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APSC 278 (Engineering Materials) > Chemical Bonding > Flashcards

Chemical Bonding Flashcards

1
Q

What do material properties depend on?

A

Chemical composition, crystal structure, microstructure, defect population, operating environment

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2
Q

What is crystal structure?

A

The arrangement of atoms at the
microscopic level

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3
Q

Microstructure

A

Spatial arrangement of different phases

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4
Q

What is defect population linked to?

A

It is linked to manufacturing process
(critical in fatigue, which can arise during cyclic loading)

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5
Q

What factors could be affected in an operating environment

A

Temperature, Chemical Activity, and Pressure.

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6
Q

Define atom

A

Basic unit of chemical element

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7
Q

What is inter-atomic bonding governed by?

A

The electron structure of the atoms (particularly valence electrons)

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8
Q

Name two models covered in class that explain the atomic structure

A

Bohr atomic model and the wave-mechanical model

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9
Q

What are the three characteristics of the Bohr atomic model?

A
  • Electrons revolve around
    nucleus in discrete orbitals
  • Electrons can only have
    specific energy levels
  • Orbitals are separated by
    finite energies
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10
Q

What type of numbers describes electrons in the wave-mechanical model?

A
  • Electrons are described by four
    quantum numbers
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11
Q

What type of behaviour do electrons exhibit in the wave-mechanical model?

A

Electrons exhibit both wave and
particle behavior

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12
Q

What is the position of an electron described by in the wave-mechanical model?

A

The position of an electron is described
as a probability distribution at
various locations around the nucleus.

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13
Q

What do elements in a group (column) have in common/are similar to each other?

A

Valence electron structures

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14
Q

What is the difference between alkaline earth metals and halogens in terms of donating and accepting electrons?

A

Alkaline earth metals readily donate electrons and are electropositive.

Halogens readily accept electrons and are electronegative.

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15
Q

When do atoms accept electrons more readily?

A

When their valence shell is nearly full and when they are less shielded from the nucleus.

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16
Q

What is the trend of electronegativity across the periodic table?

A

Electronegativity increases from left to right and from the bottom to the top across the periodic table.

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17
Q

What is the difference between primary and secondary bonds?

A

Primary bonds are strong while secondary (inter-molecular) bonds are weak.

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18
Q

What are the three primary bonds?

A

Ionic bonds, covalent bonds, and metallic bonds.

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19
Q

What are the types of secondary bonds?

A

Van der Waals bonds and hydrogen bonds.

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20
Q

Where are ionic bonds found?

A

In compounds of metals and non-metals

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21
Q

How does electron transfer in ionic bonds work?

A

Metal atoms (electropositive) give up their valence electron
to the non-metal (electronegative)

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22
Q

Is the ionic bond directional or non-directional?

A

Ionic bonds are non-directional

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23
Q

Describe the relative bonding energies of ionic bonds.

A
  • Bond energies can be strong, between 600-1500 kJ/mol
24
Q

Where are covalent bonds found?

A

In materials whose atoms have small differences in
electronegativity (close to each other in the periodic table)

25
Q

Do covalent bonds share or transfer valence electrons?

A

They share valence electrons.

26
Q

What properties have a wide range regarding covalent bonds?

A
  • Wide range in bonding energies, melting temperatures and
    mechanical properties
27
Q

Is the covalent bond directional or non-directional?

A
  • Directional bond
28
Q

What is the strength and rigidity of diamond attributed to?

A

The tetrahedral structure of carbon atoms (extends infinitely in space)

29
Q

How is graphite arranged and what is it made out of?

A

Graphite is also comprised of carbon atoms, but arranged in
hexagonal sheets that are held weakly by a type of secondary bond.

30
Q

Why is graphite soft and ductile?

A

Because the hexagonal sheets are held by weak secondary bonds.

31
Q

Where are metallic bonds found?

A

In metals and their alloys

32
Q

Why do metals have excellent electrical and thermal conductivity?

A

Because they have freely moving electrons.

33
Q

How do metallic bonds form?

A

Metal atoms give up their valence electron to form a “sea of
electrons” or “electron cloud”

34
Q

What type of bond (non-directional or directional) is a metallic bond?

A
  • Non-directional bond
35
Q

Describe the relative bonding energies of metallic bonds.

A
  • Range of bond energies
36
Q

Where does van der Waals bonding exist?

A

It exists between virtually all atoms or molecules

37
Q

Why does van der Waals bonding occur?

A

Due to random fluctuations in polarization.

38
Q

What is polarization?

A

Spatial arrangement
of electrons in the atom

39
Q

What is the weakest type of secondary bonding?

A

Van der Waals bonding

40
Q

What is the range of bond energies of van der waals bonding?

A

Low bond energies of 4-
30 kJ/mol

41
Q

What are hydrogen bonds?

A

Special type of secondary bond when Hydrogen is
covalently bonded to Oxygen, Nitrogen or Fluorine

42
Q

How does hydrogen bonding affect DNA?

A

Hydrogen bonding
governs interactions
between nitrogenous
bases in DNA

43
Q

What is the strongest type of secondary bonding?

A

Hydrogen bonding

44
Q

Why does hydrogen bonding occur?

A

Due to asymmetric distribution of charge, as a result of
the difference in electronegativities of atoms and their spatial
arrangement

45
Q

What are the 5 bonding controls?

A
  • Stiffness
  • Melting temperature
  • Density
  • Thermal and Electrical Conductivity
  • Coefficient of Thermal Expansion
46
Q

What primary bonds are present in metals?

A

Metallic bonding

47
Q

What primary bonds are present in polymers?

A

Covalent bonding

48
Q

What primary bonds are present in ceramics?

A

Ionic and covalent bonding

49
Q

What correlation is consistent within a bond type?

A

A correlation between bond energy and melting temperature.

50
Q

What is the thermal expansion coefficient?

A

The change in size of a material per degree temperature change.

51
Q

Which type of materials have lower expansion coefficients?

A

The more strongly bonded, higher-melting point materials.

52
Q

What is the relationship between bonding energy, the difficulty of breaking a bond, the energy required to break a bond, and melting temperature?

A

More bond energy = more difficult to break a bond = more energy required to break bond = higher melting temperature

53
Q

What does the percent ionic character of a bond depend on?

A

Percent ionic character depends on the atoms’ electronegativity.

54
Q

For materials of a comparable structure or certain bond type, what is the relationship between melting temperature and the linear expansion coefficient?

A

Inverse relationship; the linear expansion coefficient decreases with increasing melting temperature.

55
Q

What does non-directional mean?

A

The magnitude is equal in all
directions around an ion

56
Q

Graphite is a soft material, while diamond is very hard. What are the key contributing factors that explain these differences?

A
  • Secondary atomic bonding
  • Geometry of primary atomic bonding
57
Q

Why can geckos cling to any surface?

A

Due to the Van der Waals forces that can interact via the tiny hairs.

APSC 278 (Engineering Materials) (30 decks)

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