Chemical Bonding

Question 1

What do material properties depend on?

Answer 1

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

Question 2

What is crystal structure?

Answer 2

The arrangement of atoms at the
microscopic level

Question 3

Microstructure

Answer 3

Spatial arrangement of different phases

Question 4

What is defect population linked to?

Answer 4

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

Question 5

What factors could be affected in an operating environment

Answer 5

Temperature, Chemical Activity, and Pressure.

Question 6

Define atom

Answer 6

Basic unit of chemical element

Question 7

What is inter-atomic bonding governed by?

Answer 7

The electron structure of the atoms (particularly valence electrons)

Question 8

Name two models covered in class that explain the atomic structure

Answer 8

Bohr atomic model and the wave-mechanical model

Question 9

What are the three characteristics of the Bohr atomic model?

Answer 9

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

Question 10

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

Answer 10

• Electrons are described by four
  quantum numbers

Question 11

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

Answer 11

Electrons exhibit both wave and
particle behavior

Question 12

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

Answer 12

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

Question 13

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

Answer 13

Valence electron structures

Question 14

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

Answer 14

Alkaline earth metals readily donate electrons and are electropositive.

Halogens readily accept electrons and are electronegative.

Question 15

When do atoms accept electrons more readily?

Answer 15

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

Question 16

What is the trend of electronegativity across the periodic table?

Answer 16

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

Question 17

What is the difference between primary and secondary bonds?

Answer 17

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

Question 18

What are the three primary bonds?

Answer 18

Ionic bonds, covalent bonds, and metallic bonds.

Question 19

What are the types of secondary bonds?

Answer 19

Van der Waals bonds and hydrogen bonds.

Question 20

Where are ionic bonds found?

Answer 20

In compounds of metals and non-metals

Question 21

How does electron transfer in ionic bonds work?

Answer 21

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

Question 22

Is the ionic bond directional or non-directional?

Answer 22

Ionic bonds are non-directional

Question 23

Describe the relative bonding energies of ionic bonds.

Answer 23

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

Question 24

Where are covalent bonds found?

Answer 24

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

Question 25

Do covalent bonds share or transfer valence electrons?

Answer 25

They share valence electrons.

Question 26

What properties have a wide range regarding covalent bonds?

Answer 26

* Wide range in bonding energies, melting temperatures and mechanical properties

Question 27

Is the covalent bond directional or non-directional?

Answer 27

* Directional bond

Question 28

What is the strength and rigidity of diamond attributed to?

Answer 28

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

Question 29

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

Answer 29

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

Question 30

Why is graphite soft and ductile?

Answer 30

Because the hexagonal sheets are held by weak secondary bonds.

Question 31

Where are metallic bonds found?

Answer 31

In metals and their alloys

Question 32

Why do metals have excellent electrical and thermal conductivity?

Answer 32

Because they have freely moving electrons.

Question 33

How do metallic bonds form?

Answer 33

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

Question 34

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

Answer 34

* Non-directional bond

Question 35

Describe the relative bonding energies of metallic bonds.

Answer 35

* Range of bond energies

Question 36

Where does van der Waals bonding exist?

Answer 36

It exists between virtually all atoms or molecules

Question 37

Why does van der Waals bonding occur?

Answer 37

Due to random fluctuations in polarization.

Question 38

What is polarization?

Answer 38

Spatial arrangement of electrons in the atom

Question 39

What is the weakest type of secondary bonding?

Answer 39

Van der Waals bonding

Question 40

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

Answer 40

Low bond energies of 4- 30 kJ/mol

Question 41

What are hydrogen bonds?

Answer 41

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

Question 42

How does hydrogen bonding affect DNA?

Answer 42

Hydrogen bonding governs interactions between nitrogenous bases in DNA

Question 43

What is the strongest type of secondary bonding?

Answer 43

Hydrogen bonding

Question 44

Why does hydrogen bonding occur?

Answer 44

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

Question 45

What are the 5 bonding controls?

Answer 45

* Stiffness * Melting temperature * Density * Thermal and Electrical Conductivity * Coefficient of Thermal Expansion

Question 46

What primary bonds are present in metals?

Answer 46

Metallic bonding

Question 47

What primary bonds are present in polymers?

Answer 47

Covalent bonding

Question 48

What primary bonds are present in ceramics?

Answer 48

Ionic and covalent bonding

Question 49

What correlation is consistent within a bond type?

Answer 49

A correlation between bond energy and melting temperature.

Question 50

What is the thermal expansion coefficient?

Answer 50

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

Question 51

Which type of materials have lower expansion coefficients?

Answer 51

The more strongly bonded, higher-melting point materials.

Question 52

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

Answer 52

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

Question 53

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

Answer 53

Percent ionic character depends on the atoms' electronegativity.

Question 54

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

Answer 54

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

Question 55

What does non-directional mean?

Answer 55

The magnitude is equal in all directions around an ion

Question 56

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

Answer 56

- Secondary atomic bonding - Geometry of primary atomic bonding

Question 57

Why can geckos cling to any surface?

Answer 57

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