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Forces Of Attraction
- 2. Introduction Atoms aggregate to form molecules and lattice Molecules aggregate to form condensed phases of matte
- 3. Aggregation of atoms, appositively charged ions and molecules is a consequence of Electrical forces exerted on the electrons of one particle by the nucleus (or nuclei) of the other www.wpi.edu/academics/Depts/chemistry/course/general/concept6.html.
- 4. Two broad categories of forces of attraction Intramolecular- forces that exist within molecules or fundamental/formula units (forces that hold atoms or ions in a compound) Intermolecular- forces of attraction that exist between the molecules in a compound
- 5. Intramolecular Forces Three types Ionic Covalent metallic
- 6. Ionic or Electrovalent Bond Electrostatic force of attraction between ions of opposite charge Ions are formed from atoms as a result of electron transfer from one atom to another Formed as a result of a large difference in electronegativity of atoms Formed between metals and non-metals
- 7. Electronegativity- the ability of an atom to attract (pull) electrons to itself. Electrostatic force depends on the charge on the ions.
- 8. Properties Crystalline solids- rigidity and strength High melting and boiling points Conduct electricity in molten and aqueous state They are hard They are brittle Soluble in polar solvents such as water (solute-solvent interactions)
- 9. Covalent Bonds Formed between atoms with a small difference in electronegativity Formed by the overlapping of atomic orbital. Molecular orbital result Electrons are shared between nuclei of the two atoms The attraction between the shared electrons and the nuclei that holds the molecule together
- 10. Two types of bonds are formed Either sigma bonds Or pi bonds
- 11. Sigma bonds Three possible ways for a sigma bond to be formed Overlapping of two S-orbital Overlapping of an S and a P-orbital Head to head overlapping of two P-orbital
- 12. Pi bonds The side to side overlapping of two P orbital. Electrons in this bond are delocalized The electron density is above and below the plane of the sigma bond. These bonds make a compound reactive example in alkenes with the c-c double bond.
- 13. Properties of Covalent Compounds Liquids and gases at room temperature Relatively low boiling point. Do not conduct electricity Insoluble in polar solvent Soluble in non-polar solvent
- 14. Dative (Coordinate) covalent Bond One atom donates both electrons to form a covalent bond Recall- in a normal covalent bond each atom donates an electron to be shared. The atom donating the electrons must have at least one lone pair of the electrons.
- 15. The other atom must have an available empty orbital to accommodate this electron pair example, boron trifluoride, aluminium trichloride. can bond with say ammonia.
- 16. Metallic Bonds Positive ions surrounded by a sea of mobile (delocalized) electrons. Strong electrostatic force of attraction binds the system together Attraction between valence electrons and metal ion
- 17. What influences the strength of the bond? Availability of electrons - More available delocalized electrons, the stronger the electrostatic attraction, the stronger the metallic bond.
- 18. Size of the charge on metal ion Larger charge size, stronger the metallic bond. Explain. example Al and Na hard metal and soft metal
- 19. Properties of metals Hardness- Hardness refers to the ability of a metal to resist abrasion, penetration, cutting action, or permanent distortion Brittleness- Brittleness is the property of a metal that allows little bending or deformation without shattering
- 20. 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.
- 21. Ductility- Ductility is the property of a metal that permits it to be permanently drawn, bent, or twisted into various shapes without breaking
- 22. 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. Toughness
- 23. Density Fusibility Conductivity- Conductivity is the property that enables a metal to carry heat or electricity Contraction Expansion
- 24. Polar Covalent Bonds and Dipole Moments Polar bonds- formed between atoms of different electronegativity (EN) - example, chlorine-carbon bond * chlorine is more EN than carbon * chlorine attracts the shared electron pair to itself. * C-Cl bond is polarized (delta negative and delta positive
- 25. Polarized bonds have dipole moment. Dipole- separation of charge within molecules
- 27. What are the forces between one chlorine molecule and another? Intermolecular forces- forces between molecules or ions and influence their properties. Molecular polarity gives rise to the forces of attraction between molecules
- 28. characteristics These forces are electrical – result from mutual attraction or mutual repulsion. Generally very weak forces of attraction Responsible for the states of matter
- 29. Characteristic Features Attractions exerted by one molecule of a molecular substance on another, such as the force of attraction between water molecules in ice.
- 30. 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.
- 31. Attractions between atoms of the noble gas elements, helium through radon. Attraction between molecules of one substance and ions of another, as when an ionic compound dissolves in a liquid.
- 32. Types of I.M.F Ion-dipole Dipole-dipole London dispersion forces Hydrogen bonds
- 33. Ion-Dipole Forces Result from electrical interactions between an ion and the partial charges on a polar molecule. Dipolar molecule- a substance with both a positive and negative ends
- 34. In the presence of ions dipolar molecules orient themselves with positive end of dipole near the anion and negative end near cation Magnitude of interaction depends on charge. example: NaCl in water (ionic substance in dipolar water molecules).
- 35. Dipole-Dipole forces- Intermolecular forces that operate between neutral molecules having molecular dipole moments are called dipole-dipole forces Result from interactions among dipoles on neighbouring molecules.
- 36. The more polar the substance the , the greater the strength of its dipole-dipole interactions. The stronger the I.M.F that must be overcome for a substance to boil or melt.
- 37. Permanent Dipole
- 38. Inductive Forces and Dispersion Inductive forces arise from the distortion of the charge cloud induced by the presence of another molecule nearby. Distortion arises from the electric field produced by the charge distribution of the nearby molecule.
- 39. These forces are always attractive but shorter ranged than electrostatic forces. 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
- 41. Dipole-Induced Dipole What would happen if HCl is mixed with argon, which has no dipole moment? - The electrons on an argon atom are distributed homogeneously around the nucleus of the atom. - Electrons are in constant motion.
- 42. 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.
- 43. Distorting the distribution of electrons around the argon atom, the polar HCl molecule induces a small dipole moment on this atom. A weak dipole-induced dipole force of attraction between the HCl molecule and the Ar atom is created
- 45. Induced Dipole- Induced Dipole Some atoms are perfectly symmetrical. No dipole exist Some forces must exist Atoms and Molecules such as; the noble gases, the halogens etc. Electrons are in constant motion.
- 46. Example: Helium atom 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.
- 47. There are fluctuations in electron density occurring constantly. Creating an induced dipole-induced dipole force of attraction between pairs of atoms.
- 48. This force is relatively weak in helium. Atoms or molecules become more polarizable as they become larger because there are more electrons to be polarized.
- 49. Induced Dipole- Induced Dipole
- 50. Hydrogen Bonding 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. Electronegative atom must have at least a lone pair of electrons
- 51. Hydrogen Bonding Combination of forces - normal covalent bond - dipole-dipole interaction
- 52. Hydrogen Bonding 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
- 54. Hydrogen Bonding in water
- 55. Summary I.M.F
- 56. Summary of Forces of Attraction