Chapter 3  Atoms: the Building Blocks of Matter
<ul><li>The parts that make up an atom are called  subatomic particles . </li></ul><ul><ul><li>1) Protons (p + ) positivel...
<ul><li>Q- How are atoms of different elements distinguished from  </li></ul><ul><li>one another? In other words, how do w...
Atomic Structure Here are the basics; you need to know these. 1 H 1.0076 Hydrogen Atomic Number ( Z ) : the number of  pro...
Lets practice! Find the missing information? 8 15.999 amu O 2 2 He 39.948 amu 18 Ar Neutrons Electrons Protons Atomic Mass...
The Famous Gold Foil Experiment <ul><li>This showed us that the atom is made of mostly </li></ul><ul><li>empty space . </l...
Isotopes Atoms of the same element with different number of  neutrons <ul><li>Because they have the same number of protons...
Mass Numbers of Hydrogen Isotopes <ul><li>What would the masses be? </li></ul>
The Mole: A Measurement of Matter <ul><li>At the end of this section, you should </li></ul><ul><li>be able to: </li></ul><...
The Mole  (aka Avagadro’s Number) : 6.02 x 10 23
The Mole and Avogadro’s Number <ul><li>SI unit that measures the amount of substance </li></ul><ul><li>1 mole = 6.02 x 10 ...
But Why the Mole? <ul><li>Just as 12 = 1 dozen, or 63,360 inches = 1 mile, </li></ul><ul><li>the mole allows us to count m...
Examples: 6.02 x 10 23 Ca 2+ Ion Calcium ion 6.02 x 10 23 H 2 O Molecule Water 6.02 x 10 23 N Atom Atomic nitrogen Represe...
Solve Representative Particles in 1.00 mol Formula Unit Representative  Particle Substance Molecule C Carbon Molecule C 12...
Answers <ul><li>Nitrogen gas-molecule-N 2 </li></ul><ul><li>Calcium fluoride-formula unit-CaF 2 </li></ul><ul><li>Sucrose-...
How many atoms are in a mole? <ul><li>Determined from the chemical formula </li></ul><ul><li>List the elements and count t...
Solve: How many atoms are in a mole of <ul><li>1.  Carbon monoxide – CO </li></ul><ul><li>2.  Glucose – C 6 H 12 O 6 </li>...
How many moles of magnesium is 1.25 x 10 23  atoms of magnesium? <ul><li>Refer to page 174 in text </li></ul><ul><li>Divid...
Objectives <ul><li>Use the molar mass to convert between mass and moles of a substance </li></ul><ul><li>Use the mole to c...
Molar mass <ul><li>Mass (in grams) of one mole of a substance </li></ul><ul><li>Broad term (can be substituted) for gram a...
Molar Mass <ul><li>Gram atomic mass (gam) – atomic mass of an element taken from the periodic table </li></ul><ul><li>Gram...
Calculating the Molar Mass of Compounds (Molecular and Ionic) <ul><li>1.  List the elements </li></ul><ul><li>2.  Count th...
What is the molar mass (gfm) of ammonium carbonate (NH 4 ) 2 CO 3 ? <ul><li>N  2 x 14.0 g =  28.0 g </li></ul><ul><li>H  8...
Practice Problems <ul><li>1.  How many grams are in 9.45 mol  </li></ul><ul><li>of dinitrogen trioxide (N 2 O 3 ) ? </li><...
Answers <ul><li>1.  718 g N 2 O 3  (one mole is 76.0g) </li></ul><ul><li>2.  0.578 mol Fe 2 O 3  (one mole is 159.6 g) </l...
Volume of a Mole of Gas <ul><li>Varies with a change in temperature or a change in pressure </li></ul><ul><li>At STP, 1 mo...
<ul><li>22.4 L of any gas at STP contains 6.02 x 10 23  representative particles of that gas </li></ul><ul><li>One mole of...
Objectives <ul><li>Define the terms </li></ul><ul><li>Calculate the percent composition of a substance from its chemical f...
Terms to Know <ul><li>Percent composition – relative amounts of each element in a compound </li></ul><ul><li>Empirical for...
An 8.20 g piece of magnesium combines completely with 5.40 g of oxygen to form a compound.  What is the percent compositio...
Answer <ul><li>The total mass is 8.20 g + 5.40 g = 13.60 g </li></ul><ul><li>Divide 8.2 g by 13.6 g and then multiply by 1...
Calculate the percent composition of propane (C 3 H 8 ) <ul><li>1.  List the elements </li></ul><ul><li>2.  Count the atom...
Answer <ul><li>Total molar mass = 44.0 g/mol </li></ul><ul><li>36.0 g C = 81.8% </li></ul><ul><li>8.0 g H = 18.2% </li></ul>
Calculate the mass of carbon in 52.0 g of propane (C 3 H 8 ) <ul><li>Calculate the percent composition using the formula (...
<ul><li>1) Find the percent composition of  </li></ul><ul><li>Aluminum Oxide (Al 3 O 2 ) </li></ul><ul><li>2) How much of ...
Calculating Empirical Formulas <ul><li>Microscopic – atoms </li></ul><ul><li>Macroscopic – moles of atoms </li></ul><ul><l...
Empirical Formulas <ul><li>The first step is to find the mole-to-mole ratio of the elements in the compound </li></ul><ul>...
What is the empirical formula of a compound that is 25.9% nitrogen and 74.1% oxygen? <ul><li>1.  Assume 100 g of the compo...
<ul><li>4. 1.85/1.85 = 1 mol N </li></ul><ul><li>4.63/1.85 = 2.5 mol O </li></ul><ul><li>5.  Multiply by a number that con...
Determine the Empirical Formulas <ul><li>1.  H 2 O 2   </li></ul><ul><li>2.  CO 2  </li></ul><ul><li>3.  N 2 H 4 </li></ul...
Answers <ul><li>Compound  Empirical Formula </li></ul><ul><li>1.  H 2 O 2   HO </li></ul><ul><li>2.  CO 2  CO 2  </li></ul...
Calculating Molecular Formulas <ul><li>The molar mass of a compound is a simple whole-number multiple of the molar mass of...
Calculate the molecular formula of the compound whose molar mass is 60.0 g and empirical formula is CH 4 N. <ul><li>1.  Us...
Answer <ul><li>Molar mass (efm) is 30.0 g </li></ul><ul><li>60.0 g divided by 30.0 g = 2 </li></ul><ul><li>Answer: C 2 H 8...
Practice Problems <ul><li>1) What is the empirical formula of a compounds that is 25.9% nitrogen and 74.1% oxygen? </li></...
Practice Problems <ul><li>4) What is the molecular formula for each compound: </li></ul><ul><li>a) CH 2 O, 90 g/mol </li><...
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Chemistry Chapter 3

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Chemistry Chapter 3

  1. 1. Chapter 3 Atoms: the Building Blocks of Matter
  2. 2. <ul><li>The parts that make up an atom are called subatomic particles . </li></ul><ul><ul><li>1) Protons (p + ) positively charged particle </li></ul></ul><ul><ul><li>2) Neutron (n o ) neutral particle (uncharged) </li></ul></ul><ul><ul><li>3) Electrons (e - ) negatively charged particle </li></ul></ul><ul><li>Neutrons and Protons are located in the nucleus of an atom. </li></ul><ul><li>Electrons orbit around the nucleus. </li></ul>
  3. 3. <ul><li>Q- How are atoms of different elements distinguished from </li></ul><ul><li>one another? In other words, how do we distinguish a </li></ul><ul><li>helium atom from a carbon atom? </li></ul><ul><li>A- Their number of p rotons , indicated by the atomic number </li></ul>Let’s look at helium , He. It has an atomic number of 2, which means that is has 2 protons in it’s nucleus.
  4. 4. Atomic Structure Here are the basics; you need to know these. 1 H 1.0076 Hydrogen Atomic Number ( Z ) : the number of protons (p + ) Atomic Mass : the number of protons (p + ) + the number of neutrons (n 0 ) ▪ measured in atomic mass units (amu) which is one twelfth the mass of a carbon-12 atom. ▪ the mass of electrons (1/1860 p + ) is negligible. Number of Neutrons : the atomic mass - the atomic number Atomic Number Atomic Symbol Atomic Mass
  5. 5. Lets practice! Find the missing information? 8 15.999 amu O 2 2 He 39.948 amu 18 Ar Neutrons Electrons Protons Atomic Mass Atomic # Element
  6. 6. The Famous Gold Foil Experiment <ul><li>This showed us that the atom is made of mostly </li></ul><ul><li>empty space . </li></ul>
  7. 7. Isotopes Atoms of the same element with different number of neutrons <ul><li>Because they have the same number of protons, all isotopes of an element have the same chemical properties. </li></ul>
  8. 8. Mass Numbers of Hydrogen Isotopes <ul><li>What would the masses be? </li></ul>
  9. 9. The Mole: A Measurement of Matter <ul><li>At the end of this section, you should </li></ul><ul><li>be able to: </li></ul><ul><li>Describe how Avogadro’s number is related to a mole of any substance </li></ul><ul><li>Calculate the mass of a mole of any substance </li></ul>
  10. 10. The Mole (aka Avagadro’s Number) : 6.02 x 10 23
  11. 11. The Mole and Avogadro’s Number <ul><li>SI unit that measures the amount of substance </li></ul><ul><li>1 mole = 6.02 x 10 23 representative particles </li></ul><ul><li>Representative particles are usually atoms, molecules, or formula units (ions) </li></ul>
  12. 12. But Why the Mole? <ul><li>Just as 12 = 1 dozen, or 63,360 inches = 1 mile, </li></ul><ul><li>the mole allows us to count microscopic items </li></ul><ul><li>(atoms, ion, molecules) on a macroscopic scale. </li></ul><ul><li>So, 1 mole of any substance is a set number of </li></ul><ul><li>Items, namely: 6.02 x 10 23 . </li></ul><ul><li>Chemistry = awesome </li></ul>
  13. 13. Examples: 6.02 x 10 23 Ca 2+ Ion Calcium ion 6.02 x 10 23 H 2 O Molecule Water 6.02 x 10 23 N Atom Atomic nitrogen Representative Particles in 1.00 mol Chemical Formula Representative Particle Substance
  14. 14. Solve Representative Particles in 1.00 mol Formula Unit Representative Particle Substance Molecule C Carbon Molecule C 12 H 22 O 11 Sucrose Molecule CaF 2 Calcium Fluoride Molecule N 2 Nitrogen gas
  15. 15. Answers <ul><li>Nitrogen gas-molecule-N 2 </li></ul><ul><li>Calcium fluoride-formula unit-CaF 2 </li></ul><ul><li>Sucrose-molecule-C 12 H 22 O 11 </li></ul><ul><li>Carbon-atom-C </li></ul><ul><li>All have 6.02 x 10 23 representative particles in 1.00 mol </li></ul>
  16. 16. How many atoms are in a mole? <ul><li>Determined from the chemical formula </li></ul><ul><li>List the elements and count the atoms </li></ul><ul><li>Solve for CO 2 </li></ul><ul><li>C - 1 carbon atom </li></ul><ul><li>O - 2 oxygen atoms </li></ul><ul><li>Add: 1 + 2 = 3 </li></ul><ul><li>Answer: 3 times Avogadro’s number of atoms </li></ul>
  17. 17. Solve: How many atoms are in a mole of <ul><li>1. Carbon monoxide – CO </li></ul><ul><li>2. Glucose – C 6 H 12 O 6 </li></ul><ul><li>3. Propane – C 3 H 8 </li></ul><ul><li>4. Water – H 2 O </li></ul>
  18. 18. How many moles of magnesium is 1.25 x 10 23 atoms of magnesium? <ul><li>Refer to page 174 in text </li></ul><ul><li>Divide the number of atoms or molecules given in the example by 6.02 x 10 23 </li></ul><ul><li>Divide (1.25 x 10 23) by (6.02 x 10 23) </li></ul><ul><li>Express in scientific notation </li></ul><ul><li>Answer = 2.08 x 10 -1 mol Mg </li></ul>
  19. 19. Objectives <ul><li>Use the molar mass to convert between mass and moles of a substance </li></ul><ul><li>Use the mole to convert among measurements of mass, volume, and number of particles </li></ul>
  20. 20. Molar mass <ul><li>Mass (in grams) of one mole of a substance </li></ul><ul><li>Broad term (can be substituted) for gram atomic mass, gram formula mass, and gram molecular mass </li></ul><ul><li>Can be unclear: What is the molar mass of oxygen? </li></ul><ul><li>O or O 2 ? - element O or molecular compound O 2 ? </li></ul>
  21. 21. Molar Mass <ul><li>Gram atomic mass (gam) – atomic mass of an element taken from the periodic table </li></ul><ul><li>Gram molecular mass (gmm) – mass of one mole of a molecular compound </li></ul><ul><li>Gram formula mass (gfm) – mass of one mole of an ionic compound </li></ul><ul><li>Can use molar mass instead of gam, gmm, or gfm </li></ul>
  22. 22. Calculating the Molar Mass of Compounds (Molecular and Ionic) <ul><li>1. List the elements </li></ul><ul><li>2. Count the atoms </li></ul><ul><li>3. Multiply the number of atoms of the element by the atomic mass of the element (atomic mass is on the periodic table) </li></ul><ul><li>4. Add the masses of each element </li></ul><ul><li>5. Express to tenths place </li></ul>
  23. 23. What is the molar mass (gfm) of ammonium carbonate (NH 4 ) 2 CO 3 ? <ul><li>N 2 x 14.0 g = 28.0 g </li></ul><ul><li>H 8 x 1.0 g = 8.0 g </li></ul><ul><li>C 1 x 12.0 g = 12.0 g </li></ul><ul><li>O 3 x 16.0 g = 48.0 g </li></ul><ul><li>Add ________ </li></ul><ul><li>Answer 96.0 g </li></ul>
  24. 24. Practice Problems <ul><li>1. How many grams are in 9.45 mol </li></ul><ul><li>of dinitrogen trioxide (N 2 O 3 ) ? </li></ul><ul><li>a. Calculate the grams in one mole </li></ul><ul><li>b. Multiply the grams by the number </li></ul><ul><li>of moles </li></ul><ul><li>2. Find the number of moles in 92.2 g </li></ul><ul><li>of iron(III) oxide (Fe 2 O 3 ). </li></ul><ul><li>a. Calculate the grams in one mole </li></ul><ul><li>b. Divide the given grams by the grams in one mole </li></ul>
  25. 25. Answers <ul><li>1. 718 g N 2 O 3 (one mole is 76.0g) </li></ul><ul><li>2. 0.578 mol Fe 2 O 3 (one mole is 159.6 g) </li></ul>
  26. 26. Volume of a Mole of Gas <ul><li>Varies with a change in temperature or a change in pressure </li></ul><ul><li>At STP, 1 mole of any gas occupies a volume of 22.4 L </li></ul><ul><li>Standard temperature is 0 ° C </li></ul><ul><li>Standard pressure is 101.3 kPa (kilopascals), or 1 atmosphere (atm) </li></ul><ul><li>22.4 L is known as the molar volume </li></ul>
  27. 27. <ul><li>22.4 L of any gas at STP contains 6.02 x 10 23 representative particles of that gas </li></ul><ul><li>One mole of a gaseous element and one mole of a gaseous compound both occupy a volume of 22.4 L at STP (Masses may differ) </li></ul><ul><li>Molar mass (g/mol) = Density (g/L) x Molar Volume (L/mol) </li></ul>
  28. 28. Objectives <ul><li>Define the terms </li></ul><ul><li>Calculate the percent composition of a substance from its chemical formula or experimental data </li></ul><ul><li>Derive the empirical formula and the molecular formula of a compound from experimental data </li></ul>
  29. 29. Terms to Know <ul><li>Percent composition – relative amounts of each element in a compound </li></ul><ul><li>Empirical formula – lowest whole- number ratio of the atoms of an element in a compound </li></ul>
  30. 30. An 8.20 g piece of magnesium combines completely with 5.40 g of oxygen to form a compound. What is the percent composition of this compound? <ul><li>1. Calculate the total mass </li></ul><ul><li>Divide each given by the total mass </li></ul><ul><li>and then multiply by 100% </li></ul><ul><li>Check your answer: The </li></ul><ul><li>percentages should total 100% </li></ul>
  31. 31. Answer <ul><li>The total mass is 8.20 g + 5.40 g = 13.60 g </li></ul><ul><li>Divide 8.2 g by 13.6 g and then multiply by 100% = 60.29412 = 60.3% </li></ul><ul><li>Divide 5.4 g by 13.6 g and then multiply by 100% = 39.70588 = 39.7% </li></ul><ul><li>Check your answer: 60.3% + 39.7% = 100% </li></ul>
  32. 32. Calculate the percent composition of propane (C 3 H 8 ) <ul><li>1. List the elements </li></ul><ul><li>2. Count the atoms </li></ul><ul><li>3. Multiply the number of atoms of the element by the atomic mass of the element (atomic mass is on the periodic table) </li></ul><ul><li>4. Express each element as a percentage of the total molar mass </li></ul><ul><li>5. Check your answer </li></ul>
  33. 33. Answer <ul><li>Total molar mass = 44.0 g/mol </li></ul><ul><li>36.0 g C = 81.8% </li></ul><ul><li>8.0 g H = 18.2% </li></ul>
  34. 34. Calculate the mass of carbon in 52.0 g of propane (C 3 H 8 ) <ul><li>Calculate the percent composition using the formula (See previous problem) </li></ul><ul><li>2. Determine 81.8% of 82.0 g </li></ul><ul><li>Move decimal two places to the </li></ul><ul><li>left (.818 x 82 g) </li></ul><ul><li>3. Answer = 67.1 g </li></ul>
  35. 35. <ul><li>1) Find the percent composition of </li></ul><ul><li>Aluminum Oxide (Al 3 O 2 ) </li></ul><ul><li>2) How much of a 5-g piece of Iron </li></ul><ul><li>Bromide (FeBr 3 ) is iron? </li></ul>
  36. 36. Calculating Empirical Formulas <ul><li>Microscopic – atoms </li></ul><ul><li>Macroscopic – moles of atoms </li></ul><ul><li>Lowest whole-number ratio may not be the same as the compound formula </li></ul><ul><li>Example: The empirical formula of hydrogen peroxide (H 2 O 2 ) is HO </li></ul>
  37. 37. Empirical Formulas <ul><li>The first step is to find the mole-to-mole ratio of the elements in the compound </li></ul><ul><li>If the numbers are both whole numbers, these will be the subscripts of the elements in the formula </li></ul><ul><li>If the whole numbers are identical, substitute the number 1 </li></ul><ul><li>Example: C 2 H 2 and C 8 H 8 have an empirical formula of CH </li></ul><ul><li>If either or both numbers are not whole numbers, numbers in the ratio must be multiplied by the same number to yield whole number subscripts </li></ul>
  38. 38. What is the empirical formula of a compound that is 25.9% nitrogen and 74.1% oxygen? <ul><li>1. Assume 100 g of the compound, so that </li></ul><ul><li>there are 25.9 g N and 74.1 g O </li></ul><ul><li>2. Convert to mole-to-mole ratio: </li></ul><ul><li>Divide each by mass of one mole </li></ul><ul><li>25.9 g divided by 14.0 g = 1.85 mol N </li></ul><ul><li>74.1 g divided by 16.0 g = 4.63 mol O </li></ul><ul><li>3. Divide both molar quantities by the </li></ul><ul><li> smaller number of moles </li></ul>
  39. 39. <ul><li>4. 1.85/1.85 = 1 mol N </li></ul><ul><li>4.63/1.85 = 2.5 mol O </li></ul><ul><li>5. Multiply by a number that converts each to a whole number (In this case, the number is 2 because 2 x 2.5 = 5, which is the smallest whole number ) </li></ul><ul><li>2 x 1 mol N = 2 </li></ul><ul><li>2 x 2.5 mol O = 5 </li></ul><ul><li>Answer: The empirical formula is N 2 O 5 </li></ul>
  40. 40. Determine the Empirical Formulas <ul><li>1. H 2 O 2 </li></ul><ul><li>2. CO 2 </li></ul><ul><li>3. N 2 H 4 </li></ul><ul><li>4. C 6 H 12 O 6 </li></ul><ul><li>5. What is the empirical formula of a compound that is 3.7% H, 44.4% C, and 51.9% N? </li></ul>
  41. 41. Answers <ul><li>Compound Empirical Formula </li></ul><ul><li>1. H 2 O 2 HO </li></ul><ul><li>2. CO 2 CO 2 </li></ul><ul><li>3. N 2 H 4 NH 2 </li></ul><ul><li>4. C 6 H 12 O 6 CH 2 O </li></ul><ul><li>5. HCN </li></ul>
  42. 42. Calculating Molecular Formulas <ul><li>The molar mass of a compound is a simple whole-number multiple of the molar mass of the empirical formula </li></ul><ul><li>The molecular formula may or may not be the same as the empirical formula </li></ul>
  43. 43. Calculate the molecular formula of the compound whose molar mass is 60.0 g and empirical formula is CH 4 N. <ul><li>1. Using the empirical formula, calculate the empirical formula mass (efm) </li></ul><ul><li>(Use the same procedure used to calculate molar mass.) </li></ul><ul><li>2. Divide the known molar mass by the efm </li></ul><ul><li>3. Multiply the formula subscripts by this value to get the molecular formula </li></ul>
  44. 44. Answer <ul><li>Molar mass (efm) is 30.0 g </li></ul><ul><li>60.0 g divided by 30.0 g = 2 </li></ul><ul><li>Answer: C 2 H 8 N 2 </li></ul>
  45. 45. Practice Problems <ul><li>1) What is the empirical formula of a compounds that is 25.9% nitrogen and 74.1% oxygen? </li></ul><ul><li>2) Calculate the empirical formula of a compound that is 32.00% C, 42.66% O, 18.67% N, and 6.67% H. </li></ul><ul><li>3) Calculate the empirical formula of a compound that is 42.9% C and 57.1% O. </li></ul>
  46. 46. Practice Problems <ul><li>4) What is the molecular formula for each compound: </li></ul><ul><li>a) CH 2 O, 90 g/mol </li></ul><ul><li>b) HgCl, 472.2 g/mol </li></ul><ul><li>c) C 3 H 5 O 2 , 146 g/mol </li></ul>

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