3. Tuesday, April 27, 2010 Warmup: Read Today’s Agenda. What do you expect to do and to learn today? Do you think class will be easy or difficult, and will the information be old or new to you? Who do you expect to work with today? Compare your expectations today to yesterday and tomorrow. Page 293 #21-30 is due today. Mole problem presentation: pretest/ posttest is due. Discuss mole pres, mid-trimester assessment Sample mole presentation by Mrs. Gall
4.
5. What is Avogadro’s Number? Presented by Mrs. Gall: Tuesday, April 27, 2010 Pretest Powerpoint Presentation Questions answered Post-test
6. Pretest: What is Avogadro’s Number? What is Avogadro’s Number? How many items are in a mole? How many Carbon atoms are in a mole of Carbon atoms? How many donuts are in a mole of donuts?
7. The following slides… Information from Wikipedia More information than is necessary Information is still incomplete here! My goal: share enough information and resources to help you find more information if you are interested.
8. Avogadro constant Values of NA[1] Units 6.022 141 79(30) × 1023 mol−1 2.731 597 57(14) × 1026 lb-mol−1 1.707 248 479(85) × 1025 oz-mol−1 For details, see Terminology and units below. In chemistry and physics, the Avogadro constant (symbols: L, NA), also called Avogadro's number, is the number of "elementary entities" (usually atoms or molecules) in one mole, that is (from the definition of the mole), the number of atoms in exactly 12 grams of carbon-12.[2][3] The 2006 CODATA recommended value is:[1]
9. More from wikipedia: The value of the Avogadro constant was first indicated by Johann Josef Loschmidt who, in 1865, estimated the average diameter of the molecules in air by a method that is equivalent to calculating the number of particles in a given volume of gas.[7] This latter value, the number density of particles in an ideal gas, is now called the Loschmidt constant in his honour, and is approximately proportional to the Avogadro constant. The connection with Loschmidt is the root of the symbol L sometimes used for the Avogadro constant, and German language literature may refer to both constants by the same name, distinguished only by the units of measurement.[8]
10. Amadeo Avogadro The Avogadro constant is named after the early nineteenth century Italian scientist Amedeo Avogadro, who, in 1811, first proposed that the volume of a gas (at a given pressure and temperature) is proportional to the number of atoms or molecules regardless of the nature of the gas.[4] The French physicist Jean Perrin in 1909 proposed naming the constant in honour of Avogadro.[5] Perrin won the 1926 Nobel Prize in Physics, in a large part for his work in determining the Avogadro constant by several different methods.[6]
11. Terminology and units Perrin originally proposed the name "Avogadro's number" (N) to refer to the number of molecules in one gram-molecule of oxygen (exactly 32 grams of oxygen, according to the definitions of the period),[5] and this term is still widely used, especially in introductory works.[9] The change in name to "Avogadro constant" (NA) came with the introduction of the mole as a separate base unit in the International System of Units (SI) in 1971,[10] which recognized amount of substance as an independent dimension of measurement.[11] With this recognition, the Avogadro constant was no longer a pure number but a physical quantity associated with a unit of measurement, the reciprocal mole (mol−1) in SI units.[11]
12. HOW WAS AVOGADRO’S NUMBER CALCULATED? There are several ways. One (with a picture I find interesting) is on the next slide:
13. X-ray crystal density method Ball-and-stick model of the unit cell of silicon. X-ray diffraction experiments can determine the cell parameter, a, which can in turn be used to calculate a value for Avogadro's constant One modern method to calculate the Avogadro constant is to use ratio of the molar volume, Vm, to the unit cell volume, Vcell, for a single crystal of silicon:[14] The factor of eight arises because there are eight silicon atoms in each unit cell. The unit cell volume can be obtained by X-ray crystallography; as the unit cell is cubic, the volume is the cube of the length of one side (known as the unit cell parameter, a. In practice, measurements are carried out on a distance known as d220(Si), which is the distance between the planes denoted by the Miller indices {220}, and is equal to a/√8. The 2006 CODATA value for d220(Si) is 192.015 5762(50) pm, a relative uncertainty of 2.8 × 10–8, corresponding to a unit cell volume of 1.601 933 04(13) × 10–28 m3. The isotope proportional composition of the sample used must be measured and taken into account. Silicon occurs with three stable isotopes – 28Si, 29Si, 30Si – and the natural variation in their proportions is greater than other uncertainties in the measurements. The atomic weightAr for the sample crystal can be calculated, as the relative atomic masses of the three nuclides are known with great accuracy. This, together with the measured densityρ of the sample, allows the molar volume Vm to be found by: where Mu is the molar mass constant. The 2006 CODATA value for the molar volume of silicon is 12.058 8349(11) cm3mol−1, with a relative standard uncertainty of 9.1 × 10–8.[15]
15. 6.02 x 1023 Avogadro’s Number is 6.02 x 1023 There are 6.02 x 1023 items in a mole of items There are 6.02 x 1023 Carbon atoms in a mole of Carbon atoms There are 6.02 x 1023 donuts in a mole of donuts
16. Post-test: What is Avogadro’s Number? What is Avogadro’s Number? How many items are in a mole? How many Carbon atoms are in a mole of Carbon atoms? How many donuts are in a mole of donuts?
17. Tuesday, April 27, 2010Physical Science Warmup: Read Today’s Agenda. What do you expect to do and to learn today? Do you think class will be easy or difficult, and will the information be old or new to you? Who do you expect to work with today? Compare your expectations today to yesterday and tomorrow. Field Trip Handouts; assignment for nonattenders TOMORROW is pgs. 789-793 all Practice Problems. Camp Tamarack Information online Wetlands, reptiles, amphibians, mammals: KWL
18. K – W – L : 60 pts. (20 each) Camp Tamarack in Ortonville Field Trip Topics: Wetlands, reptiles, amphibians, mammals: I KNOW – I WANT to know – I LEARNED - - In each column, list 20 or more ideas regarding the topics above. This is required for all field trip attendees and optional for others. DUE, completed, tomorrow at 3 pm.
