Chapter 8: Covalent Bonding

1. CHEMISTRY Matter and Change Chapter 8: Covalent Bonding

2. Table Of Contents CHAPTER8 Section 8.1 The Covalent Bond Section 8.2 Naming Molecules Section 8.3 Molecular Structures Section 8.4 Molecular Shapes Section 8.5Electronegativity and Polarity Click a hyperlink to view the corresponding slides. Exit

3. The Covalent Bond SECTION8.1 Applythe octet rule to atoms that form covalent bonds. Describethe formation of single, double, and triple covalent bonds. Contrastsigma and pi bonds. Relatethe strength of a covalent bond to its bond length and bond dissociation energy. chemical bond:the force that holds two atoms together

4. The Covalent Bond SECTION8.1 covalent bond molecule Lewis structure sigma bond pi bond endothermic reaction exothermic reaction Atoms gain stability when they share electrons and form covalent bonds.

5. The Covalent Bond SECTION8.1 Why do atoms bond? The stability of an atom, ion or compound is related to its energy: lower energy states are more stable. Metals and nonmetals gain stability by transferring electrons (gaining or losing) to form ions that have stable noble-gas electron configurations. Another way atoms can gain stability is by sharing valence electrons with other atoms, which also results in noble-gas electron configurations.

6. The Covalent Bond SECTION8.1 Why do atoms bond?(cont.) Atoms in non-ionic compounds share electrons. The chemical bond that results from sharing electrons is a covalent bond. A moleculeis formed when two or more atoms bond covalently. The majority of covalent bonds form between atoms of nonmetallic elements.

7. The Covalent Bond SECTION8.1 Why do atoms bond?(cont.) Diatomic molecules (H2, N2, F2, O2, I2, Cl2, Br2) exist because the two-atom molecules are more stable than the individual atoms.

8. The Covalent Bond SECTION8.1 Why do atoms bond?(cont.) The most stable arrangement of atoms exists at the point of maximum net attraction, where the atoms bond covalently and form a molecule.

9. The Covalent Bond SECTION8.1 Single Covalent Bonds When only one pair of electrons is shared, the result is a single covalent bond. The figure shows two hydrogen atoms forming a hydrogen molecule with a single covalent bond, resulting in an electron configuration like helium.

10. The Covalent Bond SECTION8.1 Single Covalent Bonds(cont.) In a Lewis structure dots or a line are used to symbolize a single covalent bond. • The halogens—the group 17 elements—have 7 valence electrons and form single covalent bonds with atoms of other non-metals.

11. The Covalent Bond SECTION8.1 Single Covalent Bonds(cont.) Atoms in group 16 can share two electrons and form two covalent bonds. Water is formed from one oxygen with two hydrogen atoms covalently bonded to it .

12. The Covalent Bond SECTION8.1 Single Covalent Bonds(cont.) Atoms in group 15 form three single covalent bonds, such as in ammonia.

13. The Covalent Bond SECTION8.1 Single Covalent Bonds(cont.) Atoms of group 14 elements form four single covalent bonds, such as in methane.

14. The Covalent Bond SECTION8.1 Single Covalent Bonds(cont.) Sigma bondsare single covalent bonds. Sigma bonds occur when the pair of shared electrons is in an area centered between the two atoms.

15. The Covalent Bond SECTION8.1 Multiple Covalent Bonds Double bonds form when two pairs of electrons are shared between two atoms. Triple bonds form when three pairs of electrons are shared between two atoms.

16. The Covalent Bond SECTION8.1 Multiple Covalent Bonds(cont.) A multiple covalent bond consists of one sigma bond and at least one pi bond. The pi bondis formed when parallel orbitals overlap and share electrons. The pi bond occupies the space above and below the line that represents where the two atoms are joined together.

17. The Covalent Bond SECTION8.1 The Strength of Covalent Bonds The strength depends on the distance between the two nuclei, or bond length. As length increases, strength decreases.

18. The Covalent Bond SECTION8.1 The Strength of Covalent Bonds(cont.) The amount of energy required to break a bond is called the bond dissociation energy. The shorter the bond length, the greater the energy required to break it.

19. The Covalent Bond SECTION8.1 The Strength of Covalent Bonds(cont.) An endothermic reactionis one where a greater amount of energy is required to break a bond in reactants than is released when the new bonds form in the products. An exothermic reactionis one where more energy is released than is required to break the bonds in the initial reactants.

20. Section Check SECTION8.1 What does a triple bond consists of? A.three sigma bonds B.three pi bonds C.two sigma bonds and one pi bond D.two pi bonds and one sigma bond

21. Section Check SECTION8.1 Covalent bonds are different from ionic bonds because: A.atoms in a covalent bond lose to another atom B.atoms in a covalent bond do not have noble-gas electron configurations C.atoms in a covalent bond share electrons with another atom D.atoms in covalent bonds gain electrons from another atom

23. Naming Molecules SECTION8.2 Translatemolecular formulas into binary molecular compound names. oxyanion:a polyatomic ion in which an element (usually a nonmetal) is bonded to one or more oxygen atoms Nameacidic solutions. oxyacid Specific rules are used when naming binary molecular compounds, binary acids, and oxyacids.

24. Naming Molecules SECTION8.2 Naming Binary Molecular Compounds • Ex. N2O • The first element is always named first using the entire element name, N is the symbol for nitrogen. • The second element is named using its root and adding the suffix -ide, O is the symbol for oxygen so the second word is oxide. • Prefixes are used to indicate the number of atoms of each element that are present in the compound, There are two atoms of nitrogen and one atom of oxygen so the first word is dinitrogen and the second word is monoixide.

25. Naming Molecules SECTION8.2 Naming Binary Molecular Compounds(cont.) Prefixes are used to indicate the number of atoms of each element in a compound.

26. Naming Molecules SECTION8.2 Naming Binary Molecular Compounds(cont.) Many compounds were discovered and given common names long before the present naming system was developed (water, ammonia, hydrazine, nitric oxide).

27. Naming Molecules SECTION8.2 Naming Acids • Binary Acids (An acid that contains hydrogen and one other element) – Ex. HCl • The first word has the prefix hydro- to name the hydrogen part of the compound. The rest of the word consists of a form of the root of the second element plus the suffix–ic, HCl (hydrogen and chlorine) becomes hydrochloric. • The second word is always acid, Thus, HCl in a water solution is called hydrochloric acid.

28. Naming Molecules SECTION8.2 Naming Acids(cont.) • An oxyacid is an acid that contains both a hydrogen atom and an oxyanion. Ex. HNO3 • Identify the oxyanion present. The first word of an oxyacid’s name consists of the root of the oxyanion and the prefix per- or hypo- if it is part of the name and a suffix. If the oxyanion’s name ends with the suffix –ate, replace it with the suffix –ic. If the name of the oxyanion ends with suffix –ite, replace it with suffix –ous, NO3 the nitrate ion, becomes nitric. • The second word of the name is always acid, HNO3 (hydrogen and nitrogen ion) becomes nitric acid.

29. Naming Molecules SECTION8.2 Naming Acids(cont.)

30. Naming Molecules SECTION8.2 Naming Acids(cont.) An acid, whether a binary acid or an oxyacid, can have a common name in addition to its compound name.

31. Naming Molecules SECTION8.2 Naming Acids(cont.) The name of a molecular compound reveals its composition and is important in communicating the nature of the compound.

32. Naming Molecules SECTION8.2 Naming Acids(cont.)

33. Section Check SECTION8.2 Give the binary molecular name for water (H2O). A.dihydrogen oxide B.dihydroxide C.hydrogen monoxide D.dihydrogen monoxide

34. Section Check SECTION8.2 Give the name for the molecule HClO4. A.perchloric acid B.chloric acid C.chlorous acid D.hydrochloric acid

36. Molecular Structures SECTION8.3 Listthe basic steps used to draw Lewis structures. Explainwhy resonance occurs, and identify resonance structures. Identifythree exceptions to the octet rule, and name molecules in which these exceptions occur. ionic bond:the electrostatic force that holds oppositely charged particles together in an ionic compound

37. Molecular Structures SECTION8.3 structural formula resonance coordinate covalent bond Structural formulas show the relative positions of atoms within a molecule.

38. Molecular Structures SECTION8.3 Structural Formulas A structural formulauses letter symbols and bonds to show relative positions of atoms.

39. Molecular Structures SECTION8.3 Structural Formulas(cont.) Drawing Lewis Structures • Predict the location of certain atoms, the atom that has the least attraction for shared electrons will be the central atom in the molecule (usually, the one closer to the left side of the periodic table). All other atoms become terminal atoms. Note: Hydrogen is always a terminal atom. • Determine the number of electrons available for bonding, the number of valence electrons. • Determine the number of bonding pairs, divide the number of electrons available for bonding by two.

40. Place the bonding pairs, place a single bond between the central atoms and each of the terminal atoms. Determine the number of bonding pairs remaining, Subtract the number of bonding pairs in step 4 from the number of bonding pairs in step 3. Place lone pairs around terminal atoms, except hydrogen, to satisfy the octet rule. Any remaining pairs will be assigned to the central atom. Determine whether the central atom satisfies the octet rule, If not, convert one or two of the lone pairs on the terminal atoms into a double bond or a triple bond between the terminal atom and the central atom. Remember: carbon, nitrogen, oxygen and sulfur often form double and triple bonds. Molecular Structures SECTION8.3 Structural Formulas(cont.)

41. Molecular Structures SECTION8.3 Structural Formulas(cont.) Atoms within a polyatomic ion are covalently bonded. The procedure for drawing Lewis structures is similar to drawing them for covalent compounds. Difference is, you need to determine the number of electrons available for bonding, find the number of electrons available in the atoms present and then subtract the ion charge if the ion is positive or add the ion charge if the ion is negative.

42. Molecular Structures SECTION8.3 Resonance Structures Resonanceis a condition that occurs when more than one valid Lewis structure can be written for a molecule or ion. This figure shows three correct ways to draw the structure for (NO3)-1.

43. Molecular Structures SECTION8.3 Resonance Structures(cont.) Two or more correct Lewis structures that represent a single ion or molecule are resonance structures. The molecule behaves as though it has only one structure. The bond lengths are identical to each other and intermediate between single and double covalent bonds.

44. Molecular Structures SECTION8.3 Exceptions to the Octet Rule Some molecules do not obey the octet rule. A small group of molecules might have an odd number of valence electrons. NO2 has five valence electrons from nitrogen and 12 from oxygen and cannot form an exact number of electron pairs.

45. Molecular Structures SECTION8.3 Exceptions to the Octet Rule(cont.) • A few compounds form stable configurations with less than 8 electrons around the atom—a suboctet. A coordinate covalent bond forms when one atom donates both of the electrons to be shared with an atom or ion that needs two electrons.

46. Molecular Structures SECTION8.3 Exceptions to the Octet Rule(cont.) A third group of compounds has central atoms with more than eight valence electrons, called an expanded octet. Elements in period 3 or higher have a d-orbital and can form more than four covalent bonds.

47. Section Check SECTION8.3 What is it called when one or more correct Lewis structures can be drawn for a molecule? A.suboctet B.expanded octet C.expanded structure D.resonance

48. Section Check SECTION8.3 Where do atoms with expanded octets occur? A.transition metals B.noble gases C.elements in period 3 or higher D.elements in group 3 or higher

50. Molecular Shapes SECTION8.4 Summarizethe VSEPR bonding theory. atomic orbital:the region around an atom’s nucleus that defines an electron’s probable location Predictthe shape of, and the bond angles in, a molecule. Definehybridization. VSEPR model hybridization The VSEPR model is used to determine molecular shape.