Chem 1120 Chapter 3 Week 5 Notes
Chem 1120 Chapter 3 Week 5 Notes Chem 1120-001
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This 7 page Class Notes was uploaded by Callie Simpson on Monday February 8, 2016. The Class Notes belongs to Chem 1120-001 at East Carolina University taught by James E. Collins in Winter 2016. Since its upload, it has received 119 views. For similar materials see Introduction to Chemistry for the Allied Health Sciences in Science at East Carolina University.
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Date Created: 02/08/16
Chapter 3 “Ionic Compounds” Compounds: Pure substances made of two or more elements that can’t be broken down into simpler substances by physical means. Compounds can be broken down into elements by chemical means. Compounds have definite proportions. Types: 1. Sodium Chloride –formed from a combination of a metal (Sodium) and a non-metal (Chlorine). 2. Carbon Dioxide –formed from a combination of two non-metals (Carbon and Oxygen). Sodium Chloride and Carbon Dioxide represent two different types of compounds found in nature. Although the bonding is different for these two types of compounds, they are formed for the same reasons. Ionic Compounds Molecular Compounds High melting solids Solids, liquids, or gases Dissolve in water Don’t dissolve in water Conduct electricity Aqueous solutions don’t conduct electricity Soluble in polar solvents and Made from nonmetals insoluble in nonpolar solvents Made from a combination of a Soluble in nonpolar solvent metal and a nonmetal and less soluble in polar solvents Molten aqueous solutions conduct electricity Submicroscopic scale compounds referred to as: Formula Units: Smallest whole number ratio of elements in ionic compounds. Molecules: Smallest entity for molecular compounds on atomic scale. Ions: Charged atoms or groups of atoms. Cations: Neutral atom that loses electrons and becomes positively charged. Metals tend to lose electrons to become cations. Anions: Neutral atoms that gain electrons and become negatively charged. Non-metals tend to gain electrons to become anions. *Ions formed only by adjusting number of electrons. The number of protons is not altered in a chemical reaction. Predicting the Charge of Ions: -The charge of many ions can be predicted based upon the position they are found on the periodic table. -Metals tend to lose electrons to acquire the same number of electrons as the preceding Noble gas. -Non-metals tend to gain electrons to acquire the same number of electrons as the Noble gas that follows them. - Your turn: How many protons (p+), neutrons (n), and electrons (e ) are present in a phosphide-31 isotope, 3115P ? Your turn: What ion would have 35 protons, 45 neutrons, and 36 electrons? Electron Dot Symbol for Ions: Cations are represented by removing electrons away from the neutral atom until the same number of electrons is arrived at as the next nearest Noble gas. For example, the electron dot symbol for a sodium cation, Na would be: Anions are represented by adding electrons to the neutral atom until the same number of electrons is arrived at as the next nearest Noble gas. 2- For example, the electron dot symbol for an oxide anion, O would be: Your turn: What is the electron dot symbol for a nitride, N ion? Polyatomic Ions: Polyatomic ions: groups of atoms that are charged. They are typically made up of a combination of non-metal atoms and most of them are anions. *Common Polyatomic Ions that you should learn. You should know their name, formula, and charge. Writing Formulas for Ionic Compounds: When writing the formula for a compound, there must be charge balance in the formula. The sum of the cationic charge must equal the sum of the anionic charge. For example, consider the compound formed from Al 3+ and O .- Two Al 3+ ions are required to balance the charge of 2- three O ions. Criss-Cross Method: Formulas for ionic compounds can be written by using the criss-cross method. In this method, the charge on the cation becomes the subscript of the anion in the formula and the charge on the anion becomes the subscript of the cation. The key is that the overall charge in the formula is zero. *Subscrips that have a common multiple should be reduced and subscripts that are one are omitted for clarity. For example: Mg O b2c2mes MgO *View polyatomic ions as one group and place parenthesis around them if the subscript is greater than one. For example: Mg (PO ) and not Mg PO 3 4 2 3 42 Your turn: What is the formula for the compound that combines silver(I) ions with oxide? Deducing the Charge of an Ion in an Ionic Compound: Some elements in a formula do not have an absolute charge that can be predicted. For example, the charge of most transition metals varies. In many cases, the charge of an element can be determined by simply reverse criss-cross. For example: The charge of each iron in Fe O is 2e 3 3+ *Metal charges are always positive and non-metal charges are always negative in an ionic compound. For example: What is the charge of the iron ion in FeO? If we use reverse criss-cross, we may falsely conclude that the charge for iron is 1+… Using Algebra, we assume that the sum of the charges of the ions in the compound equals zero. Your turn: What is the charge of Ni in the compound, Ni N ? 3 2 Your turn: What is the charge of Co in the compound, CoPO ? 4 Two Types of Ionic Compounds: When naming Ionic Compounds, we must first classify them into one of two groups: 1. Ionic Compounds with a metal that has a fixed charge. 2. Ionic Compounds with a metal in which its charge can vary from compound to compound. *Fixed charges of some common elements. Naming Binary Ionic Compounds: Binary ionic compounds: ionic compounds with two elements (a metal and a nonmetal) in its formula. If the metal has an absolute charge, then they are named by simply listing the metal followed by the nonmetal that has been modified with an “ide” ending. “Metal + modified Nonmetal” Example: NaCl is Sodium Chloride *List of some common modified nonmetals. Binary Ionic Compounds that consist of a Transition Metal: Since transition metals can have a variety of charges, a Roman numeral in parenthesis is included to indicate the charge of the metal. Examples: FeCl2is Iron (II) chloride and FeCl3is Iron (III) chloride CuO is Copper (I) oxide and Cu O 2s Copper (II) oxide SnI2is Tin (II) iodide and SnI4is Tin (IV) iodide Your turn: What is the systematic name for the compound, CaBr ? 2 What is the systematic name for the compound, PbCl ? 4 What is the formula for the compound, Cobalt (II) phosphate? Acids and Bases: Acid: a+substance that when dissolved in water produces hydrogen ions, H that combines with water (H O) t2 produce hydronium ion, H3O . Base: a substance that when dissolved in water produces hydroxide ions, OH . Naming Binary Acids: Binary acids: only have two elements in their formula. Binary acids are molecular compounds and can be named using the format for the pure substance: “Hydrogen + modified anion” Such as Hydrogen Chloride for HCl. In aqueous solutions of the acid, Hydrogen is modified to Hydro and the “ide” ending in chloride is changed to “ic acid”. And so HCL (aq) is Hydrochloric acid. Naming Oxo Acids: Oxoacids: are molecular compounds as well. They are acids that have a central non-metal atom covalently bonded to one or more oxygen atoms. At least one of the oxygen atoms is covalently bonded to hydrogen. An oxoacid takes the form: Oxoanions: are a family of polyatomic ions that have a central atom (usually a non-metal) covalently bonded to one or more oxygen atoms. Cl1 is perchlorate 4 Cl3 is chlorate Cl1 is chlorite 2 Cl1 is hypochlorite When naming aqueous solutions of oxoacids, the hydrogen is completely omitted from the name. Those oxoacids that contain an “ate” anion are modified by adding the suffix “ic acid” to replace ate. Examples: HNO is Nit3ic Acid H 2O i4 Sulfuric Acid Your turn: What is the systematic name of aqueous HI? What is the systematic name of aqueous H PO ? 3 4
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