Inorganic - orbital energy Flashcards
what determines how well AOs combine?
symmetry
energy match
degree of overlap
why do elements in the same group have similar properties?
properties are determined by the number, orbitals and energies of valence electrons
groups alined according to #valence e
what is the Madelung rule?
describes the rough order in which orbitals are occupied
orbitals with a lower n+l value (principal + angular) is lower energy and filled before
if same n+l, then lower n value has lower energy
(filled in diagonal lines of same n+l value)
five factors contributing to the energy of orbitals
- screening
- penetration
- d,f-block contractions
- relativistic effects
- exchange interaction
equation for orbital energy
E = -R(H) * Z(eff)^2/n^2
essentially depends on two variables: effective nuclear charge and principal quantum number
two primary influences on Z(eff)
electron-nucleus attraction
electron-electron repulsion
explain how screening impacts orbital energy
a completed shell screens very well (resulting in similar starting point for each new period)
explain how penetration impacts orbital energy
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what are d and f block contractions? how do they impact the energy of orbitals?
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what are relativistic effects and how do they affect orbital energies?
explain how exchange interactions affect the energy of orbitals
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trends in Zeff
increases down the table (core e- don’t make a perfect screen)
increases from left to right due to imperfect screening
Slater’s rules overall equation
Zeff = Z - S
Z is actual nuclear charge
S is a screening constant
how is Slater’s S determined ?
for ordered groups (s,p separate from d,f):
ignore all groups to the right
0.35 for each e- in the same group. except 1s = 0.30
s,p: 0.85 for each e- in 1 level below, 1.00 for two or more levels below
d,f: 1.00 for all groups to the left
assumptions for Slater’s rules
e- in higher orbitals do not contribute to screening
same shell e- screen to some extent
e- in lower shells are quite good / perfect screens
define ionisation energy
the energy change for removing e- from one gaseous mole of atoms to form one gaseous mol cations
what is Koopman’s theorem? explain why ionisation energy is not exactly equal to orbital energy
Koopmans: orbital energy is approximately -ve Ionisation energy
IE measures the difference between energies of atom and ion - the higher charge in the ion changes the energies of all the orbitals relative to their values in the neutral atom
main difference between ionisation energy trend and orbital energy
due to differences in exchange energy -number of ways to choose a pair of parallel spin e- after losing an e-
eg. N three ways to choose, N+ only 1 way. O and F same #ways hence easier
what does the standard half-cell potential / potential for reduction for an element show?
shows reduction of an ion in its group oxidation state to the element, or reduction of the element to a (poly)anion
main trends in standard half cell potential
H is 0 (by definition)
G1 and G2 -ve values (spontaneous)
p block period 6 elements favourable to reduce bc e- go into low energy 6s AOs (relativistic effects)
why do heavier elements prefer oxidation state of group # - 12
rather than 10?
the inert pair effect:
particularly stable in these states due to low-energy 6s orbitals, e- here are less available, larger than usual gap w 6p means only the 6p are readily lost
define electronegativity
the tendency of an element to attract e- to itself
basically a one number summary of the energy match of a bonding interaction
how is X(Allen) calculated?
weighted average of energies of valence orbitals, using experimental ionisation energy values for each of the valence s and p orbitals
what does the Pauling electronegativity take into consideration?
that bonding has both ionic and covalent contributions
ie. E(A-B) = E(covalent) + E(ionic)
covalent part: geometric mean of ionisation energies
ionic: proportional to the square of difference in electronegtivities
what does a van arkel diagram show?
triangle diagram for binary compounds of s and p block atoms, showing ∆X (“energy match”) vs X(avg)
define oxidation number and state
number: charge of an atom in a molecule/ion in the hypothetical ionic structure
a formal way of accounting how e-s are distributed
state: ox number as a roman numeral
rules for finding oxidation number
num of all ox #s = overall charge
least e-neg – if G1/2 assign +1/+2
if not, most e-neg –> G16/16 = -2/-1
highest possible positive oxidation state
and outliers
highest possible when all valence e- are lost
not possible for O, F and noble gases bc low orbital energies prevent loss of maximal number of e-
explain oxidation numbers of H
+1: 1s orbital energy is high enough that it readily loses an e- to make H+ (most common)
-1: but also low enough that H- containing reagents are stable (eg. NaH strong base)
what are electride solutions?
G1 metals and Ca, Sr and Ba dissolve in NH3(l) to form a blue/bronze coloured solution that can be used as strong reducing agents
