Material Structure Flashcards
Performance of all dental materials depends on their ____\_ ____.
performance of all dental materials is based on their ATOMIC STRUCTURE.
The amount of energy necessary to tranform a liquid to a vapor is called the _____________.
LATENT HEAT OF VAPORIZATION
The _________ determines the state of a given substance.
KINETIC ENERGY.
if liquid has increase in kinetic energy it becomes a GAS.
if liquid has a decrease in kinetic energy it becomes a SOLID.
the energy released when a liquid becomes a solid is called the ________________.
Latent heat of fusion.
a liquid may vaporize under at any temperature between its freezing and boiling point as long as the air above it________________________.
As long as the air above it isn’t already saturated with vapor.
when a solid goes directly to its gas phase this process is called
SUBLIMATION
interatomic bonds can be classified as ____ or _____.
Primary or secondary.
Primary bonds are stronger than secondary bonds and can be of 3 different types:
1
2
3
1 Ionic
2 Covalent
3 Metallic
What is the difference between
ionic
covalent
metallic
ionic- electrons are TRANSFERRED between elements
Covalent- electrons are SHARED in precise orientations
Metallic- Electron sharing and formation of CLOUD of electrons that bonds elements together in lattice
Ionic bonds tend to be ______ and results in _____ structures
ionic bonds tend to be WEAKER and exist as CRYSTAL structures.
Covalent bonds share valence electrons.
A typical characteristic of covalent bonds is their_______ orientation.
Covalent bonds often have DIRECTIONAL ORIENTATION
Due to their unique metallic bond structure metals have excellent ______________ and have the ability to ___________
Due to their unique metallic bond structure metals have excellent electrical and thermal conductivity and have the ability to DEFORM PLASTICALLY
Secondary bonds are different than Primary bonds in that they DO NOT __________
Secondary bonds DO NOT SHARE ELECTRONS
Hydrogen bonding creates Asymmetrical/Symmetrical molecules that have a _____________.
Hydrogen bonding creates ASYMMERTRICAL molecules that have PERMANENT DIPOLES (molecule has directionality of charge)
What are Van der Walls forces?
Vander der walls forces result from temporary attraction of molecules due to attracting opposite polarities.
how is bond distance measured between two elements?
What limits the minimum distance this can be?
bond distance is measured from center to center of two atoms.
bond distance is limited by the diameter of the atoms involved.
what happens when two atoms get too close to one another?
they repel each other.
_________ position is where the forces of attraction and repulsion are equal and opposite in direction
Equilibrium Position
Recognize that there comes a point where if you decrease the distance between atoms they REPEL and can never be brought together.
As the distance increases the atoms will be ATTRACTED to one another but as the distance increases the force of attraction decreases.
Understand that there is a equilibrium position, if you try to decrease the distance when at equilibrium you get repulsion, if you increase the distance between them you get attraction.
When equilibrium position is reached the distance is a.
if the atom is moved either a repulsive or attractive force will result.
energy can be plotted as a function of displacement from equilibrium activity. This graph just shows that as you increase or decrease distance when two atoms are at equilibrium force results.
What is Thermal Energy?
Thermal energy is a measure of the atoms kinetic energy at a given temperature.
At any temperature above absolute zero atoms will vibrate, vibration increases with energy.
What causes thermal expansion?
thermal expansion is caused by the atoms vibrating with increasing amplitude which increases the space between the atoms and causes the substance to expand.
The energy curve is determined by the magnitude of attractive and repulsive forces.
The shallower the curve the less energy it takes to seperate the atoms, the deeper the curve the more energy it takes to seperate the atoms.
The deeper the curve the more energy required to reachmelting and boiling temperatures
How are stiffness and melting point related?
The stiffness of the material is proportional to the rate of change of the force.
Hence, a high melting point is usually accompanied by a greater stiffness.
How do free electrons affect conductivity of a material.
The number of free electrons in the material proportionately affects its thermal conductivity
Therefore, metals have high thermal conductivity; resins and ceramics have low thermal conductivity
what is the most common crystal lattice type of metals used in dentistry?
many of the metals used in dentistry belong to the cubic system.
atoms form parallel planes called CRYSTAL PLANES
What are the 3 common noncrystalline materials found in dentistry?
Waxes, Glass, Resin
Is glass a liquid or a solid?
Glass is considered a SUPERCOOLED LIQUID because of the arrangement of its crystals.
What is unique about the boiling point of Noncrystalline solids?
They dont have a set melting point, rather they become gradually softer as the temperature is raised.
What happens to atoms at absolute zero?
they stop vibrating
Absolute zero occurs at -273 celcius
What happens to diffusion as temperature or concentration increases?
As temperature or concentration increase the rate of diffusion also increases.
Some metals like mercury and gallium have very low melting points.
What does this allow them to do?
because these metals have such low melting points, they are able to diffuse into solid alloy particles as they set. LIKE IN AMALGAM
