The same model for the 2p electron suggests only about 0.5% of its time inside the shielding. Modeling this situation by dividing the electron's time between perfect shielding and no shielding, the percentage of time inside the shielding is calculated to be about 6% for the 2s electron. If there were no shielding of the 2s electron, it would be exposed to the entire nuclear charge and have energy -30.6 eV. ![]() The illustration above uses the hydrogen wavefunctions, which are not exactly correct for lithium but can be used to obtain a qualitative understanding of the dependence of the electron energies on the orbital quantum number. The 2s electron is lowered about 1.7 eV below the n=2 hydrogenic energy level of -3.4 eV which it would have if the shielding were perfect. ![]() Both levels penetrate enough to be significantly lower than the n=2 hydrogen energy which they would have if the shielding were perfect. The lithium 2s level is significantly lower than the 2p because of greater penetration past the shielding of the 1s electron. Why do levels vary with orbital quantum number? The ionization potential given by NIST was 5.395 eV. Discrepancies may remain with the other levels. The levels up through the 3d plus the 4p and 4d were rescaled to fit the data in the table of neutral lithium levels from NIST. The general layout here was taken from Rohlf but some discrepancies were found in the lower levels. The theoretical separation efficiency is about 8.0 percent. Assume that a lithium atom initially at rest radiates a photon. Since lithium-6 atoms have a greater mean free path, they are collected preferentially. One of the stable isotopes of lithium has 3 protons and 4 neutrons, so its atomic mass is 7. ![]() This is true for high angular momentum states as shown, but the s and p states fall well below the corresponding hydrogen energy levels. Lithium atoms evaporate from the liquid surface and are collected on a cold surface positioned a few centimetres above the liquid surface. Since the outer electron looks inward at just one net positive charge, it could be expected to have energy levels close to those of hydrogen. The lithium atom has a closed n=1 shell with two electrons and then one electron outside. In the present work, using only Doppler-cooling beams, we demonstrate in situ detection of single 7Li atoms in a 1D optical lattice with single atom precision. The atomic number represents the number of protons in an atom, so Lithium has 3. Hydrogen-Like Atoms:Lithium Lithium Energy Levels On a periodic table, we can see that the atomic number for lithium is 3.
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