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Introduction to Chemical Formulas and Stoichiometry

Learn about chemical formulas, ions, and ionic compounds, as well as naming and determining formulas of compounds. Understand the concept of stoichiometry and composition.

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Introduction to Chemical Formulas and Stoichiometry

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  1. Chapter 2 Chemical Formulas and Composition Stoichiometry

  2. Chapter Goals • Chemical Formulas • Ions and Ionic Compounds • Names and Formulas of Some Ionic Compounds • Atomic Weights • The Mole • Formula Weights, Molecular Weights, and Moles • Percent Composition and Formulas of Compounds • Derivation of Formulas from Elemental Composition • Determination of Molecular Formulas • Some Other Interpretations of Chemical Formulas • Purity of Samples

  3. Chemical Formulas • Chemical formula shows the chemical composition of the substance. • ratio of the elements present in the molecule or compound • He, Au, Na – monatomic elements • O2, H2, Cl2 – diatomic elements • O3, P4, S8 - more complex elements • H2O, C12H22O11 – compoundsSubstance consists of two or more elements

  4. Chemical Formulas Compound1 Molecule Contains HCl 1 H atom & 1 Cl atom H2O 2 H atoms & 1 O atom NH3 1 N atom & 3 H atoms C3H8 3 C atoms & 8 H atoms

  5. Ions and Ionic Compounds • Ions are atoms or groups of atoms that possess an electric charge. • Two basic types of ions: • Positive ions or cations • one or more electrons less than neutral • Na+, Ca2+, Al3+ • NH4+ - polyatomic cation • Negative ions or anions • one or more electrons more than neutral • F-, O2-, N3- • SO42-, PO43- - polyatomic anions

  6. Ions and Ionic Compounds • Sodium chloride • table salt is an ionic compound

  7. Systematic Naming • There are too many compounds to remember the names of them all. • Compound is made of two or more elements. • Name should tell us how many and what type of atoms.

  8. Charges on ions • For most of Group A elements, location on the Periodic Table can tell what kind of ion they form • Elements in the same group have similar properties. • Including the charge when they are ions.

  9. Charge in groups 1A, 2A and 3A is the group number 1+ 2+ 3+ 3- 2- 1-

  10. Naming Monatomic Ions • 1. Monatomic cations are • Identified by the element’s name • 2. Monatomic anions • Drop the ending of the element name • Add an “–ide” ending

  11. Name these • Na1+ Sodium ion • Ca2+ Calcium ion • Al3+ Aluminum ion • Li1+ Lithium ion

  12. Write Formulas for these K1+ • Potassium ion Mg2+ • Magnesium ion Cu2+ • Copper(II) ion Cr6+ • Chromium(VI) ion Ba2+ • Barium ion Hg2+ • Mercury(II) ion

  13. Name these • Cl1- Chloride ion • N3- Nitride ion • Br1- Bromide ion Oxide ion • O2- Gallium ion • Ga3+

  14. Write these • Sulfide ion S2- • Iodide ion I1- • Phosphide ion P3- • Strontium ion Sr2+

  15. Binary Ionic Compounds • Binary Compounds • Compounds composed of two different elements • Binary ionic cmpd, total # of positive and negative charges must equal

  16. Writing Formulas for Binary Ionic Compounds • Write the symbols for the ions side by side. ALWAYS write the cation first! Al3+ O2- • Cross over the charges by using the absolute value of each ion’s charge as the subscript for the other ion Al23+O32- • Check that the subscripts are in smallest whole number ratio Al2O3

  17. Naming Binary Ionic Compounds Al2O3 • 1. Name the cation(don’t change) Aluminum • 2. Name the anion (drop add-ide) Oxide Aluminum Oxide

  18. The Stock System of Nomenclature • Most transition metals can have more than one type of charge. • Indicate the charge with Roman numerals in parenthesis. • Fe2+Iron(II) • Fe3+ Iron(III) • Roman numerals are never used: • For anions • For metals that form only one ion Co2+ Cobalt(II) ion CuCl2 Copper(II) chloride

  19. Naming ions Cont….. • A few, like silver, zinc and cadmium only form one kind of ion • Don’t get roman numerals • Ag+ silver ion • Zn2+ zinc ion • Cd2+ cadmium ion

  20. Compounds Containing Polyatomic Ions • Naming a series of similar polyatomic ions • NO2- NO3- • Nitrite Nitrate • Most common ion is given –ate ending, ion with one less oxygen -ite • Naming compounds containing polyatomic ions • Same as for monatomic ions

  21. Naming Binary Molecular Compounds A. Binary Molecular Compounds • 1. Covalently bonded molecules containing only two elements, both nonmetals B. Naming • 1. Least electronegative element is named first • Measure of the ability of an atom in chemical compound to attract e- • Tends to increase across periods decrease or remain the same down • 2. First element gets a prefix if there is more than 1 atom of that element • 3. Second element ALWAYS gets a prefix, and an “-ide” ending • Examples: N2O3= dinitrogen trioxide • CO = carbon monoxide, not monocarbon monoxide

  22. Names and Formulas of Some Ionic Compounds • Table 2-1 gives names of several molecular compounds. • You must know all of the molecular compounds from Table 2-2. • Some examples are: • H2SO4 - sulfuric acid • FeBr2 - iron(II) bromide • C2H5OH - ethanol

  23. Names and Formulas of Some Ionic Compounds • Table 2-2 displays the formulas, charges, and names of some common ions • You must know the names, formulas, and charges of the common ions in table 2-3. • Some examples are: • Anions - Cl1-, OH1-, SO42-, PO43- • Cations - Na1+, NH41+, Ca2+, Al3+

  24. Acid Nomenclature

  25. Acid Nomenclature C. Johannesson

  26. Acid Nomenclature • HBr • H2CO3 • H2SO3 hydrobromic acid 2 elements, -ide  carbonic acid 3 elements, -ate  sulfurous acid 3 elements, -ite

  27. Acid Nomenclature • hydrofluoric acid • sulfuric acid • nitrous acid 2 elements  H+ F-  HF 3 elements, -ic  H+ SO42-  H2SO4  H+ NO2-  HNO2 3 elements, -ous

  28. Names and Formulas of Some Ionic Compounds You do it! • What is the formula of nitric acid? • HNO3 • What is the formula of sulfur trioxide? • SO3 • What is the name of FeBr3? • iron(III) bromide

  29. Names and Formulas of Some Ionic Compounds You do it! • What is the name of K2SO3? • potassium sulfite • What is charge on sulfite ion? • SO32- is sulfite ion • What is the formula of ammonium sulfide? • (NH4)2S

  30. Names and Formulas of Some Ionic Compounds You do it! • What is the charge on ammonium ion? • NH41+ • What is the formula of aluminum sulfate? • Al2(SO4)3 • What are the charges on both ions? • Al3+ and SO42-

  31. Atomic Weights • Weighted average of the masses of the constituent isotopes of an element. • Tells us the atomic masses of every known element. • Lower number on periodic table.

  32. The Mole • A number of atoms, ions, or molecules that is large enough to see and handle. • A mole = number of things • Just like a dozen = 12 things • One mole = 6.022 x 1023 things • Avogadro’s number = 6.022 x 1023 • Symbol for Avogadro’s number is NA.

  33. HOW LARGE IS IT??? • 1 mole of pennies would cover the Earth 1/4 mile deep! • 1 mole of hockey pucks would equal the mass of the moon! • 1 mole of basketballs would fill a bag the size of the earth!

  34. The Mole Example 2-1: Calculate the mass of a single Mg atom, in grams, to 3 significant figures.

  35. The Mole Example 2-1: Calculate the mass of a single Mg atom, in grams, to 3 significant figures.

  36. The Mole Example 2-2: Calculate the number of atoms in one-millionth of a gram of Mg to 3 significant figures.

  37. The Mole Example 2-2: Calculate the number of atoms in one-millionth of a gram of Mg to 3 significant figures.

  38. The Mole Example 2-3: How many atoms are contained in 1.67 moles of Mg?

  39. The Mole Example 2-3. How many atoms are contained in 1.67 moles of Mg?

  40. The Mole Example 2-4: How many moles of Mg atoms are present in 73.4 g of Mg? You do it!

  41. The Mole Example 2-4: How many moles of Mg atoms are present in 73.4 g of Mg? IT IS IMPERATIVE THAT YOU KNOW HOW TO DO THESE PROBLEMS

  42. Formula Weights, Molecular Weights, and Moles • How do we calculate the formula weight of a compound? • sum the atomic weight of each atom The formula weight of propane, C3H8, is:

  43. Formula Weights, Molecular Weights, and Moles The formula weight of calcium nitrate, Ca(NO3)2, is: You do it!

  44. Formula Weights, Molecular Weights, and Moles

  45. Formula Weights, Molecular Weights, and Moles • One Mole of Contains • Cl2 or 70.90g 6.022 x 1023 Cl2 molecules 2(6.022 x 1023 ) Cl atoms

  46. Formula Weights, Molecular Weights, and Moles Example 2-5: Calculate the number of C3H8 molecules in 74.6 g of propane.

  47. Formula Weights, Molecular Weights, and Moles Example 2-5: Calculate the number of C3H8 molecules in 74.6 g of propane.

  48. Formula Weights, Molecular Weights, and Moles Example 2-6: What is the mass of 10.0 billion propane molecules? You do it!

  49. Formula Weights, Molecular Weights, and Moles Example 2-6. What is the mass of 10.0 billion propane molecules?

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