Ion: a single charged atom or a small group of atoms with a charge. negative charge (anion) positive charge (cation) Element Symbol cesium barium arsenic iodine Zinc Phosphorous sulfur Electron configuration Electron dot structure Electrons lost or gained? Ion symbol Ion name Element Symbol Electron configuration Electron dot structure Electrons lost or gained? Ion symbol Ion name Cs [Xe]6s1 Cs. 1 lost Cs+ cesium cesium barium arsenic iodine Zinc Phosphorous sulfur Ionic Compounds 1. Ionic compounds are formed between oppositely charged ions, usually a metal and one or more non-metals because they have a large difference in their electronegativity. 2. Binary ionic compounds are composed of two single atom ions. Naming Binary ionic compounds are named by removing the end of the name from the nonmetal and adding -ide. Examples: Sodium & chlorine form Sodium Chloride. Magnesium & oxygen form Magnesium Oxide. Calcium & sulfur form Calcium Sulfide. Writing Formulas for ionic compounds 1. Find charges on each ion. (Look on the periodic table or ion table.) 2. The positive and negative charges must exactly balance each other in order to form a neutral compound. Ex: Sodium forms a +1 charged ion: Sulfur forms a -2 charged ion: Na+1 S-2 The formula for Sodium Sulfide is: Na2S Calcium Fluoride = Potassium Chloride = Lithium Oxide = Aluminum Sulfide = Calcium Potassium Fluoride = CaF2 Chloride = KCl Lithium Oxide = LiO Aluminum Sulfide = Al2S3 Polyatomic Ionic Compounds Sometimes a group of atoms can have a charge. This is called a polyatomic ion. Some common poly atomic ions are: nitrate NO3-1 sulfate SO4-2 carbonate CO3-2 bicarbonate (or hydrogen carbonate) hydroxide OH-1 HCO3-1 Notice that the names of most of these ions end in -ate. When you see a name ending in -ate it probably implies that it is a polyatomic ionic compound. The groups of atoms can be thought of as a single entity with a charge, just like a single atom can have a charge. Example: Sodium Nitrate needs one +1 sodium ion to neutralize one -1 nitrate ion, so the formula is NaNO3 If you need more than one polyatomic ion, then you put parenthesis around it in the formula. Example: Calcium Nitrate needs one +2 calcium ion to neutralize two -1 nitrate ions, so the formula is Ca(NO3)2 Sodium Sulfate = Zinc Phosphate = Barium Hydroxide = Ammonium Sulfate = Sodium Sulfate = Zinc Phosphate = Na2SO4 Zn3(PO4)2 Barium Hydroxide = Ammonium Sulfate = Ba(OH)2 (NH4)2(SO4) Ions with multiple charges Some atoms (typically transition elements) can commonly form 2 or 3 different charges. Copper, for example, usually forms +1 or +2 charged ions. We specify the ions by adding a Roman numeral to the name: Cu+1 is Copper(I) and Cu+2 is Copper(II). So. . . . Copper(II)Oxide is CuO and Copper(I)Oxide is Cu2O. Properties of ionic compounds: 1 2 3 o High melting points (> than 150 C). Ionic solids conduct electricity when melted or dissolved in water. Ionic solids are hard and brittle. Ionic solids have . . . . . . . HIGH melting points because ionic bonds are very strong. Electrostatic forces hold positive cations and negative anions together in a strong crystal lattice arrangement. Ionic solids are . . . . . . . POOR conductors because electrical and heat conductivity depends on electrons being able to move freely. Electric charge is "locked" in the lattice positions of the ions in ionic solids. This means there is poor mobility of charges and poor conductivity of electricity and heat. BUT. . . . . . Ionic solids are . . . . . . . good conductors when melted. When ionic solids melt, ions are mobile and can carry electrical charge through the liquid. This is why a molten ionic substance conducts electricity, but a solid ionic substance doesn't. Ionic solids are . . . . . . . good conductors when dissolved in water. . The solvent pulls the ions out of the solid and breaks the forces holding the crystal together. The solvent isolates the ions in an envelope of solvent particles. The ions are free to move and carry electric charge through the solution. Ionic solids are . . . . . . . brittle and hard because the electrostatic attractions in the solid hold the ions in definite positions. The attractions must be overcome to move the ions. When the ions in the solid are shifted by some very strong force, the positions of ions shift so that like charged ions are close together. This results in strong repulsions and the like charged ions move apart. This causes the solid to shatter and not simply deform like a metal.