Ch2b Flashcards
When does the Shrodinger equation fail?
Not possible for atoms with more than one e-.
What is Orbital Approximation used for? What does it take into account?
- Used for atoms with more than one e-, assign hydrogen-like orbital modified by the effect of other e-s of the atom.
- It takes into account average electric field fue to other e-s, and magnetic moment associated with their orbital motion and spin.
Define Pauli Exclusion Principle, Aufbau principle, and Hunds rule of maximum multiplicity and Pauli Principle
- Pauli Ex: each e- is described by a unique set of 4 quantum numbers.
- Aufbau: to obtain gs configuration, e-s added to lowest available energy first.
- Hunds rule: for degenerate orbitals, e-s are added with parallel spins one orbital at a time until sub shell is half-filled, thus maximizing unpaired spins.
- Paul pr: maximum 2- per orbital.
Why do we follow Hunds Rule?
Pairing energy is unfavorable, because it increases electrostatic repulsion between two e-s placed in the same orbital. Exchange energy is favorable, stabilizing quantum mechanical effect resulting from exchanging pairs of e-s with parallel spins in the same sub shell to achieve the same net arrangement as before.
What is unique about TMs e- configuration?
- for stable cations and anions of tm’s, always leave remaining valence e-s in d subshell.
What tendency regarding e- configuration do TMs have?
empty s-subshell tendency, because s orbital is higher in energy than 3 orbital.
What are the crossover points where s & d have the same E, for tms (charge: 0,+1,+2)?
- M(0): s E below d for 1st few metals
- M(+1): s E above d for most metals
- M(+2): s E above d for all metals
Describe the valence e-s of TM ions with over or equal to +2 nuclear charge
They only have d e-s in their valence shell.
Why is the 1s2 2s2 state of Li lower in energy than the 1s2 2p1 state?
in the 2s, the e- penetrates closer to the nucleus than the 2p, thus feels higher nuclear charge.
Effective nuclear charge felt by an e- is less than the real nuclear charge dues to shielding of other e-s charge density (T/F)
True
What is the importance of shielding?
- shows how strongly e-s are attached to the nucleus.
- explains why orbitals differ in energies.
- is the cause of electromagnetically differences of elements.
What is the difference between a small and large effective nuclear charge on e-?
Small Z* felt by valence e- indicates weak attraction to the nucleus, thus can be easily removed because low IE.
Large Z* felt by valence e- indicates strong attraction to the nucleus, hard to remove because high IE, and not a highly electronegative atom.
Effective nuclear charge trends in periodic table
increases across a row and decreases down a column due to orbital size.
Define Clementi and Raimondi Rules
better at estimating the effective nuclear charge by computational methods, values are usually provided by a table.
