2. Avogadro’s Number The Mole

3. Avogadro’s Number N A Amadeo Avogadro (1766-1856) never knew his own number; it was named in his honor by a French scientist in 1909. Its value was first estimated by Josef Loschmidt, an Austrian chemistry teacher, in 1895. Amadeo Avogadro (1766-1856) never knew his own number; it was named in his honor by a French scientist in 1909. Its value was first estimated by Josef Loschmidt, an Austrian chemistry teacher, in 1895.

4. Atom’s & Molecule’s Small Size Owing to their tiny size, atoms and molecules cannot be counted by direct observation. Owing to their tiny size, atoms and molecules cannot be counted by direct observation. Many scientists worked on the problem of counting atoms, formula units and molecules. Many scientists worked on the problem of counting atoms, formula units and molecules.

5. Avogadro The Avogadro constant, N A, is a fundamental physical constant that relates any quantity at the atomic scale to its corresponding macroscopic scale, inspired by the kinetic gas theory Avogadro proposed his hypothesis in 1811, in order to describe chemical reactions as an atomic process between atoms or molecules. The Avogadro constant, N A, is a fundamental physical constant that relates any quantity at the atomic scale to its corresponding macroscopic scale, inspired by the kinetic gas theory Avogadro proposed his hypothesis in 1811, in order to describe chemical reactions as an atomic process between atoms or molecules.

6. Loschmidt The review of methods aimed at finding a value for N A starts with the calculations made by Loschmidt (1865; N A 72×10 23 mol -1 ) who evaluated the number of molecules in a given gas volume. The review of methods aimed at finding a value for N A starts with the calculations made by Loschmidt (1865; N A 72×10 23 mol -1 ) who evaluated the number of molecules in a given gas volume.

7. Perrin Consideration of Brownian motion (a random movement of microscopic particles suspended in liquids or gases resulting from the impact of the fluids surrounding the particles) led to some more accurate determinations of N A around the beginning of the 20th century (Perrin (1908); N A 6.7×10 23 mol -1 ). Consideration of Brownian motion (a random movement of microscopic particles suspended in liquids or gases resulting from the impact of the fluids surrounding the particles) led to some more accurate determinations of N A around the beginning of the 20th century (Perrin (1908); N A 6.7×10 23 mol -1 ).

8. Millikan Other methods developed in the following years are based on Millikan's oil drop experiment (1917, N A 6.064(6)×10 23 mol -1 ). Other methods developed in the following years are based on Millikan's oil drop experiment (1917, N A 6.064(6)×10 23 mol -1 ).

9. Rutherford Rutherford counted the of alpha particles emitted from radium or uranium. (Rutherford (1909); N A 6.16×10 23 mol -1 ). Rutherford counted the of alpha particles emitted from radium or uranium. (Rutherford (1909); N A 6.16×10 23 mol -1 ).

10. Nuoy Nuoy’s Investigations of molecular monolayers on liquids refined Avogadro’s number even further (Nuoy (1924); N A 6.004×10 23 mol -1 ). Nuoy’s Investigations of molecular monolayers on liquids refined Avogadro’s number even further (Nuoy (1924); N A 6.004×10 23 mol -1 ).

11. Final Result The combination of data from several independent measurements of the unit cell and the molar volumes has led to a value for the Avogadro constant of N A = 6.022 1335(30)×10 23 mol -1 (De Bièvre et al 2001) recommended by the national metrology institutes involved in this research project (Becker 2001). The combination of data from several independent measurements of the unit cell and the molar volumes has led to a value for the Avogadro constant of N A = 6.022 1335(30)×10 23 mol -1 (De Bièvre et al 2001) recommended by the national metrology institutes involved in this research project (Becker 2001).

12. Using Avogadro’s Number A mole is a number. Like the number 12 for a "dozen“. They are both dimensionless (no units). A mole is a number. Like the number 12 for a "dozen“. They are both dimensionless (no units). It is a huge number, far greater in magnitude than we can visualize. It is a huge number, far greater in magnitude than we can visualize. Its practical use is limited to counting very tiny things like atoms, molecules, formula units, electrons, or photons. Its practical use is limited to counting very tiny things like atoms, molecules, formula units, electrons, or photons.

13. Comparing Moles & Dozens One dozen roses = _____ roses. One dozen roses = _____ roses. ½ dozen roses = _____ roses. ½ dozen roses = _____ roses. 3.5 dozen roses = _____ roses. 3.5 dozen roses = _____ roses. 10 dozen roses = _____ roses. 10 dozen roses = _____ roses. One mole of roses = _____ roses. One mole of roses = _____ roses. ½ mole of roses = _____ roses. ½ mole of roses = _____ roses. 3.5 moles of roses = _____ roses. 3.5 moles of roses = _____ roses. 10 moles of roses = _____ roses. 10 moles of roses = _____ roses.

14. Conversion Factors & the Mole If we want to find the number of roses in 7.5 dozen roses, we set up a conversion factor. A conversion factor is used to convert between units. Conversion factors always equal one. If we want to find the number of roses in 7.5 dozen roses, we set up a conversion factor. A conversion factor is used to convert between units. Conversion factors always equal one. 7.5 dozen roses x ___12 roses___ = 7.5 dozen roses x ___12 roses___ = one dozen roses one dozen roses Since one dozen is equal to12, our conversion factor equals one. Since one dozen is equal to12, our conversion factor equals one.

15. The Mole If the mole relates to the microscopic world of atoms and molecules, how is it useful in the macroscopic world we live in? If the mole relates to the microscopic world of atoms and molecules, how is it useful in the macroscopic world we live in? The mole, commonly abbreviated mol, is the SI unit used to measure the amount of a substance. The mole, commonly abbreviated mol, is the SI unit used to measure the amount of a substance.

16. A Mole of Atoms A mole is the number of particles in exactly 12 grams of a particular isotope of carbon (C-12). If you have 12.0 g of C-12 (carbon 12) you have 6.022 x 10 23 carbon atoms. A mole is the number of particles in exactly 12 grams of a particular isotope of carbon (C-12). If you have 12.0 g of C-12 (carbon 12) you have 6.022 x 10 23 carbon atoms. How many moles of C do you have if you have 6.00 g of C? How many moles of C do you have if you have 6.00 g of C?

17. Elements & the Mole For all elements, a mole is the atomic mass of the element expressed in grams. If you have one mole of magnesium, how many Mg atoms do you have? If you have 24.31 g of Mg, how many atoms of Mg do you have? If you have one mole of Mg, what mass of Mg do you have?

18. Compounds & the Mole A mole of a compound is 6.02 x 10 23 units of that compound (molecules or formula units). A mole of a compound is 6.02 x 10 23 units of that compound (molecules or formula units). The compound magnesium chloride is written ________. The compound magnesium chloride is written ________. How many formula units of MgCl 2 would one mole of MgCl 2 have? How many formula units of MgCl 2 would one mole of MgCl 2 have?

19. Conversion Factors & the Mole We know one mole of any substance is 6.02 x 10 23 particles of that substance. If you wanted to know how many Mg atoms 7.5 moles of Mg contained : We know one mole of any substance is 6.02 x 10 23 particles of that substance. If you wanted to know how many Mg atoms 7.5 moles of Mg contained : 7.5 moles Mg x 6.02 x 10 23 atoms = 7.5 moles Mg x 6.02 x 10 23 atoms = 1 mole Mg 1 mole Mg