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Chapter 8

Chapter 8. Covalent Bonding. National Standards for Chapter 8. UCP.2 Evidence, models, and explanation UCP.3 Change, constancy, and measurement UCP.5 Form and function A.1 Abilities necessary to do scientific inquiry A.2 Understandings about scientific inquiry

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Chapter 8

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  1. Chapter 8 Covalent Bonding

  2. National Standards for Chapter 8 • UCP.2 Evidence, models, and explanation • UCP.3 Change, constancy, and measurement • UCP.5 Form and function • A.1 Abilities necessary to do scientific inquiry • A.2 Understandings about scientific inquiry • B.1 Structure of atoms • B.2 Structure ad properties of matter • B.3 Chemical reactions • B.4 Motions and forces • B.6 Interactions of energy and matter • E.2 Understandings about science and technology • G.2 Nature of scientific knowledge • G.3 Historical perspectives

  3. Vocabulary/Study Guide • Define each term using the Glossary • Either write on the handout, or use your own paper • This is due on Test Day (tentatively, Tuesday, February 4)

  4. Section 1: The Covalent Bond • National Standards: • UCP.2 Evidence, models, and explanation • UCP.3 Change, constancy, and measurement • UCP.5 Form and function • A.1 Abilities necessary to do scientific inquiry • B.1 Structure of atoms • B.2 Structure ad properties of matter • B.3 Chemical reactions • B.4 Motions and forces • B.6 Interactions of energy and matter

  5. Objectives – Section 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. REVIEW VOCABULARY: chemical bond:the force that holds two atoms together

  6. New Vocabulary covalent bondpi bond moleculeendothermic reaction Lewis structureexothermic reaction sigma bond Atoms gain stability when they share electrons and form covalent bonds.

  7. Launch Lab • OBJECTIVE: Students will compare the properties of organosilicon oxide (Si(OCH2CH3)2O) to the properties of ionic compounds, which they studied previously. • PREDICTIONS: • What type of compound is used to make a super ball? • If you vary the amount of ethanol used in making the ball, how will this effect the outcome? • DATA:

  8. Why Do Atoms Bond? • Noble gases have stable electron arrangements. • This stable arrangement consists of a full outer energy level and has lower potential energy than other electron arrangements. • Metals and nonmetals gain stability by transferring electrons (gaining or losing) to form ions that have stable noble-gas electron configurations. • The octet rule states that atoms with a complete octet, a configuration of eight valence electrons, are stable

  9. Why Do Atoms Bond? • Another way atoms can gain stability is by sharing valence electrons with other atoms, which also results in noble-gas electron configurations. • The stability of an atom, ion, or compound is related to its energy. • That is, lower energy states are more stable.

  10. What is a Covalent Bond? • 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 which are near each other on the periodic table.

  11. What is a Covalent Bond? • Diatomic molecules (H2, N2, F2, O2, I2, Cl2, Br2) exist because the two-atom molecules are more stable than the individual atoms.

  12. What is a Covalent Bond? • The most stable arrangement of atoms exists at the point of maximum net attraction, where the atoms bond covalently and form a molecule.

  13. Lab: Compare Melting Points, pg. 242 • OBJECTIVE: To observe how the properties of a compound depend on whether the bonds in the compound are ionic or covalent. • PREDICTIONS: • How can you determine the relationship between bond type and melting point? • Predict the order in which salt, sugar, and paraffin will melt. • DATA:

  14. 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.

  15. Single Covalent Bonds • Electron-dot diagrams can be used to show valence electrons of atoms • In a Lewis structure electron-dot diagrams and a line are used to symbolize the valence electrons and 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.

  16. Single Covalent Bonds • The halogens—the group 17 elements—have 7 valence electrons and form single covalent bonds with atoms of other non-metals.

  17. Single Covalent Bonds • 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 .

  18. Single Covalent Bonds • Atoms in group 15 form three single covalent bonds, such as in ammonia.

  19. Single Covalent Bonds • Atoms of group 14 elements form four single covalent bonds, such as in methane.

  20. Single Covalent Bonds • Practice Problems #1-6, page 244 • Write the problem, then the answer

  21. Single Covalent Bonds • Sigma bondsare single covalent bonds represented by the Greek letter sigma (σ). • Sigma bonds occur when the pair of shared electrons is in an area centered between the two atoms.

  22. 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.

  23. Multiple Covalent Bonds • A multiple covalent bond consists of one sigma bond and at least one pi bond. • The pi bond(π)is 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.

  24. The Strength of Covalent Bonds • The strength depends on the distance between the two nuclei, or bond length. • As length increases, strength decreases.

  25. The Strength of Covalent Bonds • 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.

  26. The Strength of Covalent Bonds • 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.

  27. Homework, Section 1 • SECTION 1 REVIEW, Page 247 • Questions #7,8,9,12,13 • Answer with complete sentences • Due tomorrow • Also due: • Worksheet 8.1 • And Practice Problems, #1-6, page 244

  28. Section 2: Naming Molecules • National Standards: • UCP.2 Evidence, models, and explanation • UCP.3 Change, constancy, and measurement • UCP.5 Form and function • B.2 Structure and properties of matter • G.2 Nature of scientific knowledge

  29. Objectives – Section 2 • Translatemolecular formulas into binary molecular compound names. • Nameacidic solutions. Review Vocabulary: oxyanion:a polyatomic ion in which an element (usually a nonmetal) is bonded to one or more oxygen atoms

  30. New Vocabulary oxyacid Specific rules are used when naming binary molecular compounds, binary acids, and oxyacids.

  31. 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.

  32. Naming Binary Molecular Compounds • Prefixes are used to indicate the number of atoms of each element in a compound.

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

  34. Naming Binary Molecular Compounds • Practice Problems #14-18, page 249

  35. Math Skills Transparency 9

  36. 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.

  37. Naming Acids • 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.

  38. Naming Acids

  39. Naming Acids • An acid, whether a binary acid or an oxyacid, can have a common name in addition to its compound name.

  40. Naming Acids • Practice Problems #19-24, page 251

  41. Naming Acids • The name of a molecular compound reveals its composition and is important in communicating the nature of the compound.

  42. Naming Acids • Practice Problems #25-30, page 251

  43. Naming Acids

  44. Homework, Section 2 • SECTION 2 REVIEW, Page 252 • Questions #31-36 • Answer with complete sentences • Due tomorrow

  45. Section 3: Molecular Structures • National Standards: • UCP.2 Evidence, models, and explanation • UCP.3 Change, constancy, and measurement • UCP.5 Form and function • B.2 Structure and properties of matter

  46. Objectives – Section 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. Review Vocabulary: ionic bond:the electrostatic force that holds oppositely charged particles together in an ionic compound

  47. New Vocabulary structural formula resonance coordinate covalent bond Structural formulas show the relative positions of atoms within a molecule.

  48. Structural Formulas • A structural formulauses letter symbols and bonds to show relative positions of atoms.

  49. Structural Formulas • 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.

  50. Structural Formulas • 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.

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