The development of Dalton's atomic theory and Avogadro's molecular law had overriding influence on the development of chemistry, in addition to their importance in physics.
Avogadro's Law
Avogadro's law, which was easily proved by kinetic theory, indicated that a specified volume of a gas at a given temperature and pressure always contained the same number of molecules, irrespective of the gas selected. This number, however, could not be accurately determined, and the 19th-century physicists therefore had no sound knowledge of molecular or atomic mass and size until the turn of the 20th century, when subsequent to the discovery of the electron, the American physicist Robert Andrews Millikan carefully determined its charge. This finally permitted accurate determination of the so-called Avogadro's number, which is the number of molecules in that amount of material exactly equal to its molecular weight.
Besides the mass, another quantity of interest was the size of an atom. Various and only partly successful attempts at finding the size of an atom were made during the latter part of the 19th century; the most successful applied the results of kinetic theory to nonideal gases—that is, gases the behavior of which depended on the fact that molecules were not points but had finite volumes. Only later experiments involving the scattering of X rays, alpha particles, and other atomic and subatomic particles by atoms led to more precise measurements of their size as being between 10-8 and 10-7 cm (4 × 10-7 and 4 × 10-6 in) in diameter. A precise statement about the size of an atom, however, requires some explicit definition of what is meant by size, since most atoms are not exactly spherical and can exist in various states that change the distance between the nucleus and the electrons within the atom.
Avogadro's Law
Avogadro's law, which was easily proved by kinetic theory, indicated that a specified volume of a gas at a given temperature and pressure always contained the same number of molecules, irrespective of the gas selected. This number, however, could not be accurately determined, and the 19th-century physicists therefore had no sound knowledge of molecular or atomic mass and size until the turn of the 20th century, when subsequent to the discovery of the electron, the American physicist Robert Andrews Millikan carefully determined its charge. This finally permitted accurate determination of the so-called Avogadro's number, which is the number of molecules in that amount of material exactly equal to its molecular weight.
Besides the mass, another quantity of interest was the size of an atom. Various and only partly successful attempts at finding the size of an atom were made during the latter part of the 19th century; the most successful applied the results of kinetic theory to nonideal gases—that is, gases the behavior of which depended on the fact that molecules were not points but had finite volumes. Only later experiments involving the scattering of X rays, alpha particles, and other atomic and subatomic particles by atoms led to more precise measurements of their size as being between 10-8 and 10-7 cm (4 × 10-7 and 4 × 10-6 in) in diameter. A precise statement about the size of an atom, however, requires some explicit definition of what is meant by size, since most atoms are not exactly spherical and can exist in various states that change the distance between the nucleus and the electrons within the atom.
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