Charge on the electron

In these equations the electrostatic potential i might be thought to be the potential at the actual electrodes, the platinum on the left and the silver on the right. However, electrons are not the hypothetical test particles of physics, and the electrostatic potential difference at a junction between two metals is nnmeasurable. Wliat is measurable is the difference in the electrochemical potential p of the electron, which at equilibrium must be the same in any two wires that are in electrical contact. One assumes that the electrochemical potential can be written as the combination of two tenns, a chemical potential minus the electrical potential (- / because of the negative charge on the electron). Wlien two copper wires are connected to the two electrodes, the... 

The unit positive charge on the proton balances the unit negative charge on the electron. In neutral atoms, the number of electrons is exactly equal to the number of protons. In an iron atom (Fe ), there are 26 electrons and just 26 protons. A cation is formed by removing electrons not by adding protons. An ion has one electron less than the neutral atom M . Similarly, an anion M" is formed by adding an electron and not by subtracting a proton from M°. 

Our present views on the electronic structure of atoms are based on a variety of experimental results and theoretical models which are fully discussed in many elementary texts. In summary, an atom comprises a central, massive, positively charged nucleus surrounded by a more tenuous envelope of negative electrons. The nucleus is composed of neutrons ( n) and protons ([p, i.e. H ) of approximately equal mass tightly bound by the force field of mesons. The number of protons (2) is called the atomic number and this, together with the number of neutrons (A ), gives the atomic mass number of the nuclide (A = N + Z). An element consists of atoms all of which have the same number of protons (2) and this number determines the position of the element in the periodic table (H. G. J. Moseley, 191.3). Isotopes of an element all have the same value of 2 but differ in the number of neutrons in their nuclei. The charge on the electron (e ) is equal in size but opposite in sign to that of the proton and the ratio of their masses is 1/1836.1527. 

However, the velocity, v, of the electron is still unknown. We must calculate this quantity from the work done on the electron as it was accelerated, moving from the negative electrode to the positive electrode. The work done on the electron is the product of the charge on the electron times the voltage difference, V, between the electrodes ... 

We may use this value of the charge on the electron to calculate the mass of an electron. To do so, it is necessary to know the ratio of (electron charge/electron mass) = e/m. This ratio is measured with apparatus based on principles displayed in Figures 14-4 and 14-6. Using the result e/m = 1,759 X 10 coulombs/g, the mass of an electron is found to be... 

In order to explain his experimental results, Rutherford designed a new picture of the atom. He proposed that the atom occupies a spherical volume approximately I0 8cm in radius and at the center of each atom there is a nucleus whose radius is about 10 u cm. He further proposed that this nucleus contains most of the mass of the atom, and that it also has a positive charge that is some multiple of the charge on the electron. The region of space outside the nucleus must be occupied by the electrons. We see from Figure 14-11 that Rutherford s picture requires that most of the volume of the atom be a region of very low density. 

American physicist Robert A. Millikan and his student Harvey Fletcher designed an experiment to determine the charge on the electron. As shown in Figure 2-14. the apparatus was a chamber containing two electrical plates. An atomizer sprayed a mist of oil droplets into the chamber, where the droplets drifted through a hole in the top plate. A telescope allowed the experimenters to measure how fast the droplets moved downward under the force of gravity. The mass of each droplet could then be calculated from its rate of downward motion. 

Significance of the Faraday s laws, e= F/N relationship between the Faraday, Avogadro s number and the charge on the electron Besides the practical applications so far described, Faraday s laws have an important significance in so far as theoretical interest goes. The laws have introduced the concept of atomic nature of electricity. 

Tbginteraction between the two particles in this system is described by Coulomb s law, in which the force is proportional to the inverse-square of the distance between the particles and —e2 is the product of the charges on the electron and the proton. The corresponding potential function is then of the form... 

For some systems, the potential energy is some function of a coordinate. For example, the potential energy of an electron bound to the nucleus of a hydrogen atom is given by — e2/r, where e is the charge on the electron and r is a coordinate. Therefore, when this potential function is placed in operator form, it is the same as in classical form, — e2/r (see Table 2.1). 

Historically (as well as currently by many chemists), the quantity of charge separated is expressed in electrostatic emits, esu, which is g1/2 cm3/2sec. The charge on the electron is 4.80 x 10 10esu, and when the internuclear distances are expressed in centimeters,... 

It is easy to use this equation to determine what the attraction energy would be for 1 mole of Na+(g) interacting with 1 mole of Cl-(g) at a distance of 2.79 A (279 pm). We will calculate the value first in ergs and then convert the result into kilojoules. Because the charge on the electron is 4.8 X 10 10 esu and 1 esu = 1 g1/-2 cm3/2 sec-1, the attraction energy is... 

The first modern atomic theory was developed by John Dalton and first presented in 1808. Dalton used the term atom (first used by Democritus) to describe the tiny, indivisible particles of an element. Dalton also thought that atoms of an element are the same and atoms of different elements are different. In 1897, J. J. Thompson discovered the existence of the first subatomic particle, the electron, by using magnetic and electric fields. In 1909, Robert Millikan measured the charge on the electron in his oil drop experiment (electron charge = -1.6022 x 10-19 coulombs), and from that he calculated the mass of the electron. 

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