definite melting temperature.

A

BC they are crystalline solids

74
Q

GR: Wax have glass transition temperature

A

BC they are amorphous solids

75
Q

GR: Amorphous solids have high internal energy

A

BC their atoms are randomly distributed

76
Q

GR: Simple cubic system contains one atom per unit cell

A

BC it has 1/8 atom at each corner (1/8 X 8 = 1 atom).

77
Q

GR: Body centered cubic system contains two atoms per unit cell

A

BC it has 1/8 atom at each corner + one atom at the center of the unit cell (1/8 X 8 + 1 = 2 atoms).

78
Q

GR: Face centered cubic system contains four atoms per unit cell

A

BC it has 1/8 atom at each corner + 1⁄2 atom at each face (1/8 X 8 + 1⁄2 X 6 = four atoms)

79
Q

GR: Face centered cubic materials have high density than body centered cubic materials

A

Due to higher atomic packing factor of FCC materials

80
Q

GR: Theoretical calculation of the metal strength is much higher than actual strength.

A

Due to presence of crystalline imperfections.

81
Q

GR: Different forms of silica have different physical properties and same chemical properties

A

BC they r allotropic forms (have same chemical structure)

82
Q

GR: Reconstructive transformation requires more time and heat.

A

BC it requires breakdown of the atomic bonds and reconstruction of new bonds w/ different space lattice

83
Q

GR: Face centered cubic system are more ductile than body centered cubic.

A

Due to higher atomic packing factor of FFC

84
Q

GR: Face centered cubic system are more ductile than hexagonal closed pack

A

Due to the symmetry of the unit cell axes of FCC

Materials (2 decks)

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