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Chemical Formulas

Chemical Formulas. Chemical formulas always tell us two things. Type of elements present. Number of atoms. The subscripts after the elements indicate the number of atoms. Examples. MgBr 2. 1 Mg for every 2 bromines. 2 aluminums for every 3 oxygens. Al 2 O 3. Ca(OH) 2.

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Chemical Formulas

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  1. Chemical Formulas Chemical formulas always tell us two things Type of elements present Number of atoms The subscripts after the elements indicate the number of atoms Examples MgBr2 1 Mg for every 2 bromines 2 aluminums for every 3 oxygens Al2O3 Ca(OH)2 1 calcium , 2 hydrogens and 2 oxygens 2 sets of OH Example - How many sulfur atoms are present in Pb(SO4)2? 2 4 x 2 = 8 How many oxygen atoms are present?

  2. A. Types of Chemical Equations 1. Empirical Formula Tells us the simplest ratio of atoms Typically used in ionic compounds All atoms are connected to each other Examples NaCl One Na for each Cl CH2O One carbon for every 2 hydrogens for every one oxygen Does not tell us how many atoms are in a molecule 2. Molecular Formula Tells us how many atoms are bonded in a molecule Not always the simplest ratio C2H6 2 carbons and 6 hydrogens are all bonded into one group Sometimes the empirical formula and the molecular formula are the same CO2 H2O

  3. Which of the following are empirical formulas? A. H2O2 B. CO C. P2O4 D. Al2O3 What is the empirical formula of the following? A. C6H12O6 b. Hg2O4 c. PbSO4 PbSO4 CH2O HgO2 B. Writing Chemical Formulas When Ba is combined with Cl, is the formula BaCl? Or Ba2Cl? Or ClBa? Or Cl2Ba? Chemical formulas are based on OXIDATION NUMBERS Oxidation numbers - Indicate the number of electrons lost or gained in a bond

  4. Found in the upper right hand corner of the Periodic Table Oxidation number Positive oxidation number Atom loses partial or total control of electrons Negative oxidation number Atom gains partial or total control of electrons Rules for Writing Formulas 1. The element or ion with the positive oxidation state is written first Write in the oxidation states, then write out who comes first. Mg Br +2 -1 -1 +2 Ca Cl -2 O +? Cu +1 -2 S Li

  5. -1 Cl 2. The oxidation states of all elements in a compound must add up to zero For every electron lost, it must be gained by another atom Example -1 +2 Cl Ca CaCl2 Loses control of 2 e- Gains control of 1e- 2 e- Add one more Cl-1 to get to zero +1 H2O -2 H O Li S +1 -2 Li2S 3. Polyatomic ions are treated as one element +2 -2 Ca SO4 Na PO4 CaSO4 +1 -3 Na3PO4

  6. 4. If a polyatomic ion is used more than once, put parentheses around it +2 -1 Ca(OH)2 Ca OH NH4 SO3 +1 -2 (NH4)2SO3 Practice Li+1 O-2 Li2O Lithium oxide Magnesium iodide potassium phosphate ammonium nitrate aluminum oxide calcium phosphate Mg+2 I- MgI2 PO4-3 K3PO4 K+1 NO3- NH4NO3 NH4+ Al+3 O-2 Al2O3 Ca+2 PO4-3 Ca3(PO4)2

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