Inorganic - orbital energy

Question 1

what determines how well AOs combine?

Answer 1

symmetry
energy match
degree of overlap

Question 2

why do elements in the same group have similar properties?

Answer 2

properties are determined by the number, orbitals and energies of valence electrons
groups alined according to #valence e

Question 3

what is the Madelung rule?

Answer 3

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)

Question 4

five factors contributing to the energy of orbitals

Answer 4

1. screening
2. penetration
3. d,f-block contractions
4. relativistic effects
5. exchange interaction

Question 5

equation for orbital energy

Answer 5

E = -R(H) * Z(eff)^2/n^2

essentially depends on two variables: effective nuclear charge and principal quantum number

Question 6

two primary influences on Z(eff)

Answer 6

electron-nucleus attraction
electron-electron repulsion

Question 7

explain how screening impacts orbital energy

Answer 7

a completed shell screens very well (resulting in similar starting point for each new period)

Question 8

explain how penetration impacts orbital energy

Answer 8

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Question 9

what are d and f block contractions? how do they impact the energy of orbitals?

Answer 9

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Question 10

what are relativistic effects and how do they affect orbital energies?

Question 11

explain how exchange interactions affect the energy of orbitals

Answer 11

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Question 12

trends in Zeff

Answer 12

increases down the table (core e- don’t make a perfect screen)
increases from left to right due to imperfect screening

Question 13

Slater’s rules overall equation

Answer 13

Zeff = Z - S
Z is actual nuclear charge
S is a screening constant

Question 14

how is Slater’s S determined ?

Answer 14

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

Question 15

assumptions for Slater’s rules

Answer 15

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

Question 16

define ionisation energy

Answer 16

the energy change for removing e- from one gaseous mole of atoms to form one gaseous mol cations

Question 17

what is Koopman’s theorem? explain why ionisation energy is not exactly equal to orbital energy

Answer 17

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

Question 18

main difference between ionisation energy trend and orbital energy

Answer 18

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

Question 20

what does the standard half-cell potential / potential for reduction for an element show?

Answer 20

shows reduction of an ion in its group oxidation state to the element, or reduction of the element to a (poly)anion

Question 21

main trends in standard half cell potential

Answer 21

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)

Question 22

why do heavier elements prefer oxidation state of group # - 12
rather than 10?

Answer 22

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

Question 23

define electronegativity

Answer 23

the tendency of an element to attract e- to itself
basically a one number summary of the energy match of a bonding interaction

Question 24

how is X(Allen) calculated?

Answer 24

weighted average of energies of valence orbitals, using experimental ionisation energy values for each of the valence s and p orbitals

Question 25

what does the Pauling electronegativity take into consideration?

Answer 25

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

Question 26

what does a van arkel diagram show?

Answer 26

triangle diagram for binary compounds of s and p block atoms, showing ∆X (“energy match”) vs X(avg)

Question 27

define oxidation number and state

Answer 27

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

Question 28

rules for finding oxidation number

Answer 28

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

Question 29

highest possible positive oxidation state
and outliers

Answer 29

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-

Question 30

explain oxidation numbers of H

Answer 30

+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)

Question 31

what are electride solutions?

Answer 31

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