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Information on the atomic structure of various elements, including the number of protons, neutrons, and electrons in their atoms, and the concept of shielding and effective nuclear charge. It also includes instructions on how to calculate the energy required to excite an electron in a hydrogen atom using the bohr model.
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During Class Invention
Shielding
Name(s) with Lab section in Group
Atom Nuclear Charge #protons #neutrons # electrons
By adding enough energy to ionize the atom (remove an electron). To excite an electron in an atom we need to add an amount of energy that is exactly equal to the energy separation between two energy level. (See the Bohr Model DCI to calculate the energy required to excite an electron from n = 1 to n = 4 level.)
a) a hydrogen atom energy + H(g) → H+(g) + 1e–
d) a helium atom energy + He(g) → He+(g) + 1e–
e) a neon atom energy + Ne(g) → Ne+(g) + 1e–
a) Hydrogen Z = +1 there are no inner core electrons so the core charge is +1.
b) Lithium Z = +3. The electron configuration for lithium is 1s^2 2s^1. There are two inner core electrons shielding the valence electron from some of the nuclear charge so the core charge for the valence electron in lithium is +1. c) Beryllium Z = +4. The electron configuration for beryllium is 1s^2 2s^2. There are two inner core electrons shielding the valence electron from some of the nuclear charge so the core charge for the valence electron in beryllium is +2. d) Fluorine Z = +9. The electron configuration for fluorine is 1s^2 2s^2 2p^5. There are two inner core electrons shielding the valence electron from some of the nuclear charge so the core charge for the valence electron in fluorine is +9.
e) sulfur Z = +16. The electron configuration for sulfur is 1s^2 2s^2 2p^6 3s^2 3p^4. There are ten inner core electrons shielding the valence electron from some of the nuclear charge so the core charge for the valence electron in sulfur is +6.
Shielding is what the inner core electrons do to part of the nuclear charge experienced by the valence electrons. Consider carbon in the Table in DCI25.1. There are 2 inner core electrons (electrons in the n = 1 level), 4 valence electrons and 6 protons in the nucleus. The 2 inner core electrons are shielding the 4 valence electrons from the nucleus. The result is that each of the valence electrons experience an effective nuclear charge of +4.
Element
Nuclear Charge (same as the atomic number)
Total # of electrons (same as the atomic number)
core electrons
Electrons (Outer most electrons)
Effective Nuclear Charge (Z – IC electrons)
hydrogen +1 1 0 1 + lithium +3 3 2 1 + Beryllium +4 4 2 2 + Boron +5 5 2 3 + Carbon +6 6 2 4 + Nitrogen +7 7 2 5 + Oxygen +8 8 2 6 + Fluorine +9 9 2 7 + Sulfur +16 16 10 6 + Potassium +19 19 18 1 + Bromine +35 35 28 7 +