Atomic bonding

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Atomic bonding

  1. 1. Interatomic forces present in atomic bonding can predict manyphysical properties of materials ( i.e. melting temperature, elasticity,thermal expansion, and strength).
  2. 2. For more help contact meMuhammad Umair Bukhari Engr.umair.bukhari@gmail.com www.bzuiam.webs.com 03136050151
  3. 3. Energy Fa Cation Anion Fr r As two ions approach each other, each atom exerts forces on theother. Magnitude of Forces is a function of interatomic distanceInteratomic Forces - Attractive Force, Fa - Repulsive Force, Fr
  4. 4. Bonding Energy, E0
  5. 5. Net Potential Energy between twoadjacent ions EN EA ER E Fdr r r EN F A dr F R dr
  6. 6. Bonding EnergyIn assessing the performance of materials, it’s important todraw attention to the relationship between materialproperties and structural elements.Finding the minimum of a Potential Energy Curvecorresponds to the energy released when two ions form abond, Bonding Energy.Bonding Energy and shape of Potential Energy Curve vs. Rvaries from material to material. Number of material properties depend on E0.
  7. 7. Co-efficient Of Thermal Expansion
  8. 8. Bonding is association of two atoms with in eachother. Interatomic bonding can be categorized as:◦ Primary bonding◦Secondary bonding
  9. 9. Primary BondingPrimary bonds are also knows as chemical bonds.Primary bonding necessarily involves the valence electronsfor its types.The nature of bonds depends up on the electronic structureof constituents atoms.Primary bonding arises from the tendency of atoms toassume the stable electronic structure like inert gases.
  10. 10. Types Of Primary Bonding▪Ionic bond▪Covalent bond▪Coordinate covalent bond▪Metallic bond
  11. 11. Ionic Bond»Ionic bond is due to electrostatic (columbic) forces of attractionbetween oppositely charged ions.» For two oppositely charged isolated ions, the attractive energy EAis a function of inter atomic distance. EA = A/r Where A = [1/4 €)] [Z1e x Z2 e] € =Permittivity of vacuum
  12. 12. Ionic Bond Cont……»Ionic bonds are formed where the difference in electro -negativities of the constituent’s atoms is considerable.» That̕ s reason ionic bonds are observed between the elementssituated at the horizontal extremities of the periodic table.»In ionic bonds, bond energies generally range between 600 and1500 kj/mole (3 and 8 eV/atom).»NaCl is example of ionic bond.
  13. 13. Covalent Bond» Covalent Bonds are formed by sharing of electrons betweenadjacent atoms.» Two atoms of covalent bonds will contribute at least one electroneach, to the bond and chaired pair of electrons may be consideredto belong to both of them.»Covalent bonds are favored between similar atomsi.e. non-metallic elemental molecules (H2,O2,Cl2 etc.)
  14. 14. Covalent Bond Cont….»Covalent bonds are also observed in molecules containingdissimilar atoms such as CH4, H2O, HNO3 etc.»Covalent bonds are found in diamond, silicon germanium andright hand side of periodic table such as GaAs,SiC etc.»The numbers of covalent bond that are possible for an atom aredetermined by valence electrons.
  15. 15. Covalent Bond Cont…» Covalent bonds may be very strong as in case of diamond (meltingpoint >3550 ºC).» Covalent bond may be very week in case of Bismuth (meltingpoint ~270 ºC).»It is found in polymers where basic molecular structure is a longchain of carbon atoms which are covalently bonded with two oftheir available 4 bonds per atom.»e.g. in CH4.
  16. 16. Co-ordinate Covalent Bond» A bond formed b/w two atoms when the shared pair of electrons is donated by one of the bonded atoms is called Co-ordinate Covalent Bond.» Atom which donates pair of electron called donor atom» Atom which accepts pair of electron called accepter atom» e.g. bonding b/w BF3 & NH3.
  17. 17. Metallic Bonding Metallic Bonding is found in metals and their alloys. Metallic atoms have one ,two or three valence electrons. These valence electrons are not bound to any particular atoms inmetals. They are more or less free to drift thought the entire metal.
  18. 18. Metallic Bonding Cont… These electrons belong to the metals as a whole forming a sea ofelectrons around different nuclei These nuclei also called ion cores having a net positive charge whichis equal in magnitude to the total valence electrons charge per atom. Free electrons act as a binder to hold the ion cores together. Metallic bond is non directional in nature and bonding energy inmetallic bond may be strong or weak. For example, bonding energy of mercury is 68 kj/mole and Tungstonhas a bonding energy 850 kj/mole.
  19. 19. Secondary Bonding Secondary bond also known as physical bonds. These are very weaker as compared to primary bonds. Bonding energy are of order of 10 kj/mole. It is more significant in noble gases which have stable electronstructures.
  20. 20. Secondary Bonding Cont…a) Fluctuating induced dipole bondsb) Polar molecule induced dipole bondc) Dipole dipole bond
  21. 21. Fluctuating Induced Dipole Bond Also known as London Dispersion Forces. An atom is normally electrically symmetric means over alldistribution of electrons is symmetric. As we know in constant vibration motion that can causeinstantaneous and short lived disturbance in electrical symmetry ♦for some atoms or molecules. Resulting in creation of dipole. Such dipole produces a displacement of electron distribution ofadjacent atoms or molecules which creates a dipole on second atom
  22. 22. Fluctuating Induced Dipole BondCont… Resulting weak attractive forces between the two, these forces aretemporary and short lived. These are the weakest bonds.
  23. 23. Polar Molecule Induced DipoleBond Some molecules, have separation between negatively andpositively charged regions due to asymmetrical arrangement. These molecules are termed as polar molecule. These permanent dipoles arise due to the difference in the electronegativities of the two atoms. Polar molecules may also induced dipoles in adjacent non-polarmolecule. So bond will formed as a result of attractive forces between thedipoles on two molecules.
  24. 24. Dipole Dipole bond Vander Waal forces will also exist between polar molecules. These forces called Dipole Dipole Bonds or Permanent DipoleBonds. The associated bonding energy are significantly greater than forbonds involving induced dipole. Hydrogen bonding is a special case of permanent dipole bond. Bonding energy incase of hydrogen bonding is 51 kj/mole.

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