APPLIED PHYSICS. 2 Text Books Book 1: Applied Physics by Dr. M. Chandra sekhar & Dr. Appala naidu, V.G.S. Book links Book 2 Introduction to Solid State. - презентация

1 APPLIED PHYSICS

2 2 Text Books Book 1: Applied Physics by Dr. M. Chandra sekhar & Dr. Appala naidu, V.G.S. Book links Book 2 Introduction to Solid State Physics by C. Kittel, Wiley Eastern Ltd. Book 3Nanotechnology by Mark Ratner and Daniel Ratner, Pearson Education

3 3 Suggested / Reference Books Book 1 Material science and Engineering by V Raghavan PHI publishers Book 2 Material Science by M Arumugam, Anuradha agencies Book 3Solid state physics by Ashcroft, Mermin, Thomson learning Book 4Solid state physics by Gupta & Kumar,K.Nath & Co.

4 4 Book 5: Applied Physics by P.K.Palaniswamy,Scitech Publications(India)Pvt.Ltd. Book 6: Material Science by MS Vijaya & G Rangarajan, Tata Mc Graw Hill Book 7: Applied Physics by K. Vijay Kumar & T.Srikanth, S. Chand & Company Ltd. Book 8: Nano materials by A.K. Bandyopadhyay, New Age International Publishers

5 5 UNIT-1 Bonding in solids Crystal structures X-ray diffractions

6 6 APPLIED PHYSICS CODE : 07A1BS05 CODE : 07A1BS05 I B.TECH I B.TECH CSE, IT, ECE & EEE CSE, IT, ECE & EEE UNIT-1: CHAPTER1 UNIT-1: CHAPTER1 NO. OF SLIDES :31 NO. OF SLIDES :31

7 7 S.No.ModuleLectureNo. PPT Slide No. 1IntroductionL18 2 Types of bonding L Estimation of cohesive energy. L Made lung constant. L431 UNIT INDEX UNIT-I

8 8 Introduction Introduction: Generally matter consists in three states i.e., depending on their internal structure. Normally the states are solid state, liquid state, and gaseous state. In solids stated as the closer collection of atoms result in bulk materials called solids. Solids are usually strong and exhibit elastic character. Solids can be broadly classified as either crystalline or Non-crystalline. The arrangement of atoms in a solids is determined by the character, strength and directionality of the binding forces. The bonds are made of attractive and repulsive forces. Lecture-1

9 9 Types of Bonding An atom consists of positively charged nucleus surrounded by negatively charged electron cloud. When two atoms are brought closer there will be both attractive and repulsive forces acting upon. The value of the energy need to move an atom completely away from its equilibrium position is a measure of Bonding Energy between them. This energy varies depending on the type of bonding. The bonds are made up of attractive and repulsive forces. Different charge distributions in the atoms give rise to different types of bonding. The bonds are made up of attractive and repulsive forces. Different charge distributions in the atoms give rise to different types of bonding. Lecture-2

10 10 Bonds generally classified into five classes. 1.Ionic bonding 2.Covalent bonding 3.Metallic bonding 4.Hydrogen bonding 5.Vander walls bonding.

11 11 Ionic Bonding: An ionic bonding is the attractive force existing between a positive ion and a negative ion when they are brought into close proximity. These ions are formed when the atoms of different elements involved lose or gain electrons in order to stabilize their outer shell electron configurations.

12 12 Properties of ionic solids: 1.Ionic solids are crystalline in nature. 2.They are hard and brittle. 3.They have high melting and boiling points. 4.Since all the electrons are tightly bound with the ions, ionic solids are good insulators of electricity.

13 13 5.They are soluble in polar solvents and insoluble in Non-polar solvents. 6.In an ionic crystal, a cation is surrounded by as many anions as possible and vice- versa. Examples of ionic solids: NaCl, KCl, KBr, MgO, MgCl 2,KOH, and Al 2 O 3 are few examples of ionic solids.

14 14 Covalent Bonding: The arrangement of electrons in an outer shell is achieved by a process of valence electron sharing rather than electron transfer. The arrangement of electrons in an outer shell is achieved by a process of valence electron sharing rather than electron transfer.

15 15 Properties of Covalent solids: 1.Covalent bonds are directional. Change in the direction of the bond results in the formation of different substance. 2.Since different covalent solids have very much different bond strengths, they exhibit varying physical properties. For example, the diamond is the hardest substance with very high melting point. It is a very good insulator of electricity. 3.Covalent solids are hard and brittle. They posses crystalline structure.

16 16 4.When compared with ionic solids, these solids have relatively low melting and boiling points. 5.Pure covalent solids are good insulators of electricity at low temperatures. 6.When covalent crystals are doped with certain impurities, they becomes semi-conductors. Examples of Covalent solids:S,I, Ge, Si, diamond and graphite.

17 17

18 18 Metallic Bonding: The valence electrons from all the atoms belonging to the crystal are free to move throughout the crystal. The crystal may be considered as an array of positive metal ions embedded in a cloud or sea of free electrons. This type of bonding is called metallic bonding.

19 19 Properties of Metallic solids: 1.Metallic bonds hold the atoms together in metals. 2.Metallic bonds are relatively weak. 3.Metallic solids are malleable and ductile. 4.Metallic bond is non directional.

20 20 5.They have high number of free electrons. 6.They possess high electrical and thermal conductivity. 7.Metals are opaque to light. Examples of metallic solids: Sodium, Copper, Gold, Silver, Aluminum.

21 21 Hydrogen Bonding: Covalently bonded atoms often produce an electric dipole configuration with hydrogen atom as the positive end of the dipole if bonds arise as a result of electrostatic attraction between atoms, it is known as hydrogen bonding.

22 22 Properties of Hydrogen solids: 1.The hydrogen bonds are directional. 2.The bonding is relatively strong as compared to other dipole-dipole interactions. 3.Hydrogen bonded solids have low melting points. 4.Since no valence electrons are available in such solids they are good insulators of electricity. 5.They are soluble in both polar and nonpolar solvents.

23 23 6.They are transparent to light. 7.Since elements of low atomic numbers form such solids, they have low densities. 8.When water is in the form of ice, hydrogen bond results in lower density; but when it melts, it becomes more closely packed liquid and hence its density increases. Example of hydrogen bonded solids: Water molecule in the form of ice, ammonia molecules.

24 24 Van der Waals(Molecular) Bonding: Weak and temporary (fluctuating) dipole bonds between hydrogen are known as van der Waals bonding and they are nondirectoinal. (OR) Weak and temporary (fluctuating) dipole bonds between hydrogen are known as van der Waals bonding and they are nondirectoinal. (OR) Secondary bonding arising from the fluctuating dipole nature of an atom with all occupied electron shell filled is called van der waals bonding. Secondary bonding arising from the fluctuating dipole nature of an atom with all occupied electron shell filled is called van der waals bonding.

25 25 Properties of Van der waals bonding: 1.Van der waals bonds are nondirectional. 2.Van der waals bonding is weaker than the hydrogen bonding. 3.Van der waals bonded solids have low melting point. 4.Since no valence electrons are available, such solids are good insulators of electricity.

26 26 5.They are soluble in both polar and non polar liquids. 6.They are usually transparent to light. Examples of Van der Waals bonded solids: Solid neon, Solid argon.

27 27 1.The mechanical, thermal, electrical and other properties of materials are related to chemical bonding and structure. 2.The atoms/molecules in solids are very strongly held together by interatomic/ intermolecular forces called bonding in solids.

28 28 3. The force that holds atoms together is called bonding force. Under the bonded condition the potential energy is minimum. 4.The amount of energy required to separate the atoms completely from the structure is called cohesive energy. This energy is also called energy of dissociation.

29 29 Primary Bondings have bond energies in the range of eV/bond. Ionic, Covalent and metallic bondings are the examples. Primary Bondings have bond energies in the range of eV/bond. Ionic, Covalent and metallic bondings are the examples. Secondary Bondings have energies in the range of eV/bond. Hydrogen bonding and van der waals bonding are the examples. Secondary Bondings have energies in the range of eV/bond. Hydrogen bonding and van der waals bonding are the examples.

30 30 Cohesive energy of NaCl molecule: Lecture-3

31 31 The Madelung constant is a function of crystal structure and can be calculated from the geometrical arrangement of ions in the crystal. The Madelung constant is a function of crystal structure and can be calculated from the geometrical arrangement of ions in the crystal. Lecture-4