Atomism Avogadro

The number of objects per mole, 6.0221 X 1023 mol-1, is called Avogadro s constant, NA, in honor of the nineteenth-century Italian scientist Amedeo Avo-gadro (Fig. E.3), who helped to establish the existence of atoms. Avogadro s constant is used to convert between the chemical amount (the number of moles) and the number of atoms, ions, or molecules in that amount ... 

The question immediately arose Are particles of the elements the same as Dalton s atoms Avogadro believed that they were not rather, he proposed that elements could exist as diatomic molecules. Avogadro s hypothesis could explain Gay-Lussac s law of combining volumes (Fig. 1.7). Thus, the reactions we wrote out in words become... 

If you want to count atoms, Avogadro s number must be part of the solution. Keep in mind that 1 mole of any element represents 6.022 x 1023 atoms of that element. This fact provides the necessary equality to develop two conversion factors. In terms of iron, Fe ... 

To count extremely small particles, such as atoms, Avogadros number must be an enormous quantity. As you might imagine, Avogadros number would not be convenient for measuring a quantity of marbles. Avogadros number of marbles would cover the surface of Earth to a depth of more than six kilometers Figure 10.2, however, shows that it is convenient to use the mole to measure amounts of substances. One-mole quantities of water, copper, and salt are shown, each with a different representative particle. The representative particle in a mole of water is the water molecule, the representative particle in a mole of copper is the copper atom, and the representative particle in a mole of sodium chloride is the NaCl formula unit. 

In the 1620s, the French philosopher, Rene Descartes, coined the word molecule. The existence of molecules was not accepted until the early nineteenth century when John Dalton proposed an Atomic theory in 1803, which stated that all matter was composed of small indivisible particles called atoms. Avogadro s law extended Descartes law of... 

The activated complex K for the activated complex The Debye atomic jump frequency, 10 Hz The potential gradient per atom Avogadro s number... 

The link between the mass of a sample and the number of moles present is the molar mass of the substance in question. To determine the molar mass of a compound, we can exploit the idea of conservation of mass. Consider one mole of water as an example. We know that one mole of the compound must contain Avo-gadro s number of H2O molecules. Furthermore, we know that each of those molecules must contain one O atom and two H atoms. Avogadro s number of oxygen atoms is one mole, and we know from the periodic table that one mole of O atoms has a mass of 16.0 g. Because each molecule contains two hydrogen atoms, the entire one mole sample will contain two moles of H atoms. Again consulting the periodic table, we see that a mole of H atoms has a mass of 1.0 g, so two moles must have a mass of 2.0 g. The masses of the O and H atoms must be the same as the mass of the mole of H2O, so we can simply add them to get 18.0 g as the mass of one mole of H2O. In other words, the molar mass of H2O is 18.0 g/mol. We can do the same thing for any compound the sum of the molar masses of all of the atoms is the molar mass of the compound. In Example Problem 3.5, we determine the molar mass of several explosive compounds. 

One mole (mol) is the amount of material of a system containing the same number of elementary entities as there are atoms in 0.012 kg of carbon 12 - i.e. 6.02217 x 10 atoms (Avogadro s number). 

This definition of the mole establishes a relationship between mass (grams of carbon) and number of atoms (Avogadro s number). This relationship, as we will see shortly, allows us to count atoms by weighing them. 

The number of particles in a mole is known as Avogadro s number, named for the nineteenth-century Italian scientist Amedeo Avogadro, whose ideas were crucial in explaining the relationship between mass and numbers of atoms. Avogadro s number—6.022141 79 x lO —is the number of particles in exactiy one moie of a pure substance. For most purposes, Avogadro s number is rounded to 6.022 x 10. ... 

---