Chapter 7

 An ion is an atom that has gained or lost electrons from the valence shell.  Valence electrons are the electrons contained in the highest occupied energy level ◦ These electrons will mostly determine the chemical properties of the element ◦ For representative elements, group # = # valence electrons ◦ Exception is Helium with 2 valence e-

 Diagrams that show the number of valence electrons  Also called Lewis Dot Diagrams

 Gilbert Lewis recognized that Noble Gases are inert.  These elements have a full s and p sublevel and with the exception of Helium have 8 valence e-.  He realized that atoms will bond in order to achieve noble gas e- configuration.  Atoms of metals tend to lose their valence e-, leaving a complete octet in the next lowest energy level. Atoms of nonmetals tend to gain e- or to share e- with one another to complete an octet. Magic # = 8

 An atom’s loss of valence e- produces a cation, or (+) charged ion.  Metals have relatively low ionization energy. It requires less energy to remove 1,2,3, or 4 valence electrons.  Metals have relatively low electronegativity and are not likely to gain electrons.  Metals will typically lose all valence electrons and have a charge equal to the number of electrons lost.

 Atoms will lose valence e- in order to achieve the electron configuration of the nearest noble gas. e- configuration for Ne

 Transition metals do not always form Noble gas electron configuration when forming cations.  Because of the partially filled d sublevel, they form pseudo noble gas configurations  Silver will form a +1 ion  Copper can form +1 or +2

 Once electrons are removed from a neutral atom a positive charge will exist.  For cations, the name of the metal is the same as the name of the cation.  Al is called aluminum.  Al +3 is still called aluminum.

 The gain of negatively charged electrons by a neutral atom produces an anion.  Most nonmetals have more than 4 e- in the valence shell.  They will gain e- in order to achieve the noble gas configuration of the nearest noble gas.

 When atoms from group 7A gain e-, they will have a charge of -1. These anions are called halide ions.  Once a nonmetal gains electrons, the name of the ion will be different from the name of the neutral ion.  For monatomic anions, drop the ending and add –ide.  Ex: Oxide, Phosphide, Sulfide, Fluoride, Chloride

 Compounds composed of cations and anions are called ionic compounds.  Ionic compounds are typically neutral.  The electrostatic forces that hold ionic compounds together are called ionic bonds.  Just like when forming ions, ionic compounds consist of cations and anions seeking a complete octet.

 A chemical formula shows the kinds and numbers of atomic in the smallest representative unit of a substance.  Ionic compounds are not typically found as just one unit. Typically a regular, repeating pattern of ionic bonds will exist.  In other words, a compound like NaCl will be connected to several other NaCl units.  A formula unit is the lowest whole-number ratio of ions in an ionic compound.

 Write the formula for both the cation and the anion.  Eliminate the (+) and (-) charges.  “Drop and drag” the numbers remaining as subscripts for the formula unit.  No charges will remain in the final formula.

Atoms Combining Ion FormulasFormulaName Sodium and Sulfur Barium and Oxygen Calcium and Phosphorus Potassium and Nitrogen Aluminum and Oxygen Lithium and Iodine

 Most ionic compounds are crystalline solids at room temperature. ◦ Arranged in regular, repeating, 3-D patterns ◦ Structure is related to coordination number (number of oppositely charged ions surrounding an ion.) ◦ See some examples here.here  Ionic compounds have high melting points.  Ionic compounds conduct an electric current when melted or dissolved in water.

 Metals are made up of closely packed cations rather than neutral atoms.  The valence electrons of metals can be modeled as a sea of electrons. ◦ Valence e- are mobile and can drift freely ◦ Metals are ductile and malleable ◦ Metals conduct electricity  Metal atoms are arranged in very compact and orderly patterns.  Check out this cool Nova Explanation of metals!this cool

 Alloys are mixtures composed of two or more elements, at least one of which is a metal.  Alloys are important because their properties are often superior to those of their component elements. ◦ Sterling silver: silver and copper ◦ Bronze: copper and tin ◦ Steel: iron, carbon, boron, chromium, manganese, molybdenum, nickel, tungsten, and vanadium Steel