Forces Of Attraction


Published on

  • Be the first to comment

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

Forces Of Attraction

  1. 1. Forces of Attraction
  2. 2. Introduction <ul><li>Atoms aggregate to form molecules and lattice </li></ul><ul><li>Molecules aggregate to form condensed phases of matte </li></ul>
  3. 3. Aggregation of atoms, appositively charged ions and molecules is a consequence of <ul><li>Electrical forces exerted on the electrons of one particle by the nucleus (or nuclei) of the other </li></ul><ul><li> </li></ul>
  4. 4. Two broad categories of forces of attraction <ul><li>Intramolecular- forces that exist within molecules or fundamental/formula units </li></ul><ul><li>(forces that hold atoms or ions in a compound) </li></ul><ul><li>Intermolecular- forces of attraction that exist between the molecules in a compound </li></ul>
  5. 5. Intramolecular Forces <ul><li>Three types </li></ul><ul><li>Ionic </li></ul><ul><li>Covalent </li></ul><ul><li>metallic </li></ul>
  6. 6. Ionic or Electrovalent Bond <ul><li>Electrostatic force of attraction between ions of opposite charge </li></ul><ul><li>Ions are formed from atoms as a result of electron transfer from one atom to another </li></ul><ul><li>Formed as a result of a large difference in electronegativity of atoms </li></ul><ul><li>Formed between metals and non-metals </li></ul>
  7. 7. <ul><li>Electronegativity- the ability of an atom to attract (pull) electrons to itself. </li></ul><ul><li>Electrostatic force depends on the charge on the ions. </li></ul>
  8. 8. Properties <ul><li>Crystalline solids- rigidity and strength </li></ul><ul><li>High melting and boiling points </li></ul><ul><li>Conduct electricity in molten and aqueous state </li></ul><ul><li>They are hard </li></ul><ul><li>They are brittle </li></ul><ul><li>Soluble in polar solvents such as water (solute-solvent interactions) </li></ul>
  9. 9. Covalent Bonds <ul><li>Formed between atoms with a small difference in electronegativity </li></ul><ul><li>Formed by the overlapping of atomic orbital. </li></ul><ul><li>Molecular orbital result </li></ul><ul><li>Electrons are shared between nuclei of the two atoms </li></ul><ul><li>The attraction between the shared electrons and the nuclei that holds the molecule together </li></ul>
  10. 10. <ul><li>Two types of bonds are formed </li></ul><ul><li>Either sigma bonds </li></ul><ul><li>Or pi bonds </li></ul>
  11. 11. Sigma bonds <ul><li>Three possible ways for a sigma bond to be formed </li></ul><ul><li>Overlapping of two S-orbital </li></ul><ul><li>Overlapping of an S and a P-orbital </li></ul><ul><li>Head to head overlapping of two P-orbital </li></ul>
  12. 12. Pi bonds <ul><li>The side to side overlapping of two P orbital. </li></ul><ul><li>Electrons in this bond are delocalized </li></ul><ul><li>The electron density is above and below the plane of the sigma bond. </li></ul><ul><li>These bonds make a compound reactive </li></ul><ul><li>example in alkenes with the c-c double bond. </li></ul>
  13. 13. Properties of Covalent Compounds <ul><li>Liquids and gases at room temperature </li></ul><ul><li>Relatively low boiling point. </li></ul><ul><li>Do not conduct electricity </li></ul><ul><li>Insoluble in polar solvent </li></ul><ul><li>Soluble in non-polar solvent </li></ul>
  14. 14. Dative (Coordinate) covalent Bond <ul><li>One atom donates both electrons to form a covalent bond </li></ul><ul><li>Recall- in a normal covalent bond each atom donates an electron to be shared. </li></ul><ul><li>The atom donating the electrons must have at least one lone pair of the electrons. </li></ul>
  15. 15. <ul><li>The other atom must have an available empty orbital to accommodate this electron pair </li></ul><ul><li>example, boron trifluoride, aluminium trichloride. </li></ul><ul><li>can bond with say ammonia. </li></ul>
  16. 16. Metallic Bonds <ul><li>Positive ions surrounded by a sea of mobile (delocalized) electrons. </li></ul><ul><li>Strong electrostatic force of attraction binds the system together </li></ul><ul><li>Attraction between valence electrons and metal ion </li></ul>
  17. 17. What influences the strength of the bond? <ul><li>Availability of electrons </li></ul><ul><li>- More available delocalized electrons, the stronger the electrostatic attraction, the stronger the metallic bond. </li></ul>
  18. 18. <ul><li>Size of the charge on metal ion </li></ul><ul><li>Larger charge size, stronger the metallic bond. Explain. </li></ul><ul><li>example Al and Na </li></ul><ul><li>hard metal and soft metal </li></ul>
  19. 19. Properties of metals <ul><li>Hardness- Hardness refers to the ability of a metal to resist abrasion, penetration, cutting action, or permanent distortion </li></ul><ul><li>Brittleness- Brittleness is the property of a metal that allows little bending or deformation without shattering </li></ul>
  20. 20. <ul><li>Malleability- A metal that can be hammered, rolled, or pressed into various shapes without cracking or breaking or other detrimental effects is said to be malleable. </li></ul>
  21. 21. <ul><li>Ductility- Ductility is the property of a metal that permits it to be permanently drawn, bent, or twisted into various shapes without breaking </li></ul>
  22. 22. <ul><li>Elasticity- Elasticity is that property that enables a metal to return to its original shape when the force that causes the change of shape is removed. </li></ul><ul><li>Toughness </li></ul>
  23. 23. <ul><li>Density </li></ul><ul><li>Fusibility </li></ul><ul><li>Conductivity- Conductivity is the property that enables a metal to carry heat or electricity </li></ul><ul><li>Contraction </li></ul><ul><li>Expansion </li></ul>
  24. 24. Polar Covalent Bonds and Dipole Moments <ul><li>Polar bonds- formed between atoms of different electronegativity (EN) </li></ul><ul><li>- example, chlorine-carbon bond </li></ul><ul><li> * chlorine is more EN than carbon </li></ul><ul><li> * chlorine attracts the shared electron pair </li></ul><ul><li>to itself. </li></ul><ul><li> * C-Cl bond is polarized (delta negative </li></ul><ul><li> and delta positive </li></ul>
  25. 25. <ul><li>Polarized bonds have dipole moment. </li></ul><ul><li>Dipole- separation of charge within molecules </li></ul>
  26. 26. Intermolecular Forces
  27. 27. <ul><li>What are the forces between one chlorine molecule and another? </li></ul><ul><li>Intermolecular forces- forces between molecules or ions and influence their properties. </li></ul><ul><li>Molecular polarity gives rise to the forces of attraction between molecules </li></ul>
  28. 28. characteristics <ul><li>These forces are electrical – result from mutual attraction or mutual repulsion. </li></ul><ul><li>Generally very weak forces of attraction </li></ul><ul><li>Responsible for the states of matter </li></ul>
  29. 29. Characteristic Features <ul><li>Attractions exerted by one molecule of a molecular substance on another, such as the force of attraction between water molecules in ice. </li></ul>
  30. 30. <ul><li>Attractions between molecules of one substance and molecules of another, as when two liquids are mixed, or a molecular solid such as sugar is dissolved in a liquid. </li></ul>
  31. 31. <ul><li>Attractions between atoms of the noble gas elements, helium through radon. </li></ul><ul><li>Attraction between molecules of one substance and ions of another, as when an ionic compound dissolves in a liquid. </li></ul>
  32. 32. Types of I.M.F <ul><li>Ion-dipole </li></ul><ul><li>Dipole-dipole </li></ul><ul><li>London dispersion forces </li></ul><ul><li>Hydrogen bonds </li></ul>
  33. 33. Ion-Dipole Forces <ul><li>Result from electrical interactions between an ion and the partial charges on a polar molecule. </li></ul><ul><li>Dipolar molecule- a substance with both a positive and negative ends </li></ul>
  34. 34. <ul><li>In the presence of ions dipolar molecules orient themselves with positive end of dipole near the anion and negative end near cation </li></ul><ul><li>Magnitude of interaction depends on charge. </li></ul><ul><li>example: NaCl in water (ionic substance in dipolar water molecules). </li></ul>
  35. 35. <ul><li>Dipole-Dipole forces- Intermolecular forces that operate between neutral molecules having molecular dipole moments are called dipole-dipole forces </li></ul><ul><li>Result from interactions among dipoles on neighbouring molecules. </li></ul>
  36. 36. <ul><li>The more polar the substance the , the greater the strength of its dipole-dipole interactions. </li></ul><ul><li>The stronger the I.M.F that must be overcome for a substance to boil or melt. </li></ul>
  37. 37. Permanent Dipole
  38. 38. Inductive Forces and Dispersion <ul><li>Inductive forces arise from the distortion of the charge cloud induced by the presence of another molecule nearby. </li></ul><ul><li>Distortion arises from the electric field produced by the charge distribution of the nearby molecule. </li></ul>
  39. 39. <ul><li>These forces are always attractive but shorter ranged than electrostatic forces. </li></ul><ul><li>If a charged molecule (ion) induces a dipole moment in a nearby neutral molecule, the two molecules will stick together, even though the neutral molecule was initially round and uncharged </li></ul>
  40. 41. Dipole-Induced Dipole <ul><li>What would happen if HCl is mixed with argon, which has no dipole moment? </li></ul><ul><li>- The electrons on an argon atom are distributed homogeneously around the nucleus of the atom. </li></ul><ul><li>- Electrons are in constant motion. </li></ul>
  41. 42. <ul><li>Argon close to a polar HCl molecule, the electrons can shift to one side of the nucleus to produce a very small dipole moment that lasts for only an instant. </li></ul>
  42. 43. <ul><li>Distorting the distribution of electrons around the argon atom, the polar HCl molecule induces a small dipole moment on this atom. </li></ul><ul><li>A weak dipole-induced dipole force of attraction between the HCl molecule and the Ar atom is created </li></ul>
  43. 44. Dipole-Induced Dipole
  44. 45. Induced Dipole- Induced Dipole <ul><li>Some atoms are perfectly symmetrical. </li></ul><ul><li>No dipole exist </li></ul><ul><li>Some forces must exist </li></ul><ul><li>Atoms and Molecules such as; the noble gases, the halogens etc. </li></ul><ul><li>Electrons are in constant motion. </li></ul>
  45. 46. Example: Helium atom <ul><li>Movement of the electrons around the nuclei of a pair of neighboring helium atoms can become synchronized so that each atom simultaneously obtains an induced dipole moment. </li></ul>
  46. 47. <ul><li>There are fluctuations in electron density occurring constantly. </li></ul><ul><li>Creating an induced dipole-induced dipole force of attraction between pairs of atoms. </li></ul>
  47. 48. <ul><li>This force is relatively weak in helium. </li></ul><ul><li>Atoms or molecules become more polarizable as they become larger because there are more electrons to be polarized. </li></ul>
  48. 49. Induced Dipole- Induced Dipole
  49. 50. Hydrogen Bonding <ul><li>Hydrogen Bonding- a special kind of dipole-dipole force that occurs when a hydrogen atom is bonded to one of the very electronegative atoms, F, O, or N. </li></ul><ul><li>Electronegative atom must have at least a lone pair of electrons </li></ul>
  50. 51. Hydrogen Bonding <ul><li>Combination of forces </li></ul><ul><li>- normal covalent bond </li></ul><ul><li>- dipole-dipole interaction </li></ul>
  51. 52. Hydrogen Bonding <ul><li>The H-F, H-O, and H-N bonds are very polar, because the electronegative atom draws the bonding electron pair strongly to itself. This leaves the hydrogen nucleus exposed </li></ul>
  52. 54. Hydrogen Bonding in water
  53. 55. Summary I.M.F
  54. 56. Summary of Forces of Attraction
  55. 58. <ul><li> </li></ul>