Number of Valence Electrons amazonaws com
Number of Valence Electrons -
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Valence Electrons (VE): An electron that resides in outermost shell of an atom Fluorine (9e-): 1s22s22p5 o 1s2: n=1 o 2s22p5: 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 (Zeff) -
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Consider Mg: o 12 electrons o 1s22s22p63s2 [Ne] 3s2 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) Zeff: Net positive charge that an electron sees from the nucleus o Zeff = Z – S o Z represents number of protons in nucleus o S represents the number of shield (core) electrons For a VE in Mg, calculate Zeff o Zeff = 12 – 10 o Zeff = +2 o But Zeff is actually +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 Zeff experienced by VEs o As you go from left to right on a row, Zeff increases 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
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Decrease in Zeff 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 Ca2+ Removing VE means remaining electrons are more attracted to protons in nucleus o Anions are larger than their parent atoms Ca vs Ca Adding VE with no extra protons to attract makes the VE drift farther away For an isoelectronic series (same number of electrons)3, the most negative ion is largest o O2-, F-, Na+, Mg2+, Al3+ o All isoelectronic with Ne o O2- is largest Ions of the same charge follow normal trend (increase right to left, top to bottom) o S2 > O2- (same reason 5 > 0)
Metallic Character -
Metals easily lose electrons Tend to form positive ions Easy to oxidize Tend to react with O to form basic oxides React with H2O to form hydroxides, H2 (g) and heat o 2Na (s) + 2H2O (l) -> 2NaOH (aq) + H2 (g) Trends in metallic character: o Increase from right to left and top to bottom o Hold on VE gets weaker since it’s farther from nucleus
Ionization Energy (IE) -
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The energy required to remove an electron from a gaseous ground state or ion E (g) -> E+ (g) + e- (1st IE or IE1) E+ (g) -> E2+ (g) + e- (2nd IE or IE2) Trends: o Increase from left to right o Zeff increases so VE’s are bound tightly and take o Increase from bottom to top o Atomic radius decreases so electron is closer to nucleus and bound more tightly Exceptions in IE (Explained by electron configuration Be > B o Single 2p electron in B is easier to remove than 2p electron in Be (the 2s is closer to nucleus N>O o Removing one 2p electron in O leaves the orbital half full
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Other exceptions: Hg > Pb, etc. IE2 > IE1 o Takes a lot of energy to remove a core electron
Electron Affinity (EA) -
Willingness of a gaseous ground state atom or ion to add an electron o E (g) + e- -> E- (g) Adding an electron usually releases energy So EA’s are usually negative Trends: o As you go left to right on table, EA’s tend to increase DELTA H becomes more negative o Further to tight in periodic Table you are more likely to fill an energy shell by adding and electron o Generally we see no change from top to bottom More electron/electron repulsion At the same time have larger more spread out shells Cancel each other out
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Valence Electrons (VE): An electron that resides in outermost shell of an atom Fluorine (9e-): 1s22s22p5 o 1s2: n=1 o 2s22p5: 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 (Zeff) -
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Consider Mg: o 12 electrons o 1s22s22p63s2 [Ne] 3s2 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) Zeff: Net positive charge that an electron sees from the nucleus o Zeff = Z – S o Z represents number of protons in nucleus o S represents the number of shield (core) electrons For a VE in Mg, calculate Zeff o Zeff = 12 – 10 o Zeff = +2 o But Zeff is actually +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 Zeff experienced by VEs o As you go from left to right on a row, Zeff increases 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
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Decrease in Zeff 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 Ca2+ Removing VE means remaining electrons are more attracted to protons in nucleus o Anions are larger than their parent atoms Ca vs Ca Adding VE with no extra protons to attract makes the VE drift farther away For an isoelectronic series (same number of electrons)3, the most negative ion is largest o O2-, F-, Na+, Mg2+, Al3+ o All isoelectronic with Ne o O2- is largest Ions of the same charge follow normal trend (increase right to left, top to bottom) o S2 > O2- (same reason 5 > 0)
Metallic Character -
Metals easily lose electrons Tend to form positive ions Easy to oxidize Tend to react with O to form basic oxides React with H2O to form hydroxides, H2 (g) and heat o 2Na (s) + 2H2O (l) -> 2NaOH (aq) + H2 (g) Trends in metallic character: o Increase from right to left and top to bottom o Hold on VE gets weaker since it’s farther from nucleus
Ionization Energy (IE) -
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The energy required to remove an electron from a gaseous ground state or ion E (g) -> E+ (g) + e- (1st IE or IE1) E+ (g) -> E2+ (g) + e- (2nd IE or IE2) Trends: o Increase from left to right o Zeff increases so VE’s are bound tightly and take o Increase from bottom to top o Atomic radius decreases so electron is closer to nucleus and bound more tightly Exceptions in IE (Explained by electron configuration Be > B o Single 2p electron in B is easier to remove than 2p electron in Be (the 2s is closer to nucleus N>O o Removing one 2p electron in O leaves the orbital half full
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Other exceptions: Hg > Pb, etc. IE2 > IE1 o Takes a lot of energy to remove a core electron
Electron Affinity (EA) -
Willingness of a gaseous ground state atom or ion to add an electron o E (g) + e- -> E- (g) Adding an electron usually releases energy So EA’s are usually negative Trends: o As you go left to right on table, EA’s tend to increase DELTA H becomes more negative o Further to tight in periodic Table you are more likely to fill an energy shell by adding and electron o Generally we see no change from top to bottom More electron/electron repulsion At the same time have larger more spread out shells Cancel each other out
