Chapter 4 Chemical Bonding: The Ionic Bond Model

Transcription

1 Chapter 4 Chemical Bonding: The Ionic Bond Model 1

2 2 Ch 4.1 Chemical Bonds A chemical bond is the attractive force that holds two atoms together in a more complex unit. Ionic Bond electron transfer between atoms formation of ions ionic compounds Covalent Bond sharing of electrons between atoms molecules

3 3 Properties Ionic compounds Very m.p. & b.p. Crystalline solids, salts Good conductors of electricity as liquids or in solution Molecular compounds Much m.p. & b.p. Gases, liquids, or low m.p. solids Do Not conduct electricity demo: compare electrical conductivity in solution

4 4 The type of a chemical bond is determined by: Valence shell electron configuration Ionization energies Electronegativities Recall from Ch 3 that a valence electron is an electron in the outermost electron shell (valence shell) of a representative element (this includes the noble gases). In Chem only electrons in orbitals are considered valence electrons.

5 5 Ch 4.2 Valence Electrons and Lewis Symbol This topic was covered as part of Ch 3.7. Please remember that you must depict unpaired electrons as single dots and paired electrons as pairs of dots. Please note that in your textbook, including Fig 4.1, this rule is not obeyed and that some of the symbols are considered incorrect in this course.. examples Ca : correct Ca incorrect.. Al : correct Al incorrect

6 6 Electron transfer between atoms yields electrically charged ions. Fig 4.3 Positively charged ions = cations Negatively charged ions = anions

7 7 Ch 4.3 The Octet Rule The valence electron configurations of the noble gases are the most stable of all valence electron configurations. All noble gases except have 8 valence electrons. An atom may achieve an octet by gaining, losing, or sharing valence electrons. Na 1s 2 2s 2 2p 6 3s 1 loses 1 valence e Na + 1s 2 2s 2 2p 6 to obtain the electron configuration of Ne 1s 2 2s 2 2p 6 Cl 1s 2 2s 2 2p 6 3s 2 3p 5 adds this e Cl - 1s 2 2s 2 2p 6 3s 2 3p 6 Ar 1s 2 2s 2 2p 6 3s 2 3p 6

8 8 Ch 4.4 Ionic Bond Model & Ch. 4.5 Magnitude of Charge Metals lose valence electrons to form cations Na + K + Ca 2+ Mg 2+ Al 3+ Group IA IIA IIA Nonmetals either share electrons or they gain valence electrons to form anions Cl - Br - O 2- S 2- N 3- Group VIIA VIA VA The chemical properties of an ion are different than for its corresponding neutral atom. Li Li + Ca Ca 2+ lithium lithium ion calcium calcium ion

9 9 Isoelectronic Species are an atom and ion, or two ions, that have the same electron configuration. The following ions are isoelectronic with 1s 2 2s 2 2p 6 10 electrons N 3- O 2- F - Na + Mg 2+ Al 3+ # p increasing nuclear charge (Z) decreasing atomic radii

10 10 Supplemental Material Ionic Radii of Ions of Representative Elements Atom Cation + e Radius Atom + e Anion Radius

11 11 Ch 4.6 & 4.7 Lewis Structures and Chemical Formulas for Ionic Compounds Na + Cl : Na + : Cl : NaCl Ba : + Br : + Br : Ba + 2 : Br : Electron Loss = Electron Gain Electrons/charges must balance to form neutral compounds

12 Drill Problem: Determine the chemical formula for the ionic compound containing the ions of aluminum and sulfur 12

13 13 Ch 4.8 The Structure of Ionic Compounds The electrostatic attractions between the oppositely charged ions hold ionic compounds together. Fig 4.4 The formula unit is the smallest whole-number ratio of ions present in an ionic compound with charge neutrality. Formular unit =

14 14 Ch 4.9 Recognizing and Naming Binary Ionic Compounds Binary = only two elements are present Binary ionic compounds NaCl MgBr 2 K 3 N metal + nonmetal ionic compound cation anion Binary but NOT ionic covalent molecules

15 15 NaCl sodium chloride full name of metallic element (without the term ion) + stem name and suffix of nonmetallic element name BaS barium sulfide Table 4.2 Names of selected common nonmetallic ions

16 Figure 4.8 Metal ions with fixed ionic charge 16

17 17 Some metal ions have variable ionic charges. Figure 4.7 When we name compounds that contain metals with variable ionic charges, the charge on the metal ion must be specified. Copper (I) oxide Cu 2 O copper (I) Cu + Copper (II) oxide CuO copper (II) Cu 2+ Iron (II) chloride FeCl 2 iron (II) Iron (III) chloride FeCl 3 iron (III)

18 18 Drill problem: Name the following compound PbS 2

19 19 Ch 4.10 Polyatomic Ions NO 3 - charge # of atoms nitrate

20 20 Table 4.3 Formulas and Names of Some Common Polyatomic Ions You need to know these polyatomic anions plus the corresponding ions for bromine and iodine.

21 21 Simple steps to memorization. 1. Memorize all ate NO 3 - ClO PO 4 SO 4 nitrate chlorate phosphate sulf 2. One Oxygen less ite suffix NO 2 - nitrite ClO 2 - chlor 3. One Oxygen more than ate per prefix ClO 4 - perchlorate 4. One Oxygen less than ite hypo prefix ClO - hypochlorite

22 22 5. Addition of H + to 2- or 3- ions CO 3 2- carbonate + HCO 3 - bicarbonate hydrogencarbonate Note the change in the charge of the ion

23 23 Summary for ions of sulfur S 2-2- SO 4 2- SO 3 - HSO 4 - HSO 3 sulf sulf sulf sulfate or hydrogensulfate sulfite or hydrogensulfite

24 24 Ch 4.11 Chemical Formulas and Names for Ionic Compounds Containing Polyatomic Ions Fe(OH) 3 iron (III) hydroxide NH 4 NO 3 ammonium (NH 4 ) 2 CO 3 ammonium carbonate

25 25 Name the following compounds CuSO 4 copper sulfate KClO 4 potassium perchlorate Na 3 PO 4 sodium phosphate

26 26 Write the chemical formula for magnesium bisulfite + HSO 3 -

27 27 Write the chemical formula for iron (II) phosphate + PO 4 3-