Avogadro Constant

3 Key excerpts on "Avogadro Constant"

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  Laboratory Techniques with Reagents and Solutions

  • Chavan, U D(Authors)
  • 2021(Publication Date)
  • Daya Publishing House

    (Publisher)

  AVOGADRO’S NUMBER In chemistry and physics, the Avogadro Constant (symbols: L , N A ) is the number of constituent particles, usually atoms or molecules, that are contained in the amount of substance given by one mole. Thus it is the proportionality factor that relates the molar mass of a material to its mass. It has the dimension of reciprocal amount of substance. Avogadro’s constant has the value 6. 022140857(74) ×10 23 mol −1 in the International System of Units (SI). Previous definitions of chemical quantity involved Avogadro’s number, a historical term closely related to the Avogadro Constant but defined differently: Avogadro’s number was initially defined by Jean Baptiste Perrin as the number of atoms in one gram-molecule of atomic hydrogen, meaning (in modern terminology) one gram of (atomic) hydrogen. It was later redefined as the number of atoms in 12 grams of the isotopecarbon-12 ( 12 C) and still later generalized to relate amounts of a substance to their molecular weight. For instance, to a first approximation, 1 gram of hydrogen element (H), which has a mass number of 1 (atomic number 1), has 6.022×10 23 hydrogen atoms. Similarly, 12 grams of 12 C, with the mass number of 12 (atomic number 6), has the same number of carbon atoms, 6.022×10 23 . Avogadro’s number is a dimensionless quantity and has the numerical value of the Avogadro Constant given in base units. The Avogadro Constant is fundamental to understanding both the makeup of molecules and their interactions and combinations. For instance, since one atom of This ebook is exclusively for this university only. Cannot be resold/distributed. Equivalent Concentration 69 oxygen will combine with two atoms of hydrogen to create one molecule of water (H 2 O), one can similarly see that one mole of oxygen (6.022×10 23 of O atoms) will combine with two moles of hydrogen (2 × 6.022×10 23 of H atoms) to make one mole of H 2 O.

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  Chemistry

  Structure and Dynamics

  • James N. Spencer, George M. Bodner, Lyman H. Rickard(Authors)
  • 2011(Publication Date)
  • Wiley

    (Publisher)

  All that matters is the fact that there are the same number of particles in a mole of each of these elements. The only way to determine the number of particles in a mole is to measure the same quantity on both the atomic and the macroscopic scales. In 1910 Robert Millikan measured the charge in coulombs on a single electron: Because the charge on a mole of electrons, 96,485.3415 C, was already known, it was possible to estimate the number of electrons in a mole for the first time. Using more recent data, we get the following results. The number of particles in a mole is known as Avogadro’s number, 6.0221  10 23 , and is a pure number. The unit conversion factor, 6.0221  10 23 mol 1 , is known as Avogadro’s constant. Avogadro’s number is so large it is difficult to comprehend. It would take 6 million million galaxies the size of the Milky Way to yield 6.02  10 23 stars. At the speed of light, it would take 102 billion years to travel 6.02  10 23 miles. There are only about 40 times this number of drops of water in all the oceans on Earth. In everyday life units such as dozen (12) are used to describe a collection of items. The mole is sometimes referred to as the “chemist’s dozen.” The concept 96,485.3415 C 1 mol * 1 electron 1.60217733 * 10 - 19 C = 6.02213873 * 10 23 electrons mol 1.6 * 10 - 19 C. 2.2 THE MOLE AS A COLLECTION OF ATOMS 33 Fig. 2.1 Because each beaker contains 1 mole of the element, the two beakers contain the same number of atoms. 12.011 g Carbon 26.982 g Aluminum ➤ CHECKPOINT What is the atomic weight and molar mass of potassium? Of uranium? of the mole can be applied to any particle. We can talk about a mole of Mg atoms, a mole of Na + ions, a mole of electrons, or a mole of glucose molecules (C 6 H 12 O 6 ) Each time we use the term, we refer to Avogadro’s number of items. 1 mole of atoms contains 6.02  10 23 Mg atoms. 1 mole of ions contains 6.02  10 23 Na + ions. 1 mole of electrons contains 6.02  10 23 electrons.

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  Chemistry

  The Molecular Nature of Matter

  • Neil D. Jespersen, Alison Hyslop(Authors)
  • 2021(Publication Date)
  • Wiley

    (Publisher)

  Mole (mol) n The amount of substance of exactly 6.02214076 × 10 23 elementary entities. This number is the fixed numerical value of the Avogadro Constant, N A , when expressed in the unit mol −1 . Candela (cd) I V Defined by taking the fixed numerical value of the luminous efficacy of monochromatic radiation of frequency 540 × 10 12 Hz, K cd , to be 683 when expressed in the unit lm W −1 , which is equal to cd sr W −1 , or cd sr kg −1 m −2 s 3 , where the kilogram, meter, and second are defined in terms of h, c, and ∆ν Cs . 1 National Institute of Standards and Technology, https://www.nist.gov/pml/weights-and-measures/metric-si/si-units, accessed June 2021. 2 Le Système international d’unités, The International System of Units, 9e édition, 2019. The seven defining constants for the SI base units are presented in Table 2. Table 2 The Seven Fundamental Constants Used to Define the SI Base Units Defining Constant Symbol Numerical Value and Unit Hyperfine transition frequency of Cs-133 1 ∆ν Cs 9,192,631,770 Hz Speed of light in vacuum c 299,792,458 m/s Planck constant h 6.62607015 × 10 –34 J s Elementary charge e 1.602176634 × 10 –19 C Boltzmann constant K B 1.380649 × 10 –23 J K –1 Avogadro Constant N A 6.02214076 × 10 23 mol –1 Luminous efficacy 2 K cd 683 lm W –1 1 The unperturbed ground state hyperfine transition frequency of the cesium-133 atom ∆ν Cs is 9,192,631,770 Hz (9,192,631,770 s –1 ). 2 The luminous efficacy of monochromatic radiation of frequency 540 × 10 12 Hz, K cd , is 683 lm/W. Using the fundamental constants, we can now define the seven base SI units (Figure 2 and Table 3). Finally, one more change that has been standardized is how numbers are written. For large numbers and small numbers less than one with many decimal places, spaces are used to separate the numbers. For example, 9,192,631,770 Hz would be written as 9 192 631 770 Hz and 1.602176634 × 10 −19 C would be written as 1.602 176 634 × 10 −19 C.

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