In the Na-Cl reaction, Na donates one valence electron to Cl. Cl accepts one electron from Na. Both Na + and Cl - have the electron configurations of noble gases after the reaction. The electrostatic force between these oppositely charged ions holds them together Ionic bond is formed. Due to this ionic bond, Na + and Cl - form an ionic compound. Compounds that contain ionic bonds are ionic compounds. 3
Binary Ionic Compounds: Thousands of compounds contain ionic bonds. Many ionic compounds are binary, which means that they contain only two different elements. Binary ionic compounds contain a metallic cation and a nonmetallic anion. Example: NaCl and MgO are binary ionic compounds. 4
The charges of ions are important in the formation of ionic compounds. The number of electrons accepted and donated are equal. The total charge of an ionic compound is zero. Therefore, the ionic compound formed by X +m and Y -n can be written as: X n Y m. 5 Example: What is the ionic compound formed by Ca and F? Cation: Ca +2 Anion: F - Ionic compound formed: CaF 2
Example: What is the ionic compound formed by Al and O? 6 Cation: Al +3 Anion: O -2 Ionic compound formed: Al 2 O 3
Lecture 33 Properties of Ionic Compounds Ozgur Unal 7
In an ionic compound, large number of positive and negative ions exist together. These ions are packed into a regular repeating pattern that balances the forces of attraction and repulsion between the ions. Example: NaCl crystal Each Na is surrounded by 6 Cl, an each Cl is surrounded by 6 Na. Figure 7.7 8
9 The strong attraction among the positive ions and negative ions in an ionic compound result in the formation of a crystal lattice. A crystal lattice is a 3-dimensional geometric arrangement of particles. Minerals in Figure 7.8 have crystal lattice structure. There are thousands of minerals and mineralogists classify them according to their color, hardness, magnetic and electric structure etc. The types of anions minerals contain can also be used to identify minerals. Example: Silicates (Si and O), Carbonates (C and O), Borates (B) etc.
Examples of physical properties: Melting point Boiling point Hardness Electrical conductivity etc. 10 Electrical conductivity depends on the freely moving charged particles. Ions are charged particles. In solid state, ions cannot move freely, therefore ionic solids cannot conduct electricity.
What happens when you put table salt in water? 11 Salty water and liquid salt conduct electricity. Because in both cases there are ions that can move freely. Similarly, some other ionic compounds dissolved in water, or their liquid state conduct electricity. An ionic compound whose aqueous solution conducts an electric current is salled an electrolyte. Does the solution conduct electric current?
Check out Table 7.5 Ionic bonds are strong, therefore the melting and boiling points of ionic compounds are high. 12 Ionic crystals are also hard, rigid and brittle because of the strong attractive forces that hold the ions in place. It is possible to break these ionic bonds by applying a force on the crystal structure. Check out Figure 7.9
Chemical reactions can be exothermic and endothermic. Exothermic reactions releases energy. Example: burning a paper Endothermic reactions require energy. Example: chemical reactions when cooking food 13 Formation of ionic bonds release energy, therefore those chemical reactions are exothermic. Breaking ionic bonds require energy, therefore it is endothermic.
The energy required to separate 1 mol of the ions of an ionic compound is called the lattice energy. Mol is a unit for amount of substance. Check out Table 7.6 14 Lattice energy depends on: The size of the ions bonded Charge of the ions Ionic compounds with smaller ions have greater lattice energy. Ionic compounds of ions with greater charge have greater lattice energy.