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Chemical Formulas

Chemical Formulas. Chapter 7. H 2. H 2 O. NH 3. CH 4. A molecule is an aggregate of two or more atoms in a definite arrangement held together by chemical bonds. A diatomic molecule contains only two atoms. H 2 , N 2 , O 2 , Br 2 , HCl, CO.

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Chemical Formulas

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  1. Chemical Formulas Chapter 7

  2. H2 H2O NH3 CH4 A molecule is an aggregate of two or more atoms in a definite arrangement held together by chemical bonds A diatomic molecule contains only two atoms H2, N2, O2, Br2, HCl, CO A polyatomic molecule contains more than two atoms O3, H2O, NH3, CH4 2.5

  3. 11 protons 11 electrons 11 protons 10 electrons Na+ Na 17 protons 18 electrons 17 protons 17 electrons Cl- Cl An ion is an atom, or group of atoms, that has a net positive or negative charge. cation – ion with a positive charge If a neutral atom loses one or more electrons it becomes a cation. anion – ion with a negative charge If a neutral atom gains one or more electrons it becomes an anion. 2.5

  4. A monatomic ion contains only one atom Na+, Cl-, Ca2+, O2-, Al3+, N3- A polyatomic ion contains more than one atom OH-, CN-, NH4+, NO3- 2.5

  5. How many protons and electrons are in ? How many protons and electrons are in ? 27 78 3+ 2- Al Al 13 34 Do You Understand Ions? 13 protons, 10 (13 – 3) electrons 34 protons, 36 (34 + 2) electrons 2.5

  6. 2.5

  7. 2.6

  8. molecular empirical H2O A molecular formula shows the exact number of atoms of each element in the smallest unit of a substance An empirical formula shows the simplest whole-number ratio of the atoms in a substance H2O CH2O C6H12O6 O3 O N2H4 NH2 2.6

  9. ionic compounds consist of a combination of cations and an anions • the formula is always the same as the empirical formula • the sum of the charges on the cation(s) and anion(s) in each formula unit must equal zero The ionic compound NaCl 2.6

  10. 1 x +2 = +2 1 x +2 = +2 2 x +3 = +6 1 x -2 = -2 3 x -2 = -6 2 x -1 = -2 Formula of Ionic Compounds Al2O3 Al3+ O2- CaBr2 Ca2+ Br- Na2CO3 Na+ CO32- 2.6

  11. 2.6

  12. 2.7

  13. Chemical Nomenclature • Ionic Compounds • often a metal + nonmetal • anion (nonmetal), add “ide” to element name barium chloride BaCl2 potassium oxide K2O magnesium hydroxide Mg(OH)2 potassium nitrate KNO3 2.7

  14. Transition metal ionic compounds • indicate charge on metal with Roman numerals iron(II) chloride FeCl2 2 Cl- -2 so Fe is +2 FeCl3 3 Cl- -3 so Fe is +3 iron(III) chloride Cr2S3 3 S-2 -6 so Cr is +3 (6/2) chromium(III) sulfide 2.7

  15. Molecular compounds • nonmetals or nonmetals + metalloids • common names • H2O, NH3, CH4, C60 • element further left in periodic table is 1st • element closest to bottom of group is 1st • if more than one compound can be formed from the same elements, use prefixes to indicate number of each kind of atom • last element ends in ide 2.7

  16. TOXIC! Laughing Gas Molecular Compounds HI hydrogen iodide NF3 nitrogen trifluoride SO2 sulfur dioxide N2Cl4 dinitrogen tetrachloride NO2 nitrogen dioxide N2O dinitrogen monoxide 2.7

  17. 2.7

  18. 1S 32.07 amu 2O + 2 x 16.00 amu SO2 SO2 64.07 amu Molecular mass (or molecular weight) is the sum of the atomic masses (in amu) in a molecule. For any molecule molecular mass (amu) = molar mass (grams) 1 molecule SO2 = 64.07 amu 1 mole SO2 = 64.07 g SO2 3.3

  19. Do You Understand Molecular Mass? 8 mol H atoms 6.022 x 1023 H atoms 1 mol C3H8O x x x = 1 mol C3H8O 1 mol H atoms 60 g C3H8O How many H atoms are in 72.5 g of C3H8O ? 1 mol C3H8O = (3 x 12) + (8 x 1) + 16 = 60 g C3H8O 1 mol C3H8O molecules = 8 mol H atoms 1 mol H = 6.022 x 1023 atoms H 72.5 g C3H8O 5.82 x 1024 atoms H 3.3

  20. Heavy Heavy Light Light KE = 1/2 x m x v2 v = (2 x KE/m)1/2 F = q x v x B 3.4

  21. 2 x (12.01 g) 6 x (1.008 g) 1 x (16.00 g) n x molar mass of element %C = %H = %O = x 100% = 34.73% x 100% = 13.13% x 100% = 52.14% x 100% 46.07 g 46.07 g 46.07 g molar mass of compound C2H6O Percent composition of an element in a compound = n is the number of moles of the element in 1 mole of the compound 52.14% + 13.13% + 34.73% = 100.0% 3.5

  22. g CO2 g H2O mol CO2 mol H2O mol C mol H g H g C Combust 11.5 g ethanol Collect 22.0 g CO2 and 13.5 g H2O 6.0 g C = 0.5 mol C 1.5 g H = 1.5 mol H g of O = g of sample – (g of C + g of H) 4.0 g O = 0.25 mol O Empirical formula C0.5H1.5O0.25 Divide by smallest subscript (0.25) Empirical formula C2H6O 3.6

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