6.2 – Notes Formation of Ionic Bonds

II. The Formation and Nature of Ionic Bonds A. Formation of an ionic bond Transfer of electrons: sodium reacts with chlorine sodium has 1 valence electron that it transfers to chlorine; Na  1e- + Na+ chlorine is in need of 1 valence electron which it accepts from sodium; Cl + 1e-  Cl-;

Na = oxidized and is therefore the reducing agent Cl = reduced and is therefore the oxidizing agent

One of the best ways to “see” this is to use dot diagrams.   Reduction Reaction: Cl + e-  Cl- Oxidizing Agent = Cl Oxidation Reaction: Na  Na+ + e- Reducing Agent = Na

  Ba I  Ba2+ 2 I- I Reduction Reaction: 2(I + e-  I-) Oxidizing Agent = I *happened twice so put entire equation in ( ) and multiply by 2. Oxidation Reaction: Ba  Ba+2 + 2e- Reducing Agent = Ba

B. Properties of ionic compounds 1. Crystal lattice - when compound forms, (+) and (-) ions are packed into repeating pattern to decrease forces of attraction/repulsion - large #s of (+) and (-) ions exist together in a ratio determined by the # of electrons transferred;

2. Properties - MP, BP, hardness depends on the how strongly the particles are attracted to each other - ionic bonds are strong  high MP, high BP - color related to structure

3. Electrolytes - an electrolyte is a substance that conducts electricity - in order to conduct electricity, electrons must be free to move - ionic compounds can NOT conduct in the solid state, but CAN conduct electricity in solution (dissolved, aqueous) or molten state (b/c e- can move freely)

4. Energy and the ionic bond a. Lattice energy - the energy released when oppositely charged ions (in the gas phase) come together to form a solid (bond making is EXOthermic). Example: The lattice energy of NaCl is the energy released when Na+ and Cl- ions come together to form the lattice of alternating Na+ and Cl- ions in the NaCl crystal; the more negative the lattice energy, the stronger the force of attraction, the more stable the final compound

b. Factors that influence the magnitude of the lattice energy i. Size of ions - smaller ions have a more (-) value (stronger force of attraction) b/c the nucleus is closer to the valence electrons; ion size increases, LE decreases ii. Charges of ions ionic bond formed from the attraction of ions w/ larger (+) or (-) charges has a more (-) value b/c charge is related to # of e- SrCl2 has energy b/t NaCl and MgO b/c it contains ions of different charge values; charge increases, LE increases