Week 2 Flashcards
What is the key to understanding matter?
understanding the attractive and interactive forces between atoms
What do different interactions between atoms give rise to?
different classes of materials
What is the major determinant of material properties?
the types of bonds formed between atoms
What are the 3 primary (or stronger) types of bonds?
- ionic
- covalent
- metallic
What is the strongest bond?
ionic bond
When an electron from one element is given completely to another in return for forming the bond
ionic bond
In this type of bond, positive charge attracts a negative charge
ionic bond
What is an example of an ionic bond?
salt
NaCl
In this type of bond, atoms are shared.
covalent bond
True or false: covalent bonds are good conductors of heat and electricity
false
What are two examples of covalent bonds?
- Water (H2O)
- Ammonia (NH3)
In this type of bond, electrons are shared to form a bond and all atoms donate electrons to form an electron cloud.
Metallic bonds
These atoms are good donors of electrons
metals
True or false: Metals are good conductors of heat and electricity.
True
What is an example of a metallic bond?
pack of positive ions surrounded by negative delocalized electrons
Where in the periodic table would you find metal atoms and non metal atoms?
What are the two secondary (weaker) bonds?
- van der Waals
- hydrogen
What are secondary bonds based on?
attraction between atomic or molecular dipoles
This type of bond is between atoms or non-polar molecules that cause a temporary change in dipole moment arising from a brief shift of orbital electrons to one side of one atom or molecule.
van der Waals
This type of bond involves a hydrogen atom located between a pair of other atoms having a high affinity for electrons.
hydrogen bond
**pick up the FON
Are hydrogen bonds stronger than van der waals?
Yes.
Organize the bonds according to their relative strength (weak –> strong)
- van der waals
- ionic
- hydrogen
- metallic
- covalent
- van der waals
- hydrogen
- metallic
- covalent
- ionic
Classify covalent bonds, ionic bonds and metallic bonds as forming either molecules or lattices
- covalent bonds form molecules
- ionic and metallic bonds form lattices
When different elements bond together into a discrete unit
molecules
Covalent bonds commonly form
molecules
What is the molecular weight of molecules?
sum of mass of each atom
What are two examples of molecules?
- polymers
- resins
Vast repeating arrays of bonded elements
crystal (lattices)
Metallic and ionic bonds commonly form
crystal (lattices)
What is the repeated pattern in a crystal (lattice) called?
unit cell
What is the molecular weight of crystal (lattices)?
no molecular weight
What are two examples of crystal (lattices)?
- metal alloys
- ceramics
True or false: In crystal (lattices) there are fewer types of elements when compared to molecules.
True
Elements that donate their electrons towards formation of metallic bonds in repeating crystalline array
metals
Collections of metallic elements (Al) and nonmetallic elements (O) held together by ionic bonds in crystalline arrays
Ceramics
The most diverse class of material because their unit structure is the molecule rather than the crystal. Elements are generally bonded via covalent bonds.
Polymers
What are the 4 general properties of metals?
- strong, ductile
- high density
- high thermal/electrical conductivity
- opaque/optically reflective
What are the 4 general properties of ceramics?
- strong, brittle
- medium-high density
- poor thermal/electrical conductors
- opaque, translucent or transparent
What are the 4 general properties of polymers?
- weak, ductile
- low density
- low thermal/electrical conductivity
- opaque, translucent or transparent
What defines a materials properties?
the atoms and their bonding arrangement
What are the 4 material properties?
Ionic bonds….
A) electrons are shared in a cloud
B) electrons from one element is donated to another element
C) electrons from elements are shared to form a bond
D) only metallic elements are bonded
B) electrons from one element is donated to another element
A common characteristic/property of materials built with metallic bonds
A) only non-metallic elements are bonded
B) good conductors of electricity/heat
C) mechanically weak
D) polymers are built with metallic bonds
B) good conductors of electricity/heat
Strongest atomic bond
A) covalent
B) metallic
C) ionic
D) van der Waals
E) hydrogen
C) ionic
Weakest atomic bond
A) covalent
B) metallic
C) ionic
D) van der Waals
E) hydrogen
D) van der Waals
Ceramics are built with
A) ionic bonds
B) metallic bonds
C) covalent bonds
D) van der Waals
A) ionic bonds
Those properties that involve a reaction to an applied external load.
Mechanical properties
Why do mechanical properties involve a reaction to an applied external load?
To predict the behaviour and determine if the material can operate without failure
What are the 10 mechanical properties?
What is the force/load?
What is the definition of stress?
What are the units for load?
- Newton (N)
OR - Pounds (lbf)
Consider this example of a man and lady. Which heel is experiencing higher (A) load and (B) stress?
(A) male = higher load
- Fman = (100 kg)(9.81 m/s^2) = 981 N
- Flady = (50 kg)(9.81 m/s^2) = 490.5 N
(B) lady = higher stress
* if you took the above numbers and divided by the area, you would get the stress and the lady’s would be higher
What are the units for stress?
What are the two most common units used in the materials world?
- Megapascal (MPa)
- Gigapascal (GPa)
Describe the stresses in a tooth
What is the equation for strain?
change in length/ original length
How do you measure mechanical properties?
utilizing the stress-strain curve
https://www.youtube.com/watch?v=WSRqJdT2COE
Why are mechanical properties relevant?
- predict deformation after applying a load
- predict failure of material
- determine the range of usefulness of a material and establish the service life that can be expected
Which of the following is not considered a mechanical property?
A) stiffness
B) ductility
C) hardness
D) fatigue
E) hydrophobicity
E) hydrophobicity
What are the units for stress?
A) N/m^2
B) N/m^3
C) N/m
D) grams/cm
A) N/m^2
What are the units for strain?
A) cm/cm^2
B) %
C) cm
D) m
B) %
