STRUCTURE OF MATTER &PRINCIPLES OF ADHESION

THIS TOPIC INCLUDE ALL ABOUT STRUCTURAL PROPERTIES OF MATTER AND HOW THEY GET ADHERED TO EACH MOLECULE.

1. STRUCTURE OF MATTER & PRINCIPLES OF ADHESION PRESENTED BY ASTHA PALIWAL JR 1

2. INTRODUCTION 2 : The Greek philosopher Democritus proposed that all matter was composed of indivisible particles called atomos . : An atom consists of nucleus surrounded by a cloud of negatively charged electrons. Except for the hydrogen atom , where there are no neutrons, the nucleus contains a mix of positively charged protons & electrically neutral neutrons. : Atom becomes a negative ion when it gains electrons or a positive ion when it loses electrons. : Two or more atoms can form an electrically neutral entity called a molecule.

3. Change of State : Transformation between vapor, liquid & solid is called change of state . : Change from solid to liquid state will require energy called kinetic energy to break loose from the force of attraction. This additional energy is called LATENT HEAT OF FUSION. : Temperature at which this change occurs k/a melting / fusing temperature. Some solid change directly to process k/a sublimation. :When water boils energy needed to transform the liquid to vapor , this quantity of energy is known as Heat of Vaporization . 3

4. INTERATOMIC BONDS : The forces that holds atom together are called cohesive forces. : The electronic structure of an atom is relatively if it has eight electrons in its outer valence shell, as noble gases do , except for helium , which has only 2 electrons . : Interatomic bonds may be classified as primary or secondary . Presentation title 4

5. INTERATOMIC BONDS : PRIMARY BONDS – A bond that forms between atoms & that involves the exchanging or sharing of electron. Its formation depends on the atomic structures & their tendency to assume a stable configuration. : SECONDARY BONDS – A bond that involves attraction between molecules. In contrast with primary bonds , secondary bonds do not share electrons. Instead charge variations among atomic groups of the molecule induce dipole forces that attract adjacent molecules or a part of large molecule . Presentation title 5

6. Classification of Interatomic Bonds Presentation title 6 PRIMARY BONDS IONIC COVALENT METALLIC VAN DER WAALS FORCE HYDROGEN BONDS SECONDARY BONDS ATOMIC BONDS

7. Primary Interatomic Bonds Presentation title 7 1) IONIC BOND - Ionic bonds results from the mutual attraction of positive & negative charges . : The classic example is sodium chloride . :In Na + and Cl – of sodium chloride , sodium atom contains one valence electron in its outer shell & the chlorine atom has seven electrons in its outer shell , the transfer of sodium valence electrons to the chlorine atom results in stable compound Na + Cl - :In dentistry , ionic bonding are present in some dental materials , such as GYPSUM STRUCTURES & PHOSPHATE –BASED Cements.

8. IONIC BONDS Presentation title 8

9. COVALENT BONDS Presentation title 9 : In many chemical compounds , two valence electrons are shared by adjacent atoms . By virtue of sharing electrons , the two atoms are held together by covalent bonds to form a molecule that is sufficiently stable , & electrically neutral in a definite arrangement. :The hydrogen gas molecule , H2 , exemplifies covalent bonding. :Covalent bonding occurs in many organic compounds , such as in DENTAL RESINS .

10. COVALENT BONDS Presentation title 10

11. METALLIC BONDS Presentation title 11 : The outer shell valence electrons can be removed easily from metallic atoms and form positive ions . : The free valence electrons can move about in the metal space lattice to form which is sometimes describes as an electron cloud or gas. : The electrostatic attraction between the electron cloud and the positive ions in the lattice provides the force that bond metal atom together as a solid. : Free electrons gives the metal its characteristically HIGH THERMAL & ELECTRICAL CONDUCTIVITY .

12. D IAGRAM : metallic bond characterized by electron sharing& formation of a cloud of electrons that bond to positively charged nucleus Presentation title 12

13. SECONDARY BONDS Presentation title 13 VAN DER WAALS FORCES : : These Van Der Waals forces of attraction arise from dipole attractions . : In the case of polar molecules , dipoles ate induced by an unequal sharing of electrons.

14. Van Der Waals Forces Presentation title 14

15. Van Der Waals Forces Presentation title 15

16. HYDROGEN BOND Presentation title 16 :The hydrogen bond is a special case of dipole attraction of polar compounds . : It can be understood by water molecule . Attached to the oxygen atoms are two hydrogen atoms. : These bonds are COVALENT .

17. Diagram : Hydrogen bond formation between water molecules . The polar water molecules bonds to adjacent water molecule Presentation title 17

18. HYDROGEN BONDS Presentation title 18 : The protons of the hydrogen atoms pointing away from the oxygen atoms are not shielded efficiently by the electrons . They become positively charged . : On the opposite side of the water molecules , the electrons that fill the outer shell of the oxygen provides a negative charge . The positive hydrogen nucleus is attracted to the unshared electrons of neighboring water molecules .

19. ATOMIC ARRANGEMENT Presentation title 19 : All materials we use consist of trillions of atoms . : In 1665 , Robert Hooke explained crystal shapes in terms of packing of their component parts , like stacking musket balls in piles . : In the solid state , atoms combine in a manner that ensures minimal internal energy . for example : sodium & chlorine share one electron at the atomic scale . In the solid state , like grains of salt , they do not exist in individual pairs ; infact each sodium ion is attracted to six chlorine ions & vice versa .

20. ATOMIC ARRANGEMENT Presentation title 20 : A space lattice can be defined as any arrangement of atoms in space in which every atom is situated similarly to every other atom. : These are structures where regularly spaced configurations do not occur in the solid state.

21. CRYSTALLINE STRUCTURE Presentation title 21 : The type of space lattice is defined by the length of each of three unit cell edges & the angles between the edges. : The simplest & more regular lattice is a cubic lattice.

22. CRYSTALLINE STRUCTURE Presentation title 22 : It is characterized by axes that are all of equal length & meet at 90-degrees angles , representing the smallest repetitive volume of crystal , which is called unit cell .

23. BODY CENTERED CUBIC Presentation title 23 : In the body centered cubic array , all angles are 90 degree & all are equidistant from one another in horizontal & vertical direction. Metal atoms are located at corners of the unit cell & one atom is at the center of unit cell. :Iron at room temperature has an atom at each corner of the cube & another atom at the body center of the cube. This crystal form is called known as BODY – CENTERED CUBIC cell .

24. BODY CENTERED CUBIC Presentation title 24

25. FACE CENTERED CUBIC Presentation title 25 : This array has 90 - degree angle & atomic centers that are equidistant horizontally & vertically , but atoms are located in the centers of faces with no atom in the center of the unit cell. :Copper on the other hand ,has additional atoms at center of each face of unit cell but none at the center of the cube . This form is called as FACE CENTERED CUBIC cell .

26. FACE CENTERED CUBIC Presentation title 26

27. CRYSTALLINE BONDS Presentation title 27 : All metallic – based dental materials are crystalline . Some pure ceramics , such as alumina and zirconia core materials , are entirely crystalline. : Crystalline inclusions provide desired properties including color, opacity , increased thermal expansion coefficients & in some dental ceramics increased radiopacity .

28. CRYSTALLINE SiO2 ( QUARTZ) Presentation title 28

29. NONCRYSTALLINE BONDS Presentation title 29 : Glass is a typical noncrystalline solid of SiO2 because its atoms tend to be arranged in non repeating units . : The ordered arrangement of the glass is more or less locally interspersed with a considerable number of disordered units. Because this arrangement is also typical of liquids , such solid are sometimes called SUPERCOOLED LIQUIDS .

30. AMORPHOUS SiO2 ( GLASS) Presentation title 30

31. NONCRYSTALLINE BONDS Presentation title 31 Because of the complexity of physical configuration of polymer chains , the molecules of resins are not favored to arrange in orderly repeating patterns . Therefore, Polymeric – Based materials used in dentistry are usually non- crystalline .

32. GLASS TRANSITION TEMPERATURE Presentation title 32 : The temperature at which there is an abrupt increase in the THERMAL EXPANSION COEFFICIENT , indicating increased molecular mobility , is called the GLASS TRANSITION TEMPERATURE. Many dental materials often consists of a non crystalline glassy matrix & crystalline inclusions .

33. Interatomic Bond Distance & Thermal Energy Presentation title 33 : Between any two atoms , there are forces of attraction drawing them together & forces of repulsion pushing them apart . Both force increases as the distance between the atoms decreases . : The force of repulsion increases much more than the force of attraction as the atoms gets closer.

34. BOND DISTANCE Presentation title 34 :The position at which both forces are equal in magnitude ( but opposite in direction ) is considered the equilibrium position of atoms . : The interatomic distance at equilibrium represents the distance between the centers of the two adjacent atoms.

35. DIAGRAM :RELATIONS OF INTERATOMIC FORCES TO INTERATOMIC DISTANCE Presentation title 35

36. BONDING ENERGY Presentation title 36 : Energy is defined as the product of force & distance . :Integration of the interatomic distance yields interatomic energy . :In contrast with the resultant forces , energy needed to keep them far apart does not change much initially as two atoms comes closer together. As the resultant forces approaches zero , the energy needed to keep them apart decreases as the repulsion forces becomes significant . The energy finally reaches a minimum when the resultant forces becomes zero.

37. BONDING ENERGY Presentation title 37 Thereafter , the energy increases rapidly because the resultant repulsive forces increases rapidly with little change in interatomic distance . :The minimal energy corresponds to the condition of equilibrium & defines the equilibrium interatomic distance.

38. THERMAL ENERGY Presentation title 38 :The atoms in a crystal at temperature above absolute zero are in a constant state of vibration , & the average amplitude is dependent on the temperature . Higher the temperature , the greater the amplitude & consequently the greater the kinetic energy .

39. THERMAL ENERGY Presentation title 39 :As the temperature increases , the amplitude of the atomic vibration increases . It also follows that the mean interatomic distance increases as well as the internal energy . The overall effect is the phenomenon known as THERMAL EXPANSION .

40. THERMAL ENERGY Presentation title 40 :As the temperature increases from T0 to T5 , the mean interatomic distance increase is less with the deeper energy trough than that in shallower energy trough . This means that the linear coefficient of thermal expansion of materials with similar atomic or molecular structures tend to be inversely proportional to the melting temperature . : If the temperature continues to increase , the increase of interatomic distance will result in change of state .

41. Presentation title 41

42. THERMAL ENERGY Presentation title 42 :A solid melts to liquid , & liquid subsequently vaporizes to a gas . For a solid with greater minimum energy i.e. a deeper trough depth , greater amounts of energy are required to achieve melting & boiling , which corresponds to higher melting & boiling temperature.

43. : Less thermal expansion and a higher melting temperature are expected. Presentation title 43

44. THERMAL ENERGY Presentation title 44 : The net force on the atoms at equilibrium distance is zero , but small displacements results in rapidly increasing forces to maintain equilibrium distance. : The stiffness or elastic modulus of the material is proportional to the rate of change of the force with a change in displacement that is measured by the slope of the net force curve near equilibrium . A greater the slope of force curve implies a narrower , deeper trough in the energy curve.

45. DIFFUSION Presentation title 45 : When we place a drop of ink in a bowl of water , we observe the spread of the ink in the water. It will eventually disperse through the entire body of the water . This process is called diffusion. The same process also occurs within solid materials but a substantially slower rate .

46. Presentation title 46 : There is a distribution of atoms with a particular energy that varies from very low to high , with the average energy at equilibrium . If the energy of a particular atom exceeds the bonding energy , it can move to another position in the lattice.

47. SELF -DIFFUSION Presentation title 47 : Atoms change position in pure , single element solids even under equilibrium conditions ; this process is also known as self diffusion . As with any diffusion process , the atoms or molecules diffuse in solid state in an attempt to reach an equilibrium state . : Diffusion may also occur in the other direction to produce a concentration of atoms in a solid . Like in a solid copper –silver alloy with higher copper concentration may cause supersaturation of copper in silver , which forces diffusion of copper atoms to increase the concentration of copper locally , causing them to precipitate.

48. DIFFUSION Presentation title 48 : Diffusion rates increases with temperature , the chemical potential gradient , concentration gradient or lattice imperfections increases . : Diffusion rate will decrease with an increase in atom size & interatomic bonding. : The diffusion constant that is uniquely characteristic of the given element in a compound , crystal or alloy is known as DIFFUSION COEFFICIENT . The diffusion coefficients of elements in most crystalline solids at room temperature are very low .