Chapter 2 Bonding

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Introduction To Materials Science Chapter 2 Atomic Structure Interatomic Bonding. Atomic mass units Atomic weight ,The atomic mass unit amu is often used to express. atomic weight 1 amu is defined as 1 12 of the atomic mass. of the most common isotope of carbon atom that has 6. protons Z 6 and six neutrons N 6 ,Mproton Mneutron 1 66 x 10 24 g 1 amu . The atomic mass of the 12C atom is 12 amu , The atomic weight of an element weighted average of. the atomic masses of the atoms naturally occurring. isotopes Atomic weight of carbon is 12 011 amu , The atomic weight is often specified in mass per mole . A mole is the amount of matter that has a mass in grams. equal to the atomic mass in amu of the atoms A mole of. carbon has a mass of 12 grams , The number of atoms in a mole is called the Avogadro.
number Nav 6 023 1023 ,Nav 1 gram 1 amu ,Atomic weight of iron 55 85 amu atom 55 85 g mol. University of Tennessee Dept of Materials Science and Engineering 3. Introduction To Materials Science Chapter 2 Atomic Structure Interatomic Bonding. Some simple calculations, The number of atoms per cm3 n for material of density d. g cm3 and atomic mass M g mol , n Nav d M,Graphite carbon d 2 3 g cm3 M 12 g mol. n 6 1023 atoms mol 2 3 g cm3 12 g mol 11 5 1022,Diamond carbon d 3 5 g cm3 M 12 g mol. n 6 1023 atoms mol 3 5 g cm3 12 g mol 17 5 1022,Water H2O d 1 g cm3 M 18 g mol.
n 6 1023 molecules mol 1 g cm3 18 g mol 3 3 1022,molecules cm3. For material with n 6 1022 atoms cm3 we can calculate. mean distance between atoms L 1 n 1 3 0 25 nm , the scale of atomic structures in solids a fraction of 1 nm. or a few A , University of Tennessee Dept of Materials Science and Engineering 4. Introduction To Materials Science Chapter 2 Atomic Structure Interatomic Bonding. Electrons in Atoms I ,The electrons form a cloud,around the nucleus of radius. of 0 05 2 nm ,This Bohr picture looks,like a mini planetary system .
But quantum mechanics tells,us that this analogy is not. Electrons move not in circular orbits but in odd shaped. orbitals depending on their quantum numbers , Only certain orbits or shells of electron probability densities. are allowed The shells are identified by a principal. quantum number n which can be related to the size of the. shell n 1 is the smallest n 2 3 are larger The second. quantum number l defines subshells within each shell Two. more quantum numbers characterize states within the. subshells , University of Tennessee Dept of Materials Science and Engineering 5. Introduction To Materials Science Chapter 2 Atomic Structure Interatomic Bonding. Quantum Rules, n can take any positive integer value. l can take any integer value between, 0 and n 1 Therefore there are n.
possible values of l for a given n, ml can take any integer value. between l and l Thus there are, 2 l 1 values of ml for a given l. ms can take two values 1 2, Thus for any given value of l an. electron subshell there are 2 2 l 1 , electrons for any given value of n. an electron shell there are 2 2 l, 1 electrons add up all the.
subshells , University of Tennessee Dept of Materials Science and Engineering 6. Introduction To Materials Science Chapter 2 Atomic Structure Interatomic Bonding. Atomic Structure, Recall Isotopes,C12 where 12 6 Protons 6 Neutrons. C13 where 13 6 Protons 7 Neutrons Isotope ,Isotopic abundance of C13 1 1 . Carbon 12 01 g mol,Atoms having the same atomic number but varying. numbers of neutrons are isotopes,Mass of basic particles .
Particle Charge Mass amu 1 66x10 24 or 1 Nav ,Proton 1 1 00814 1 6734x10 24g . Neutron 0 1 00898 1 675x10 24g ,Electron 1 0 00055 0 000911x10 24g . The atomic mass unit amu is the basic unit of measurement. of an atom s mass one amu 1 12 12C6 1 amu 1 660420. x 10 24g , University of Tennessee Dept of Materials Science and Engineering 7. Introduction To Materials Science Chapter 2 Atomic Structure Interatomic Bonding. Electrons in Atoms II , The quantum numbers arise from solution of. Schrodinger s equation, Pauli Exclusion Principle only one electron can.
have a given set of the four quantum numbers , The Number of Available Electron States in Some. of the Electron Shells and Subshells, University of Tennessee Dept of Materials Science and Engineering 8. Introduction To Materials Science Chapter 2 Atomic Structure Interatomic Bonding. Electrons in Atoms III , 4s 4p 4d 4f, 5s 5p 5d 5f. Subshells by energy 1s 2s 2p 3s 3p 4s 3d 4s 4p 5s 4d 5p 6s 4f . Electrons that occupy the outermost filled shell the. valence electrons they are responsible for bonding . Electrons fill quantum levels in order of increasing. energy due to electron penetration ,Example Iron Z 26 1s22s22p63s23p63d64s2. University of Tennessee Dept of Materials Science and Engineering 9. Introduction To Materials Science Chapter 2 Atomic Structure Interatomic Bonding. University of Tennessee Dept of Materials Science and Engineering 10. Introduction To Materials Science Chapter 2 Atomic Structure Interatomic Bonding. Draft of the periodic table , Mendeleev 1869, University of Tennessee Dept of Materials Science and Engineering 11.
Introduction To Materials Science Chapter 2 Atomic Structure Interatomic Bonding. General Periodic Table Metals and Non Metals,Elements in the same column Elemental Group share. similar properties Group number indicates the number of. electrons available for bonding , 0 Inert gases He Ne Ar have filled subshells chem inactive. IA Alkali metals Li Na K have one electron in outermost. occupied s subshell eager to give up electron chem active. VIIA Halogens F Br Cl missing one electron in outermost. occupied p shell want to gain electron chem active. University of Tennessee Dept of Materials Science and Engineering 12. Introduction To Materials Science Chapter 2 Atomic Structure Interatomic Bonding. Periodic Table Electronegativity, The electronegativity values . Electronegativity a measure of how willing atoms are to. accept electrons,Subshells with one electron low electronegativity. Subshells with one missing electron high electronegativity. Electronegativity increases from left to right, Metals are electropositive they can give up their few.
valence electrons to become positively charged ions. University of Tennessee Dept of Materials Science and Engineering 13. Introduction To Materials Science Chapter 2 Atomic Structure Interatomic Bonding. Bonding Energies and Forces, Potential Energy E, attraction. equilibrium, This is typical potential well for two interacting atoms. The repulsion between atoms when they are brought close. to each other is related to the Pauli principle when the. electronic clouds surrounding the atoms starts to overlap . the energy of the system increases abruptly , The origin of the attractive part dominating at large. distances depends on the particular type of bonding . University of Tennessee Dept of Materials Science and Engineering 14. Introduction To Materials Science Chapter 2 Atomic Structure Interatomic Bonding. University of Tennessee Dept of Materials Science and Engineering 15. Introduction To Materials Science Chapter 2 Atomic Structure Interatomic Bonding. Bonding Behavior, But what does it mean , a High melting. temperature high elastic, modulus low thermal, expansion coefficient.
b Low melting,temperature low elastic,modulus high thermal. expansion coefficient, University of Tennessee Dept of Materials Science and Engineering 16. Introduction To Materials Science Chapter 2 Atomic Structure Interatomic Bonding. Relevant Equations, Coulombic Attraction Force Oppositely. Charged Ions, Fc K r2 r atomic separation distance between. ion centers, K k0 Z1q Z2q q 1 6 x 10 19 coulomb unit.
Z valence of the ion 1 2 3 1 2 3 , Fc k0 Z1q Z2q r2. Repulsive Force, FR e a p p are constants, At equilibrium FN 0 FA FR 0 FA . University of Tennessee Dept of Materials Science and Engineering 17. Introduction To Materials Science Chapter 2 Atomic Structure Interatomic Bonding. The electron volt eV energy unit convenient for, description of atomic bonding. Electron volt the energy lost gained by an electron. when it is taken through a potential difference of one. For q 1 6 x 10 19 Coulombs, V 1 volt, 1 eV 1 6 x 10 19 J. University of Tennessee Dept of Materials Science and Engineering 18. Introduction To Materials Science Chapter 2 Atomic Structure Interatomic Bonding. Types of Bonding,Primary bonding e are transferred or shared.
Strong 100 1000 KJ mol or 1 10 eV atom , Ionic Strong Coulomb interaction among negative. atoms have an extra electron each and positive atoms. lost an electron Example Na Cl , Covalent electrons are shared between the molecules . to saturate the valency Example H2, Metallic the atoms are ionized loosing some electrons. from the valence band Those electrons form a electron. sea which binds the charged nuclei in place,Secondary Bonding no e transferred or shared. Interaction of atomic molecular dipoles,Weak 100 KJ mol or 1 eV atom .
Fluctuating Induced Dipole inert gases H2 Cl2 , Permanent dipole bonds polar molecules H2O HCl . Polar molecule induced dipole bonds a polar molecule. like induce a dipole in a nearby nonpolar atom molecule . University of Tennessee Dept of Materials Science and Engineering 19. Introduction To Materials Science Chapter 2 Atomic Structure Interatomic Bonding. Ionic Bonding I ,Formation of ionic bond ,1 Mutual ionization occurs by electron transfer. remember electronegativity table , Ion charged atom. Anion negatively charged atom, Cation positively charged atom. 2 Ions are attracted by strong coulombic interaction. Oppositely charged atoms attract, An ionic bond is non directional ions may be attracted.
to one another in any direction,Example NaCl,11 Protons Na 17 Protons Cl. Electron Configuration Electron Configuration , Na metal Cl nonmetal . unstable unstable, Na cation Cl anion , stable Coulombic stable. Attraction, University of Tennessee Dept of Materials Science and Engineering 20. Introduction To Materials Science Chapter 2 Atomic Structure Interatomic Bonding. Ionic Bonding II ,Na Cl Na Cl , Electron transfer reduces the energy of the system of.
atoms that is electron transfer is energetically favorable. Note relative sizes of ions Na shrinks and Cl expands. Ionic bonds very strong nondirectional bonds, University of Tennessee Dept of Materials Science and Engineering 21. Introduction To Materials Science Chapter 2 Atomic Structure Interatomic Bonding. Predominant bonding in Ceramics, H He, 2 1 CaF2 , Li Be O F Ne. 1 0 1 5 CsCl 3 5 4 0 , Na Mg Cl Ar, 0 9 1 2 3 0 , K Ca Ti Cr Fe Ni Zn As Br Kr. 0 8 1 0 1 5 1 6 1 8 1 8 1 8 2 0 2 8 , Rb Sr I Xe, 0 8 1 0 2 5 . Cs Ba At Rn, 0 7 0 9 2 2 , 0 7 0 9,Give up electrons Acquire electrons.
Adapted from Fig 2 7 Callister 6e Fig 2 7 is adapted from Linus Pauling The. Nature of the Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition . Copyright 1960 by Cornell, University , University of Tennessee Dept of Materials Science and Engineering 22. Introduction To Materials Science Chapter 2 Atomic Structure Interatomic Bonding. Ionic Bonding III ,Crystal Structures in Ceramics. with predominantly ionic bonding,Crystal structure is defined by. Magnitude of the electrical charge on each ion Charge. balance dictates chemical formula Ca2 and F form, Relative sizes of the cations and anions Cations wants. maximum possible number of anion nearest neighbors. and vice versa , Stable ceramic crystal structures anions surrounding a.
cation are all in contact with that cation For a specific. coordination number there is a critical or minimum cation . anion radius ratio rC rA for which this contact can be. maintained , University of Tennessee Dept of Materials Science and Engineering 23. Introduction To Materials Science Chapter 2 Atomic Structure Interatomic Bonding. Covalent Bonding I , In covalent bonding electrons are shared between the. molecules to saturate the valency The simplest example is. the H2 molecule where the electrons spend more time in. between the nuclei than outside thus producing bonding . Formation of covalent bonds , Cooperative sharing of valence electrons. Can be described by orbital overlap, Covalent bonds are HIGHLY directional. Bonds in the direction of the greatest orbital overlap. Covalent bond model an atom can covalently bond with. at most 8 N N number of valence electrons,Example Cl2 molecule ZCl 17 1S2 2S2 2P6 3S2 3P5 .
N 7 8 N 1 can form only one covalent bond, University of Tennessee Dept of Materials Science and Engineering 24. Introduction To Materials Science Chapter 2 Atomic Structure Interatomic Bonding. Covalent Bonding II , Whereas the metallic and ionic CN is based on size. and hard sphere, Packing covalent bonding is based on a different set. Hard sphere model r R CN, ionic metallic 0 732 r R 1 8. r R 1 12, Covalent bond model 8 N N number of valence.
occupied p shell want to gain electron chem active General Periodic Table Metals and Non Metals 7 Introduction To Materials Science Chapter 2 Atomic Structure Interatomic Bonding University of Tennessee Dept of Materials Science and Engineering 13 Periodic Table Electronegativity Electronegativity a measure of how willing atoms are to accept electrons Subshells with one

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