Chapter 2 Flashcards
What is electronegativity?
The tendency of an atom to attract an electron to its outer shell.
What is a primary bond?
The movement of electrons to form a stable electronic configuration
What are the material properties of materials that are ionically bonded?
> High strength
High elastic modulus
High melting point
Poor electrical conductivity
What are the material properties of materials that are covalently bonded?
> Very high elastic modulus
High inherent strength
High melting point
Low electrical conductivity
What are the material properties of materials that are metallically bonded?
> More forgiving to deformation > Highly electrically conductive > High thermal conductivity > Malleable > Low melting point
What is a ceramic (As in what is the material made from)?
Ceramics are made from a metal and a non-metal
What bonds form within a ceramic material?
Ionic and covalent bonds mixed together
What are the material properties of materials that are ceramic?
> Thermal and electrically insulative
> They are brittle
What is an issue with ceramic manufacturing?
Flaws in the microstructure of the ceramic can be hard to control and affect material strength
Talk about plastic deformation with regards to ceramics
There is very little plastic deformation before fracture making it brittle
What are intramolecular forces?
Forces are between electrons and nuclei
What are intermolecular forces?
Intermolecular forces are between molecules
A bond equilibrium is reached between two atoms bonded together. Talk about this. 5 points.
> There is the attraction between the oppositely charged nuclei and electrons and the repulsion of the similarly charged nuclei. This affects the bond length
An equilibrium is reached and at this point the energy is lowest.
The equilibrium position is equal to the sum of the atomic radii
The internuclear separation that corresponds to the energy minimum is called the bond length
The energy required to separate the atoms to an infinite distance is the bond strength (energy)
Name all the aspects of a force distance graph for atomic bonding
> Y-axis = Force
X-axis = Distance
Positive force is repulsive
Negative force is attractive
r0 is the position where the forces balance and is equal to the average length of the bond.
r > 10 × r0 = Little/no force between atoms
r < 10 × r0 = Attractive force increases
r < r0 = repulsive force dominates
Area under graph is potential energy
How can the phase of material be determined?
> Using the graph of potential energy
> Determined by the balance between thermal kinetic energy (Et) and binding energy (εb)
Where do solid materials lie on the potential energy graph? why?
Around the position of r0
> Bonding energy is high so the shape and volume is approximately constant
Where do liquids lie on the potential energy graph?
Around 5 × r0
> Bonding energy is weak so the shape is varied
> Volume is approximately constant
> Molecules vibrate and are not fixed in place
Where do gasses lie on the graph of potential energy?
Anywhere, where repulsive force dominates.
> Variable shape and volume
> Occupies all space available
> Molecules are not restrained, random motion
What is the symbol for thermal kinetic energy and binding energy?
Thermal kinetic energy = Et
Binding energy = εb
What are the equations for thermal and binding energy for each state?
Solid: Et < εb/10
Liquid: εb/10 < Et < εb
Gas: Et > εb
What is a secondary bond?
Attractions between molecules due to uneven charge distribution between molecules
What is an electric dipole?
This is the attraction between two molecules because of an uneven distribution of charge between molecules
What is a van der waals bond?
It is a hydrogen bond and is due to the position of the electrons around an nucleus of an atom in a molecule
Talk about secondary bonds with regards to polymers
Polymers melt easily because they have few and weak secondary bonds. The bonds are easily broken. This also gives it the ability to have a low elastic modulus.
What is the equation for hookes law?
F = kx
What is the equation for hookes law with regards to bonds in a molecule?
F = S0(r-r0)
What is the equation for stress?
σ = F/A
What is the equation for stress with regards to bonds in a molecule?
σ = S0(r-r0)/r0^2
What is the equation for strain?
ε = (x-x0)/x0
What is the equation for strain with regards to the bonds in a molecule?
ε = (r - r0)/r0
What is the equation for youngs modulus?
E = σ/ε
What is the equation for youngs modulus with regards to a molecule?
E = S0/r0
What are the properties of a polymer? Why?
> low melt temperature and bonding energy
bonds readily broken and reformed by thermal energy and stress
low elastic modulus.
> This is because of ID-ID dipoles between molecules
