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Lec 1-4.pdf Flashcards
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Lec 1-4.pdf Flashcards
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What did the Greek philosopher Democritus propose around 460 BC?
Democritus proposed that all matter was composed of invisible particles called 'atomos' meaning 'uncuttable', which is the origin of the name 'atoms'.
What is formed when two or more atoms come together?
Two or more atoms can form an electrically neutral entity called a molecule.
What results from the attraction between atoms and molecules?
Attraction between atoms and between molecules results in materials we can see and touch.
What is the basic unit of water?
The basic unit of water is a molecule made of two hydrogen atoms and one oxygen atom.
What happens when a molecule attains high kinetic energy?
If each molecule attains a kinetic energy that is higher than the attraction between these molecules, they appear in vapor form.
What is the transformation between vapor, liquid, and solid called?
The transformation between vapor, liquid, and solid is called the change of state.
What energy is required to change a solid to a liquid state?
A change from the solid to the liquid state will require additional energy, known as the latent heat of fusion.
What is the temperature at which a change from solid to liquid occurs known as?
The temperature at which this change occurs is known as the melting temperature or fusion temperature.
What is needed when water boils to transform the liquid to vapor?
When water boils, energy is needed to transform the liquid to vapor, and this quantity of energy is known as the heat of vaporization.
What process allows some solids to change directly to vapor?
Some solids can change directly to vapor by a process called sublimation, as seen in dry ice.
What are primary bonds dependent on?
The formation of primary bonds depends on the atomic structures and their tendency to assume a stable configuration.
What are primary bonds also called?
Primary bonds are also called chemical bonds.
What are the three different types of primary bonds?
The three different types of primary bonds are ionic, covalent, and metallic.
What is the classic example of ionic bonding?
The classic example of ionic bonding is the bond between Na and Cl of sodium chloride.
Where does ionic bonding exist in dentistry?
In dentistry, ionic bonding exists in some dental materials such as in gypsum.
What are covalent bonds?
In many chemical compounds, two valence electrons are shared by adjacent atoms, creating covalent bonds.
How are atoms held together in covalent bonding?
By virtue of sharing electrons, the two atoms are held together by covalent bonds to form a molecule that is sufficiently stable and electrically neutral.
Where does covalent bonding occur?
Covalent bonding occurs in many organic compounds such as in dental resins that form the backbones structure of hydrocarbon chains.
What characterizes metallic bonds?
The outer shell valence electrons can be removed easily from metallic atoms and form positive ions.
What is described as an electron cloud or gas in metals?
The free valence electrons can move about in the metallic space lattice to form what is sometimes described as an electron cloud or gas.
What properties do free electrons give metals?
The free electrons give the metal its characteristically high thermal and electrical conductivity.
What ability do metallic bonds provide to metals?
Metallic bonds are also responsible for the ability of metals to deform plastically.
What are secondary bonds?
Secondary bonds do not share electrons, instead charge variations among atomic groups of the molecule induce pole forces that attract adjacent molecules or parts of a large molecule.
What are Van der Waals forces?
Van der Waals forces of attraction arise from dipole attractions.
What is a hydrogen bond?
A hydrogen bond is a special case of dipole attraction of polar compounds.
What did Robert Hooke explain in 1665?
In 1665, Robert Hooke explained crystal shapes in terms of the packing of their component parts.
What is a crystal formation characterized by?
Crystals form a regularly spaced configuration known as a crystal lattice.
What is the simplest and most regular lattice?
The simplest and most regular lattice is cubic, characterized by axes that are all of equal length and meet at 90 degree angles.
What is a vacancy in a lattice structure?
Each missing atom site is called a vacancy.
What is a typical non-crystalline solid made of SiO2?
Glass is a typical non-crystalline solid of SiO2 because its atoms tend to be arranged in non-repeating units.
What are non-crystalline solids sometimes called?
Because this arrangement is also typical of liquids, non-crystalline solids are sometimes called supercooled liquids.
What are low internal energies?
Low internal energies are crystalline arrangements of the same atoms and molecules. They do not have a definite melting temperature but rather gradually soften as the temperature is raised.
What indicates the glass transition temperature (Tg)?
The temperature at which there is a abrupt increase in the thermal expansion coefficient, indicating increased molecular mobility, is called the glass transition temperature (Tg). It is characteristic of the particular glassy structure.
What do many dental materials consist of?
Many dental materials often consist of a non-crystalline glassy matrix and crystalline inclusions filler phase.
What is bond distance?
The bond distance is the interatomic distance at equilibrium that represents the distance between the centers of two adjacent atoms.
How is bonding energy defined?
Bonding energy is defined as the product of force and distance. Integration of the interatomic force over the interatomic distance yields the interatomic energy.
What happens to energy needs as atoms come closer together?
As the resultant force approaches zero, the energy needed to keep them apart decreases as the repulsion force becomes significant.
What is the condition of equilibrium in terms of energy?
The minimal energy corresponds to the condition of equilibrium and defines the equilibrium interatomic distance.
What happens to atomic or molecular vibration as temperature increases?
As the temperature increases, the amplitude of the atomic or molecular vibration increases, which also results in an increase in the mean interatomic distance and internal energy.
What is thermal expansion?
The overall effect of temperature increase leading to the increase in atomic or molecular vibration is known as thermal expansion.
What is the relationship between thermal expansion coefficient and melting temperature?
The linear coefficient of thermal expansion of materials with similar atomic or molecular structures tends to be inversely proportional to the melting temperature.
What is diffusion in solids?
Diffusion also occurs within solid materials but at a substantially slower rate.
What happens to atoms or molecules at any temperature above absolute zero?
At any temperature above absolute zero (273.15K), atoms or molecules of a solid possess different levels of kinetic energy, resulting in a distribution of atoms with various energy levels.
What is self-diffusion?
Self-diffusion occurs when atoms change position in pure single element solids even under equilibrium conditions.
What can cause diffusion in solids?
Diffusion can occur when there are vacancies of atoms within a solid formed during solidification or due to spacing in non-crystalline structures.
What is diffusion coefficient?
Diffusion coefficient is the amount of a substance that diffuses across a given unit area (e.g., 1 cm²) through a unit thickness (e.g., 1 cm) in one unit of time (e.g., 1 s).
What is adhesive bonding?
Adhesive bonding is a surface attachment process qualified by specifying the type of intermolecular attraction between the adhesive and the adherend.
What occurs during adhesion?
Adhesion occurs when molecules of one substrate are attracted to unlike different molecules of another substrate.
What is cohesion?
Cohesion occurs when molecules of one substrate are attracted to like same-kind molecules of another substrate.
What is a wetting agent?
A wetting agent, also known as a surfactant, is usually added in the impression material during the manufacturing process.
What factors affect wettability?
Impurities on the solid surface often yield a surface of lower energy than a clean surface and prevent any wetting by the adhesive.
What is the contact angle of wetting?
The contact angle defines the shape of the liquid, indicating the strength of adhesive versus cohesive forces at the interface.
What signifies complete wetting?
Complete wetting occurs at a contact angle of 0, while no wetting occurs at an angle of 180.
What is surface energy?
Surface energy is the energy that quantifies the work needed to disrupt intermolecular bonds resulting in a new surface.
What influences surface energy?
The functional chemical groups available or the type of crystal plane of a space lattice present at the surface may affect the surface energy.
What are the materials used in mechanical bonding?
Adhesive materials fill the voids or pores of solid surfaces and hold surfaces together by interlocking.
What is also referred to as micro mechanical bonding?
Mechanical bonding.
What happens when adhesive in the interfacial region is subjected to thermal changes and mechanical stresses?
Stress concentrations develop around the voids.
What may happen if the stress becomes too great in the adhesive bond?
It may initiate a separation in the adhesive bond adjacent to the void.
What can happen to cracks in the adhesive bond?
This crack may propagate from one void to the next, and the joint may separate under stress.
What is the process of separation in adhesive bonding often called?
Micro mechanical bonding.
Is the composition of tooth structure homogeneous?
No, the tooth composition is not homogeneous.
What types of components are present in tooth structure?
Both organic and inorganic components are present in different amounts in dentin as compared with enamel.
What occurs through certain components of the tooth?
There is a fluid exchange.
What must dental adhesive compete with for wetting the tooth surface?
Water.
What attempts are being made regarding dental adhesives?
Attempts are being made to use more hydrophilic resins that are not as sensitive to the presence of moisture as materials currently in use.
What is a potential issue with materials that adhere to organic compounds?
A material that can adhere to the organic compounds may not adhere to the inorganic components.
What is the adhesion characteristic of adhesives that bond to enamel in relation to dentin?
An adhesive that bonds to enamel may not adhere to dentin to the same extent.
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Explore key concepts on atomic structures, bonds, and materials with flashcards from Lec 1-4.pdf.
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