Download to read offline
Intermolecular forces.pptx Intermolecular forces
- 1.
- 3.
- 4. OBJECTIVES After going throughthis module, you are expected to: 1. describe the types of intermolecular forces present in substances; 2. identify the types of intermolecular forces present between and among substances.
- 6. FORCES INTERMOLECULAR • Forces attract“between” two or more molecules. • Refer asVan der Waals forces and hydrogen bonds • Weak (in comparison of intra)
- 7. INTERMOLECULAR FORCES • Anattraction between two or more separate molecules. • The result of attractions between positively and negatively charged regions of separate molecules. • They are not as strong as intramolecular force (chemical bonds).
- 8. TYPES OF INTERMOLECULAR FORCES •Dipole-dipole interactions • Hydrogen bond • London force/Dispersion force • Ion Dipole
- 9. DIPOLE-DIPOLE INTERACTIONS • Attractionsbetween oppositely charged regions of a polar molecule. • Molecules that have permanent dipoles are attracted to each other. • The positive end of one is attracted to the negative end of the other and vice- versa. • These forces are only important when the molecules are close to each other.
- 10. • This existin polar substance • Polar substance - covalently bonded substances that contain partially positive and negative charges. • The more polar of the molecule, the higher its boiling points DIPOLE-DIPOLE INTERACTIONS
- 11. HYDROGEN BOND • Occurswhen Hydrogen is bonded to N, O, or F are unusually strong • It is a special type of dipole- dipole force • The result is a dipolar molecule • e.g H2O, NH3, HF
- 12. • Attraction dueto the constant motion of electrons. - it will temporary concentration of charge on one side of an atom/molecule • Exist between ALL molecules • Weakest IF LONDON DISPERSION FORCES
- 13. LONDON DISPERSION FORCES •It involve the attraction between temporarily induced dipoles • Example: • While the electrons in the 1s orbital of helium would repel each other (and, therefore, tend to stay far away from each other), it does happen that they occasionally wind up on the same side of the atom. It involve the attraction between temporarily induced dipoles
- 14. EXIST TO ALLELEMENTS
- 15. FACTORS AFFECTING LDF 1.Thestrength of dispersion forces tends to increase with increased molecular weight. -Larger atoms have larger electron clouds, which are easier to polarize.
- 16. 2. The shapeof the molecule affects the strength of dispersion forces: -long, skinny molecules (like n- pentane tend to have stronger dispersion forces than short, fat ones (like neopentane). -This is due to the increased surface area in n-pentane. FACTORS AFFECTING LDF
- 17. • Attractive forcethat results from the electrostatic attraction between an ion and a polar molecule that has a dipole. • Cations are attracted to the negative end of a dipole, while anions attracted to the positive end of a dipole. ION DIPOLE
- 18. ION DIPOLE • Afourth type of force, ion-dipole interactions are an important force in solutions of ions. • The strength of these forces are what make it possible for ionic substances to dissolve in polar solvents.
- 19.
- 20. MOLECULAR POLARITY Moleculewith a Positive and Negative Side (Polar) • Polar molecule (dipole) polar bonds are asymmetrically arranged Non Polar – no polar bonds or zero dipole moments
- 21. WHY IS POLARITYIMPORTANT? • Many Properties Depend on Polarity • Melting and Boiling Point • Surface Tension,Viscosity • Reactivity • Solubility (e.g., will it dissolve in water)
- 22. POLAR AND NONPOLAR • NON-polar covalent bonds -Bonds between identical atoms such as H- H, F-F involve equal sharing of e- • Polar covalent bonds -Bonds between different atoms involve unequal sharing of e- -Polar Covalent Bonds have a Partial Charge Separation
- 23. IN CONCLUSION • Polaritywill be important –In Determining Intermolecular Forces –Vapor Pressure, Boiling and Melting Points –SurfaceTension,Viscosity –Solubility –Reactivity (Organic Chemistry)
- 24.