29-31 - Chapter 29 structure of the atom: whats inside...

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Chapter 29 structure of the atom: what’s inside electrons – carry electric charge of –e - protons – carry electric charge of +e - neutrons – no net electric charge, mass same of proton - quantum mechanics – understanding of how electrons, protons, and neutrons combined to form atoms - “plum-pudding” – positive charge is distributed as a sort of “pudding” with electrons suspended within positively charged pudding throughout the atom - negative charge of electrons must be exactly canceled by the positive charge because neutral atom has a total electric charge of zero - Rutherford concluded that atoms contain a nucleus that is positively charged and has a large mass (greater than an electron) - planetary model of the atom – electrons must move in orbits to avoid “falling” into the nucleus as a result of the electric force - number of protons in the nucleus is equal to the number of electrons in the neutral atom - atomic number (Z) – number of protons in the nucleus - protons repel one another, protons are attracted to neutrons - SEE PICTURE pg 989 - attractive force: F=mv 2 /r - electric force: F= kq proton q electron /r 2 - charge on an electron is q electron = -e charge on a proton q proton =+q F=ke 2 /r 2 =mv 2 /r - electron’s speed: v 2 =ke 2 /mr - ionization energy: energy required to remove an electron from an atom in the gas phase - mechanical terms: energy needed to completely separate the two charges; to take the electron in hydrogen from its original orbit to an infinite distance from the proton problems with the planetary model of the atom - atoms such as hydrogen can be extremely stable, but in Rutherford’s model the electrons are undergoing accelerated motion - quantum theory avoids the problem of unstable electron orbits by replacing them with discrete energy levels - electrons lose or gain energy only when they undergo a transition between energy levels atomic spectra - electron in an atom can exist only in discrete energy levels: radiation an atom emits or absorbs when an electron undergoes a transition from different energy levels - approximate blackbody spectrum of the Sun – continuous curve with a smooth distribution of intensity over a wide range of wavelengths and frequencies - also contains sharp dips superimposed – called spectral “lines” - dark spectral lines called absorption lines – result from absorption of light - emission lines – emission occurs only at certain wavelengths - E photon = hf - total energy must be conserved, so final energy of the atom is lower than the initial energy by an amount of E photon - under certain conditions, photons emitted or absorbed have only certain discrete wavelengths or frequencies - quantized – energy of the atom itself can only have certain discrete values Bohr’s model of the atom - any model of the atom based on Newton’s mechanics is a failure - assumed electron orbits are circular - only certain discrete values of r are allowed, so the electron’s kinetic and potential energies can only have certain values (total energy can only have certain values)
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29-31 - Chapter 29 structure of the atom: whats inside...

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