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400 Chemistry Formulas and Naming of Ions and Compounds Information Conveyed by a Formula: 1. Which elements are present (chemical symbols) 2. The relative amount of each element present (subscripts which go with the element to their left) 3. Any net charge on the species (# followed by a + or – sign for ions, net charge on a compound is = 0 ) Note: Numbers outside parentheses multiply by all subscripts inside parentheses, numbers in front of formulas multiply by all subscripts in a formula. If no number is given, the quantity is one. Examples: H2O = hydrogen and oxygen combined so that for every 2 hydrogens, there is 1 oxygen Na2CO3 = 2 sodiums, 1 carbon, and 3 oxygens (or 2 sodium ions and 1 carbonate ion) H2SO4 = KI = (NH4)3PO4 = 3 nitrogens, 12 hydrogens, 1 phosphorous, 4 oxygens OR 3 ammonium ions (that’s the one in parentheses) and 1 phosphate ion CuSO4 ∙ 5 H2O = 1 copper, 1 sulfur, 9 oxygens, 10 hydrogens OR 1 copper ion and 1 sulfate ion and 5 waters BaCl2 ∙ 2 H2O = Recognizing Different Types of Formulas (we name things based on what type they are): -If it has a charge, it is an ion -If it starts with H, it is an acid -If it is made up of a metal and a nonmetal, it is an ionic compound -If it is made up of 2 nonmetals, it is a molecular compound -If it has a polyatomic ion in it, it is an ionic compound (more on that soon!) Examples: K+ HCl OH- CO NaCl BaSO4 NaOH PCl5 Mg2+ F- Ions Ion Charges and Oxidation Number Atom = smallest particle of an element that still retains the properties of that element Atoms have three subatomic particles: protons (positive charge), neutrons (neutral, no charge), electrons (negative charge) In a neutral atom, the number of protons is equal to the number of electrons (so a neutral atom has NO charge) Ion = a charged atom (number of protons and electrons is not equal) Cation = a positively charged ion (has more protons than electrons, has lost electrons) Anion = a negatively charged ion (has more electrons than protons, has gained electrons) Representative elements (A groups on Periodic Table) can be assigned a charge or oxidation number based on their location (group or family): 1+, 2+, 3+, 4+, 3-, 2-, 1-, 0 going across from left to right Transition elements (for reasons we’ll discuss later) can have multiple charges and there is not an obvious way to memorize them Some common cation charges can be memorized by using the following “chant” which groups elements with “unusual” charges with ones we know due to their group location: Pronounce it as it looks! HAgLiNaKCu HAgLiNaKCu CuBaCaFePbZnMg AlFeSbBiCr AlFeSbBiCr SiC, SiC, SiC (1+) (2+) (3+) (4+) How to Name Ions Cations: Just use the full element name, followed by “ion” or “cation” Ex: K+ potassium ion, Ca2+ calcium cation Anions: Use the element root and add “ide” to the end, followed by “ion” or “anion” Ex: Cl- chloride anion, O2- oxide anion, P3- phosphide ion Some cations (especially transition metals) can have more than one charge To be clear, we must indicate the charge that we mean Ex: Cu1+ is copper(I) or cuprous, Cu2+ is copper(II) or cupric So charge can be indicated in a name with a roman numeral in parentheses or by using the Latin/Greek root for the element with an –ic or –ous ending (-ic for the higher of the charges, -ous for the lower) Other common ones are: iron(II) and iron(III), mercury(I) and mercury(II), lead(II) and lead(IV), tin(II) and tin(IV), and various charges for chromium and manganese So far, we have been dealing with monatomic ions Monatomic ion = ion consisting of only one element (and atom) Polyatomic ion = group of atoms held together with a net charge (very important in many of the compounds we will use!) Polyatomic Ions Essential for naming and writing formulas for compounds! Some must be memorized, some can be derived from the ones you memorize! Here’s the list- memorize these (the names and formulas with charges)… and then we will have rules to help you derive any others you need! Cations NH4+ ammonium Hg22+ mercury(I) Anions ClO3- chlorate NO3- nitrate CO32- carbonate SO42- sulfate PO43- phosphate CN- cyanide CNO- cyanate OH- hydroxide C2H3O2- acetate C2O42oxalate MnO4 permanganate CrO42chromate Cr2O72dichromate How to Derive Other Names 1. If the formula is similar to one on the list but has 1 less oxygen, change the ending to “ite” 2. If the formula is similar to an “ite” polyatomic ion but has 1 less oxygen than that one, add the prefix “hypo” and keep the “ite” ending 3. If the formula is similar to one on the list but has 1 more oxygen, keep the usual ending but add the prefix “per” 4. If 1 hydrogen appears in the formula, add “hydrogen” or “monohydrogen” to the name; if 2 hydrogens appear in the formula, add “dihydrogen” to the name 5. If an oxygen in a formula is replaced with a sulfur, add “thio” as a prefix 6. Don’t forget to use the Periodic Table… elements in the same group behave similarly and are named similarly Examples…. BrOSiO32AsO43CNSO22HCO3HAsO42H2AsO4SO32S2O32Answers: hypobromite, silicate, arsenate, thiocyanate, peroxide, hydrogen carbonate, hydrogen arsenate, dihydrogen arsenate, sulfite, thiosulfate Naming From Formulas Molecular (covalent) – use prefixes to indicate the number you have of each element (but never use mono for the first one listed), -ide ending o 1 = mono o 2 = di o 3 = tri o 4 = tetra o 5 = penta o 6 = hexa o 7 = hepta o 8 = octa o 9 = nona o 10 = deca Ionic – name the cation first, followed by the anion, -ide ending if monatomic ions… -ide, -ite, or –ate for polyatomic ions o If it contains a cation that can have more than one charge, use a roman numeral to show the charge Hydrates - First, name the compound. Then add a prefix to indicate the number of waters. Then add the word “hydrate” to the end. Ex: CuSO4 ∙ 5 H2O is copper(II) sulfate pentahydrate Elements that are diatomic molecules in nature: Seven elements (hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine, iodine) appear in nature as diatomic molecules. For these elements, even though we see the formula written with 2, we simply identify them by using the element name. Ex: O2 is oxygen, H2 is hydrogen To remember these elements, use one of the following mnemonic devices: “Horses Need Oats For Clear Brown “I”s” Or “I Never Fish On His Clean Brook” Or the Billy J rule (I don’t like this one but silly students seem to!) “BrIFClOHN” Acids: o Binary (H plus one element): hydro- root of element –ic acid o Converting Polyatomic Ion Names Into Acid Names: Use the following mnemonic device to help… “I ATE something ICky, I mITE get nauseOUS” So, polyatomic ions with names ending in “ate” will produce acids with names ending in “ic”, and polyatomic ions with names ending in “ite” will produce acids with names ending in “ous” Writing Formulas from Names To write a formula for an ionic compound or acid: 1. Using the name, write down the formulas and the charges for the ions involved (if an acid make sure to determine which ions are present first by invoking the naming rules) 2. Use the criss-cross rule to determine the subscripts (see demo on board) 3. Reduce the subscripts if necessary (they should be the lowest whole numbers possible) 4. To use subscripts with polyatomic ions, put parentheses around the polyatomic ion with the subscript on the outside 5. Once you have a formula and you believe it is correct, check to make sure that the net charge on the compound is equal to ZERO To write a formula for a molecular compound: 1. Use the prefixes in the name of the compound to determine how many of each element are present 2. Write a formula where you express those prefixes as subscripts