Chemical Bonding IONIC BONDS NOV. 21

Ionic Bonds  Characterized by a transfer of electrons  When electrons are transferred between atoms ions are produced having opposite charges  The attraction of oppositely charged ions holds them together  This electrostatic attraction is the ionic bond

Ionic Bonds- Example An example of a substance having ionic bonds is NaCl, sodium chloride. (Watch the bond being formed in the demonstration below) NaCl Na Cl

Ionic Bonds - Forming NaCl  Sodium is in Group 1, so it has one valence electron 1s 2 2s 2 2p 6 3s 1  Chlorine is in Group 17 and has seven valence electrons 1s 2 2s 2 2p 6 3s 2 3p 5

 The valence electrons of the Na and Cl atoms rearrange to give each atom a noble gas configuration of valence electrons  If the one valence electron of sodium is transferred to the chlorine atom, chlorine becomes stable with an octet of electrons. 1s 2 2s 2 2p 6 3s 2 3p 6  The sodium also becomes stable because it’s outer energy level is now the 2nd with eight electrons. 1s 2 2s 2 2p 6 Ionic Bonds - Forming NaCl

 Because the chlorine atom now has an extra electron, it has a negative charge  Negatively charged ions are called anions  Because sodium lost an electron, it now has an unbalanced proton in the nucleus and therefore has a positive charge  Positively charged ions are called cations  The charge on an ion is called its oxidation number or oxidation state Ionic Bonds - Forming NaCl

 A compound that is composed of ions is called an ionic compound  Note that only the arrangement of electrons has changed  Nothing about the atom’s nucleus has changed Ionic Bonds - Forming NaCl

Check for Understanding 1.Write out the configuration for a magnesium ion. 2. Predict the charge on a magnesium ion. 3. How many electrons has it lost? 4. Write out the electron configuration for a Sulfur ion. 5. Predict the charge on a sulfur ion. 6. How many electrons has it gained? 7. What would the resulting compound look like? 1s 2 2s 2 2p 6 (the same as Ne) Mg +2 2 e - 1s 2 2s 2 2p 6 3s 2 3p 6 S -2 2 e - MgS

Characteristics of Ionic Compounds:  High melting points  Conduct electricity in the liquid & gaseous states  Considered electrolytes: soluble in water and conduct electricity when dissolved in water  Usually crystallize as sharply defined particles  They are typically composed of a metal and a nonmetal

 Composed of well-organized, tightly bound ions  Form strong, three-dimensional crystal structure  Crystalline solids at room temperature  Positive ions are surrounded by negative ions, and negative ions by positive ions  Resulting structure is called a crystal lattice and contains a regular, repeating, three-dimensional arrangement of ions Crystal Structure of Ionic Compound

Lattice Energy  Energy required to separate one mole of the ions of an ionic compound and is expressed as a negative quantity  The greater (that is, the more negative) the lattice energy is, the stronger the force of attraction between ions  Lattice energy tends to be greater for more- highly-charged ions and for small ions than for ions of lower charge or large size

Check for Understanding 1. What is involved in an ionic bond? 2. What are the types of particles formed? 3. What actually is the ionic bond? 4. Give two characteristics of ionic compounds. 5. What two classes of elements are ionic compounds usually composed of? 6. Describe the arrangement of particles in an ionic crystal and what is the resulting structure called

1. TRANSFER OF ELECTRONS 2. IONS 3. ELECTROSTATIC ATTRACTION 4. HIGH MELTING PTS, CRYSTALLINE STRUCTURE 5. METAL AND NONMETAL 6. HIGHLY ORGANIZED CRYSTALLINE LATTICE