Ch. 7 Ionic and Metallic Bonding

7.1 Ions

Valence Electrons Electrons in the highest occupied energy level of an atom Number determines chemical properties of an element Find by looking at group number (1A-8A) Shown in electron dot structures Octet rule: in forming compounds, atoms tend to achieve the electron configuration of a noble gas (fill the octet)

Formation of Cations Positively charged ions are formed when an atom loses one or more valence electrons

Transition Metals Form cations Some form multiple ions (with different charges) Not all achieve pseudo-noble gas configuration

Formation of Anions An atom gains one or more valence electrons

7.2 Ionic Bonds and Ionic Compounds

Formation of Ionic Compounds Ionic compound: composed of cations and anions Electrically neutral (cation and anion charges balance each other) Ionic bond: electrostatic forces that hold ions together in ionic compounds (interaction between cation and anion)

Use electron dot structures to determine formulas of the ionic compounds formed when the following elements react. Potassium and Bromine Sodium and Sulfur Magnesium and Nitrogen Calcium and Chlorine

Formula Units Chemical formulas show the number of atoms of each element in the smallest representative unit of a substance (molecules, formula units, atoms, etc.) Formula unit is the lowest whole number ratio of ions in an ionic compound Between a +1 cation and a -1 anion, the ratio is one-to- one, such as NaCl Between a +2 cation and a -1 anion, the ratio is 1 to 2, such as MgCl2

Water Testing Potassium thiocyanate indicates presence of iron(III) ions if a red color forms Sodium oxalate indicates the presence of calcium ions if a white precipitate forms In both cases, the formation of a new ionic compound indicates the presence of a particular ion in the water.

Properties of Ionic Compounds Crystalline solid at room temperature High melting points Coordination number: number of ions of opposite charge that surround the ion in a crystal Conduct electricity when melted or dissolved in water

7.3 Bonding in Metals

Metallic Bonds Metallic bonds are forces of attraction between free- floating electrons and positively charged metal ions Sea of electrons model Conductivity Malleability

Alloys Mixture of 2+ elements including at least 1 metal Properties are often superior to pure elements Oxidation, hardness, malleability, conductivity Common alloys include stainless steel, sterling silver, and cast iron

Electrolysis Simulation www.binarylabs.info/pearson/chem_sim/index.html