Chapter 6: Chemical Bonding

1. Chapter 6: Chemical Bonding

2. Chemical Bond Mutual attraction between the nuclei and valence electrons of different atoms that binds the atoms together. Why do atoms form bonds?

3. Electronegativity The extent to which an atom attracts electrons it shares with another atom. For two bonding atoms, the greater the electronegativity difference the greater the degree of ionic character in the bonds. If the EN difference is 1.7 or more, then the compound is said to be ionic. If the difference is smaller, then it is classified as covalent.

4. Using Electronegativity Use ?EN to classify these compounds as covalent or ionic: NH3 NaCl O2 BaCl2 H2O BaO

5. Ionic Bond  An ionic bond is the resulting attraction for an anion and a cation after an electron is transferred from the metal to the non-metal.

6. Ionic Bond Electrostatic attraction of oppositely charged particles. Formula Unit = smallest collection of ions; provides the formula e.g. NaF, MgO Electron dot notations can be used to show why an ionic bonds form

7. Formation of NaF

8. Formation of MgO

9. Ionic Solids Dissociate in Water

10. Properties of Ionic Compounds Solids at room temperature Nonconductive as solids Dissolve in water by dissociation Conductive when dissolved High melting points Hard, Brittle Crystals

11. Polyatomic Ions Charged group of covalently bonded atoms. Bonds ionically to oppositely charged ions. Examples: nitrate (NO31-), sulfate (SO42-), ammonium (NH4+), phosphate (PO43-)

12. Covalent Bonds  A covalent bond exists when two electrons are shared by two non-metallic atoms.

13. Covalent Molecules Molecule = neutral group of atoms held together by covalent bond Empirical Formula = simplest ratio of atoms to one another: CH2O Molecular Formula = actual ratio of atoms in molecule: C6H12O6

14. Formation of a Covalent Bond

15. Formation of H2

16. Formation of I2

17. Formation of HCl

18. Polar Bond vs. NonPolar Bond The nonpolar covalent bond has an equal sharing of electrons, while the nonpolar covalent bond has an unequal distribution of charge. A ?EN less than 0.3 indicates a nonpolar covalent bond.

19. H2O has has 2 polar covalent bonds Polar molecules must have polar bonds, and they must be spaced so the molecule has an uneven distribution of charge.

20. Properties of Covalent Molecules Solids, liquids, or gases at room temperature Nonconductive as solids May dissolve in water Dissolve in nonpolar solvents (hexane) Non-conductive when dissolved Low melting points

23. Bond Length & Strength Shorter bonds are stronger than longer bonds. This means it takes more energy to break them. Triple bonds (6 shared electrons) are shorter than double bonds (4 shared electrons). Triple bonds are stronger. Double bonds (4 shared electron) are shorter than single bonds (2 shared electrons).

24. Metallic Bonding Valence electrons in metals are free to move throughout the entire substance. Metals are an ocean of negative charge surrounding kernels of positive charge. (The kernel = the nucleus plus all nonvalance electrons.) The valence electrons of metals are said to be delocalized. Delocalized electrons cause metals to conduct electricity very well. Delocalized electrons also explain metallic luster, malleability, and ductility.

25. Metallic Bonding 

26. Comparison of Two Types of Bonding Covalent Bonds A sharing of two or more electrons between atoms. When two nonmetal atoms combine they do so by the formation of covalent bonds. Ionic Bonds An attraction that occurs between ions of opposite charge. Metals and nonmetals are held together with ionic bonds. Polyatomic ions also form ionic bonds. (e.g. ammonium chloride)

27. EN What is the relationship between electronegativity and the polarity of a chemical bond? Is CCl4 ionic or covalently bonded?

28. Metals What specific property of metals accounts for their unusual electrical conductivity? What are �delocalized electrons�?

29. MC An unknown substance is an excellent electrical conductor in the solid state and is malleable. What type of bonding does this substance exhibit? a. Ionic b. Covalent c. Metallic d. Cannot be determined

30. MC An unknown substance conducts electricity when dissolved in water. It has a melting point of 1200 oC. What type of bonding does this substance exhibit? a. Ionic b. Covalent c. Metallic d. Cannot be determined

31. MC An unknown substance conducts electricity when dissolved in water. It is a soft solid with a melting point of 89 oC. What type of bonding does this substance exhibit? a. Ionic b. Covalent c. Metallic d. Cannot be determined

32. MC A chemical bond results from themutual attraction of nuclei for a. Electrons b. Neutrons c. Protons d. Dipoles

33. MC A polar covalent bond is likely to form between two atoms that a. Are similar in electronegativity b. Are of similar size c. Differ in electronegativity d. Have the same number of electrons

34. MC Which of these compounds is predicted to have the highest boiling point? a. HCl b. Cl2 c. SO2 d. NaCl

35. MC Which atom has the largest radius? a. Cl b. Br c. F d. I

36. MC A bond formed between two elements that have a very large difference in electronegativity is called a. Covalent b. Polar covalent c. Ionic d. Double bond

37. MC To attain a noble gas configuration, an atom of chlorine must a. Gain 2 electrons b. Lose 2 electrons c. Gain 1 electron d. Lose 1 electron

38. MC Which of these statements explains why ionic compounds generally conduct an electric current when dissolved in water? a. The shared electrons become free to move when dissolved in water b. The ions dissociate and become free to move when dissolved in water. c. The compound becomes negatively charged when dissolved in water.

39. Moles of electrons An atom of aluminum forms an ion with a 3+ charge. If 45.6 g of Al atoms are turned into ions, how many moles of electrons are transferred? How many total electrons is this?

40. Moles of electrons Sulfur atoms form �2 anions. If 23.5 grams of Sulfur atoms form into anions, how many moles of electrons do the sulfur atoms gain?