chem chapter 7
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Chapter 9 Chemical Names and Formulas 9. Chemistry also uses recipes or formulas, but without any secrets. Binary Ionic CompoundsBefore the science of chemistry developed, compounds were often named to describe some property of the substance or its source. For example, a common name for potassium carbonate K2CO3 is potash because the compound was obtained by boiling wood ashes in iron pots.
NaHCO3 is called baking soda because it is used in baking to make baked goods rise. Binary Ionic CompoundsThe red substance deposited in this rock is commonly called cinnabar. Unfortunately, names like cinnabar do not tell you anything about the chemical composition of the compound.
Binary Ionic CompoundsThe French chemist Antoine-Laurent Lavoisier — determined the composition of many compounds, and found that it was becoming impossible to memorize all the unrelated names of the compounds.
He worked with other chemists to develop a systematic method for naming chemical compounds. Their work is the basis for the system we use today.
Binary Ionic CompoundsA binary compound is composed of two elements. Binary compounds can be ionic compounds or molecular compounds. If you know the name of a binary ionic compound, you can write the formula. Writing Formulas for Binary Ionic Compounds. Binary Ionic CompoundsTo write the formula of a binary ionic compound, first write the symbol of the cation and then the anion.
Then add subscripts as needed to balance the charges. The positive charge of the cation must balance the negative charge of the anion so that the net ionic charge of the formula is zero. The ions combine in a 1: Binary Ionic CompoundsThe figure at left shows one step in the process of making steel from iron ore.
Hematite, a common ore of iron, contains iron III oxide. What is the formula for this compound? The balanced formula is Fe2O3. Binary Ionic CompoundsAnother approach to writing a balanced formula for a compound is to use the crisscross method. In this method, the numerical value of the charge of each ion is crossed over and becomes the subscript for the other ion. Binary Ionic CompoundsNotice that the signs of the charges are dropped.
The formula is correct because the overall charge of the formula is zero, and the subscripts are expressed in the lowest whole-number ratio. The correct formula for calcium sulfide is CaS. Binary ionic compounds are composed of a monatomic cation and a monatomic anion. The symbol for the cation appears first in the formula for the compound. The ionic charges in an ionic compound must balance, and the ions must be combined in the lowest whole-number ratio.
Write the symbol and charge for each ion in the compound—the cation first, then the anion. Balance the formula using appropriate subscripts. Make sure that the formula expresses the lowest whole-number ratio of ions.
Check that the charges of the two ions add up to zero. Binary Ionic CompoundsIf you know the formula for a binary ionic compound, you can write its name. First, you must verify that the compound is composed of a monatomic metallic cation and a monatomic nonmetallic anion.
Naming Binary Ionic Compounds. Binary Ionic Compounds To name any binary ionic compound, place the cation name first, followed by the anion name. Both cesium and oxygen are Group A elements that have only one charge. The name of Cs2O is cesium oxide.
The name of NaBr is sodium bromide, and the name of SrF2 is strontium fluoride. The name copper oxide is incomplete. Recall that copper commonly forms two cations: The formula indicates that the copper cation and oxide anion combine in a 1: The oxide anion always has a 2— charge.
Binary Ionic CompoundsIf the metallic element in a binary ionic compound has more than one common ionic charge, a Roman numeral must be included in the cation name. Binary Ionic CompoundsLesson 9. The charges of monatomic ions can be determined from the periodic table. The first element in the formula is named first, using the full element name. The second element is named as if it were an anion.
Prefixes are used to denote the numbers of atoms present. The prefix mono- is never used for naming the first element. Chemical names for the ionic compounds are given according to rules.
The positive ion is always the first part of the name. The negative ion is always the second part of the name. This balance of charge is used to determine the smallest whole number ratio of positive to negative ions. To distinguish between different ions for multivalent metals, Roman numerals are added to their name.
Writing formulas for multivalent ionic compoundsTransition metals have the ability to form more than one cation Therefore, a roman numeral is placed in the name to signify the charge on the cation Example: Writing formulas for mulitvalent ionic compoundsWrite formulas for the following: You will have to deduce the roman numeral based on the formula. Example Name CoI2 Answer - Cobalt II Iodide Naming compounds with multivalent metalsDeducing the roman numeral Multiply the charge on the anion by the number of anions and then divide by the number of cations to get the roman numeral.
Rules for Naming Ionic Compounds. Writing formulas for multivalent ionic compounds. Naming compounds with functional groups. Naming and Writing Formulas for Ionic Compounds. Naming and Writing Formulas for Molecular Compounds. Naming Polyatomic Ionic Compounds.