Chapter 4 Chemical Bonds I: The ionic bonds Family – same # of valence (outer) shell electrons Outer shell electrons are call valence electrons For representative elements, valence electrons are outer s and outer p electrons. Group number = number of valence electrons

Lewis (electron) dot structure– shows the number of valence electrons in an atom. Figure 4.1 Lewis Symbols for Selected Representative and Noble-Gas Elements

Compounds and Chemical Bonding A compound consists of more than one element. Elements combine to form compounds. Example - Na + Cl + Na + Cl Cl + Cl Cl2 H + H H2 He, Ne, etc are stable 8 valence electrons (octet rule) I. Ionic compounds A. Formation of ionic compounds Na + Cl

2 Na 8 Cl 7 2 8

+ - 2 Na 8 Cl 8 2 8 cation anion Octet rule

Mg + O ? Mg2+ + O Mg O Mg + O MgO Ca + Cl - Lewis structure 2- Mg + O ? Mg2+ + O Lewis structure Mg O Mg + O MgO One formula unit Ca + Cl 2+ - - Lewis structure

Ca Ca P 3 2 2+ 3- 3 2 B. Properties of ionic compounds High melting point Conduct electricity when dissolved in water

Isoelectronic Species C. Electron configuration of ions Na + 1s2 2s2 2p6 3s1 2+ Ca Cl- O2- 1s2 2s2 2p6 3s2 3p6 4s2 Isoelectronic Species Example: Na+ O-2

Figure 4.5 Two-dimensional cross section of an ionic solid (NaCl). No molecule can be distinguished in this structure. Instead, we can recognize a basic formula unit that is repeated indefinitely.

Na+ Cl- attractive force Ionic bond Fig. 4.1

NaCl (sodium chloride) Na (sodium) chlorine

D. Naming ionic compounds a) Name of positive ions 1) monatomic positive ions – name of the element Na+ sodium ion K+ potassium ion fixed charge (Fig 4.8) Ca2+ calcium ion etc. Systematic name Common name Cu+ copper (I) ion cuprous ion Cu2+ copper (II) ion cupric ion Fe2+ Iron (II) ferrous ion Fe3+ Iron (III) ferric ion

Figure 4.8 A periodic table in which the metallic elements that exhibit a fixed ionic charge are highlighted.

2) Polyatomic positive ions ammonium ion b) Negative ions 1) monatomic 2) polyatomic (Table 4.3)

Names of Selected Common Nonmetallic Ions. Monatomic negative ions

Table 4.3 Common Polyatomic Ions.

c) Name and formula of ionic compounds NaCl sodium chloride MgBr2 magnesium bromide Mg2+ Br- ammonium sulfate

calcium nitrate iron(II) phosphate barium bisulfate

Use of noble gases He balloon Blimps – save neon light O2 + He for Scuba divers

Important ions in the body Function too much – high blood pressure Na+ outside the cell regulation and control of body fluids regulation of body fluids and cellular functions K+ inside the cell prevents high blood pressure Ca2+ outside the cell 90% in bone and teeth major cation in bone Ca3(PO4)2, CaCO3. regulate muscle contraction Lack – muscle cramp, osteoporosis Mg2+ Outside the cell muscle and nerve control

function Cl- Same as Na+ Fe2+ formation of hemoglobin, enzyme, bind to O2 F- tooth formation and retention of Ca2+ in bones Cu2+ enzyme Zn2+ enzyme

In addition to the first 20 elements, memorize names and symbols of the following elements Cr Mn Fe Cu Zn Mo Ag Cd Pt Au Hg Pb Sr Ba Br I Zn2+ Cd2+ Ag+