Chapter 6 Ionic Bonds

Types of Bonding Atoms are rarely found individually in nature because atoms try to achieve a more stable structure. Atoms can become stable in one of three ways: By giving electrons to another atom By taking electrons from another atom By sharing electrons with another atom Metallic bonds = metallic atoms combine to form a metallic lattice Ionic bonds = metallic atoms combine with non-metallic atoms Covalent bonds = non-metallic bonds combine

Ions - review Atoms which gain or lose electrons are called ions Positive ions = cations Negative ions = anions

IONIC BONDING Metals and non-metals react because electrons lost by metals are taken up by electronegative non-metals. This transfer of electrons is an ionic bond. Cations and Anions are oppositely charged and attract each other by electrostatic attraction.

IONIC BONDING Note: the bonded ionic compound is more stable than the unbonded form and has different properties from those of the original elements. The general name for an ionic compound (a substance formed from a reaction between a metal and non-metal, is a salt)

Electron Shell Diagrams Using electron shell diagrams and simple equations to show the ionic bonding between a metal and a non-metal: Be and Cl Li and F Al and S Na and N Mg and S Mg and F Mg2+ + 2Cl- MgCl2

Ionic Lattices Major features: Ionic compounds form crystals that are composed of three dimensional arrays of positive metal ions and negative non-metal ions These are called ionic network lattices and are held together by strong electrostatic forces between the oppositely charged particles The ions are arranged in a regular repeating pattern and pack together so that a positive ion is only surrounded by negatives and a negative ion is only surrounded by positive ions The numbers of positive ions and negative ions depend on making the compound neutral

Ionic Lattices Ionic compounds are made up of two ions that have opposing charges. The electrostatic forces of attraction holding them together are strong. As a result, they are: Usually crystalline solids Have high melting and boiling points, as a large amount of energy is needed to separate the ions Will not conduct electricity in the solid state as the ions are not free to move

Ionic Lattices Are hard, since the surface of the crystal is not easily scratched due to the strong ionic bonds Will often dissolve in water to form free mobile ions as water disrupts the rigid crystal structure Will conduct electricity when in solution as ions are free to move. Solution is called an electrolyte. Are brittle, as moving the crystal structure causes ions of like charge to come into contact and the repulsion shatters the structure

Ionic Bonding Polyatomic ions – Some ions contain more than one atom. Eg. Carbonate CO3, Ammonium NH4, Hydroxide OH If more than one of these ions is required then you need to use brackets eg. Mg(OH)2 Ions of elements with different valencies – Some elements form ions with different charges. In this situation, you need to specify the electrovalency by placing the roman numeral of the charge after the metal in the name of the compound. Eg. Iron (II) Chloride contains the Fe2+ ion, formula is FeCl2 Iron (III) Chloride contains the Fe3+ ion, formula is FeCl3