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Finding the Mass of Compounds Notes What are compounds? - Compounds are composed of 2 or more atoms bonded together forming a single unit Examples… - H2O, NH3, Br2, C6H12O6, and NaCl There are two main types of compounds To summarize: 1. Molecules: compounds composed of atoms connected by covalent bonds (sharing of electrons, usually between nonmetals) 2. Ionic Compounds (Formula Units): compounds composed of atoms connected by ionic bonds (giving up and accepting electrons, occurs between metals and nonmetals). Compounds Molecules Covalent bonds Chemical Formulas: Ionic Compounds Ionic Bonds - designed to represent the number and types of elements in a compound. Important numbers in chemical formulas: 1. Subscript Example - indicates the number of atoms of each type of elements in a compound H2O and CH4 Subscripts written in the lower right-hand corner of the element it represents - If only one atom of an element is in the compound, no subscript is written in the absence of a subscript, assume the number is one. Ca(NO3)2 - The () surround the NO3 portion of the compound; the subscript 2 is in the lower right hand corner of the (). The parentheses and subscript indicate that that portion of the compound appears twice in the formula NO3-1–-Ca 2+– NO3-1 -In other words, there are two sets of NO3 molecules in this compound. To determine the number of N and O, multiply your subscripts (N 1 x 2 = 2 N, O 3 x 2 = 6 O) - Another example What do the parentheses indicate in this chemical formula? 2. Coefficient Example - indicates number of compounds or moles present in a chemical reaction N2 + 3 H2 2 NH3 Coefficients - written in normal script to the left of the compound it represents - If no coefficient is present assume the number is one. - Coefficients are used to group like molecules in a chemical reaction making it easier to read. Without Coefficients N2 + H2 + H2 + H2 NH3 + NH3 With Coefficients N2 + 3 H2 2 NH3 How to find the mass of a compound – 4 Steps to finding the 1. Take inventory of the elements in the mass of a compound compound (write out the element’s symbol and the number of atoms of that element) 2. Find the average atomic mass of each element using your periodic table 3. Multiply the number of each element by its atomic mass 4. Add up all the masses. Examples Find the mass of C6H12O6: Step 1: C = 6 H = 12 O= 6 Step 2: C = 6 12.01 H = 12 1.01 O= 6 16.00 Step 3: C = 6 x 12.01 = 72.06 H = 12 x 1.01 = 12.12 O = 6 x 16.00 = 96.00 Step 4: C = 6 x 12.01 = 72.06 H = 12 x 1.01 = 12.12 O = 6 x 16.00 = +96.00 180.18 Mass of C6H12O6 is 180.18 amu Final example Find the mass of Sr(CO3)2 Step 1: Sr = 1 C=2 O= 6 Step 2: Sr = 1 87.62 C=2 12.01 O= 6 16.00 Step 3: Sr = 1 x 87.62 = 87.62 C = 2 x 12.01 = 24.02 O = 6 x 16.00 = 96.00 Step 4: Sr = 1 x 87.62 = 87.62 C = 2 x 12.01 = 24.02 O = 6 x 16.00 = +96.00 207.64 Mass of Sr(CO3)2 is 207.64 amu