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Chemistry (181)
CHM 113 (103)
Ron Briggs (24)

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CHM 113
Ron Briggs

Number of Valence Electrons - Valence Elect-ons (2E)2 An5electron that resides in outermost shell of an atom - Fluorine (9e ): 1s 2s 2p o 1s : n=1 o 2s 2p : n=2 o 7 VE’s - Number of VE equals group number on Periodic Table o Halogens: 7 VE o O, S, etc: 6 VE o Alkaline medals (Na, K): 1 VE o Noble gases: 8 VE (Except He, which has 2) Effective Nuclear Charge (Z ) eff - Consider Mg: o 12 el2ct2ons6 2 o 1s 2s 2p 3s  [Ne] 3s 2 o 2 VE (n=3) o 10 core electrons o 12 protons in nucleus - Electrons repulsed by other electrons - Electrons attracted by protons in nucleus (but not all equally) - VE are shielded from nucleus by core electrons - VE are shielded from nucleus by other VE (only weakly) - Z effet positive charge that an electron sees from the nucleus o Z = Z – S eff o Z represents number of protons in nucleus o S represents the number of shield (core) electrons - For a VE in Mg, calculate Z eff o Z = 12 – 10 eff o Z = eff o But Z isefftually +3.3 o The probability plot of the 3s electron has regions close to the nucleus, meaning the electron sees a larger positive charge - Trends in Z eeffrienced by VEs o As you go from left to right on a row, Z increffes  Number of electrons (and shielding) stays the same but number of protons increases o As you go from top to bottom (down a group), Z-S remains the same  Larger electron cores don’t shield as well Atomic radius (size) - Distance from the center of the nucleus to the outermost electron in an atom - Trends: o Increased in AR from right to left  Decrease in Z eff  Less attraction if the outer electrons to the nucleus o Increase in AR from top to bottom  Filling electrons in shells that are farther from the nucleus - What about ions? o Cations smaller than parent atoms:  Ca vs Ca 2+  Removing VE means remaining electrons are more attracted to protons in nucleus o Anions are larger than their parent atoms  Ca vs Ca -
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