Covalent Compounds

1. Covalent Compounds

2. Covalent Compounds • Usually soft and squishy • Not soluble in water • Does not conduct electricity • Low melting points • Low boiling points

3. Two Types of Bonds • Ionic: Electrons are transferred • Covalent: Electrons are shared • Non-polar covalent: equally shared • Polar Covalent: unevenly shared

4. Naming Covalent Compounds

5. NAMING COMPOUNDS Nonmetal – Nonmetal USE PREFIXES! • Change the ending of the second word to -ide • No mono on the first word • Drop any double vowels

6. Covalent Prefixes

7. THE PREFIX TELLS YOU HOW MANY ATOMS YOU HAVE!NO CRISS CROSS!!!!

8. Examples Carbon Monoxide Carbon Dioxide Sulfur Dioxide Sulfur Trioxide DinitrogenTetrahydride DinitrogenTrioxide • CO • CO2 • SO2 • SO3 • N2H4 • N2O3

9. Examples Si2F6 C2Cl8 PBr5 NO SeF2 H2O • disilicon hexafluoride • tricarbonoctachloride • phosphorus pentabromide • nitrogen monoxide • selenium difluoride • dihydrogen monoxide

10. EMPIRICAL AND MOLECULAR FORMULAS

11. Define Empirical Formula: • A chemical formula that gives the simplest whole-number ratio of the elements in the formula. Which of the following is an empirical formula? CO2 C2O4 Fe2Cl6 FeCl3

12. Define Molecular Formula: A chemical formula that gives the actual number of the elements in the molecular compound. For the following molecular formulas, write the empirical formula: Molecular: Empirical: C2H4 C6H12O6 C9H21O6N3

13. Lewis Structures

14. Lewis Structures for Compounds • The pair of dots between two symbols represents the shared pair. • How many shared pairs does each fluorine have below? • An unshared pair, also called a lone pair, is a pair of electrons that is not involved in bonding and that belongs exclusively to one atom.

15. Lewis Structures • The shared pair of electrons is often replaced by a long dash. Each dash represents TWO electrons

16. + 7e- 7e- 8e- 8e- F F F F F F F F lonepairs lonepairs single covalent bond single covalent bond lonepairs lonepairs Why should two atoms share electrons? To get a valence of 8 electrons! Lewis structure of F2

17. Multiple Covalent Bonds • double bond:covalent bond in which two pairs of electrons are shared between two atoms • shown by two side-by-side pairs of dots or by two parallel dashes

18. Multiple Covalent Bonds • triple bond:covalent bond in which three pairs of electrons are shared between two atoms • shown by three side-by-side pairs of dots or by three parallel dashes

19. Steps for Drawing Lewis Structures • Draw the Lewis Dot diagram for each individual atom • Count up the number of valence electrons • Connect the atoms together to pair up the electrons (put atoms that can make the most connections in the center) • Once all electrons are paired, recount electrons to double check total valence

20. Practice Draw the Lewis Structure for HBr 1. H Br 2. 1 + 7 = 8 3. H — Br 4. 2 + 6 = 8

21. Bond Polarity

22. Review:What is electronegativity? ability of an atom to attract electrons Which element is the most electronegative? Fluorine - Has 7 valence e- and wants 8 H F

23. F H F H Polar bond : covalent bond with greater electron density around one of the two atoms electron poor region electron rich region e- rich e- poor d+ d-

24. 1 18 2 13 14 15 16 17 3 4 5 6 7 8 9 10 11 12

25. Increasing difference in electronegativity Nonpolar Covalent Ionic Polar Covalent transfer e- partial transfer of e- share e- What type of Bond is it?

26. Classify the following bonds as ionic, polar covalent,or covalent: Cs to Cl Cs – 0.7 Cl – 3.0 3.0 – 0.7 = 2.3 Ionic H to S H – 2.1 S – 2.5 2.5 – 2.1 = 0.4 Polar Covalent Cl to N Cl– 3.0 N – 3.0 3.0 – 3.0 = 0 Nonpolar Covalent

27. Intermolecular Forces

28. Intermolecular forces: attractive forces betweenmolecules. Intramolecular forces:attractive forces within a molecule (the bonds) Intermolecular Forces Intramolecular Forces Intramolecular Forces intramolecularforces are much stronger than intermolecular forces

29. Dipoles • What is a dipole? • A polar molecule • Uneven sharing of electrons so there is a separation of charge

30. Dipole-Dipole Forces • Attraction between two polar molecules — — + +

31. Hydrogen Bonding • Special type of Dipole – Dipole • Attraction between:Hydrogen and Nitrogen/Oxygen/Fluorine

32. Dipole – Induced Dipole • Attraction between one polar and one nonpolar molecule — + Electrons shift toward positive end of dipole — — + +

33. London Dispersion Forces • Attraction between two nonpolar molecules Electrons become uneven and form a dipole — — + +

34. Strength of IMF • Hydrogen Bond • Dipole – Dipole • Dipole – Induced Dipole • London Dispersion Forces strongest weakest

35. What does IMF effect? • Viscosity • Surface Tension • Cohesion/Adhesion • Boiling Point

36. Viscosity • Measures a fluid’s resistance to flow Stronger IMF  Higher Viscosity

37. Surface Tension • result of an imbalance of forces at the surface of a liquid. Stronger IMF  Higher Surface Tension

39. Adhesion Cohesion Adhesion and Cohesion • Cohesion: intermolecular attraction between like molecules • Adhesion: intermolecular attraction between unlike molecules

40. Boiling Point • Point at which liquid particles escape the surface of the liquid into the gas phase Stronger IMF  Higher Boiling Point