University:
Boston University
Course:
CAS PY 105 | Physics 1
Academic year:

2020
Views:

274

Pages:

7
Author:

Brianna Sherman

What we know about electron waves so far (Big idea #1) More loops (n) = more energy (and bigger) En = –(2.18 aJ)(Z2/n2) (Big idea #2) Bigger nuclear charge (Z) = lower energy (and smaller) (Big idea #3) Electrons will always be the lowest possible energy (a.k.a., the Aufbau principle) H 1𝑠 H 2𝑠 (Big idea #4) No two electrons can have the same set of 4 QN’s (Pauli exclusion) (Little idea #5) Electrons can shield each other from feeling the full nuclear charge (Little idea #6) Hund’s Rule: Electrons in different AOs are H 1𝑠 more stable when their spins are the same (parallel). He! 1𝑠 1 First ionization energy of first two periods 2 1 Two of lithium’s electrons are 1s 3 2s portion of Li 1s22s electron cloud 4 2 2s outer loop of Li 1s22s electron cloud 5 2s outer loop is shielded by 1s2 cloud 6 3 2s inner loop of Li 1s22s electron cloud 7 2s inner loop is not shielded by 1s2 cloud 8 4 2p portion of Li 1s22p electron cloud 9 2p is shielded by 1s2 cloud 10 5 CH101 - Multi-electron atoms handout Shielding of 2p 11 First ionization energy, I1 Big take-away messages: • Biggest effect is number of loops (n) • Then we look at the nuclear charge In general, increasing Z leads to larger Zeff and higher ionization energy Small things: • First new shielding (i.e., new subshell) decreases IE • First electron/electron repulsion decreases IE TRENDS: (a) Size and (b) Ionization energyà ALL FOLLOW ABOVE RULES! En = –(2.18 aJ) Zeff2/n2 radius = 52.9 pm n2/Zeff2 12 6 Periodic Trends summary Valence electrons are the ones with the largest value of “n” (number of loops) à easiest to ionize and largest in size Trends: (1) Down family à increase n, so decrease in ionization energy (also explains why alkali metals are the lowest ionization energy) (2) Across period à increase Z leads to increase Zeff and so increase in ionization energy (explains why the noble gases are the highest ionization energies) (3) Small “blips” across period à shielding and e-/e- repulsion 13 7