Chemistry of the elements L4/5 Flashcards
Describe covalent trend going down group for s-block elements
Size of atom increases down group because even though Zeff increases so does n and n dominates
S block elements show regular increase of 0.2-0.5 A
What is the group 13 anomaly?
The expected expansion in size is seen from B to Al
Ga is the same size as Al and there is only a small size increase Ga–> Tl
This is because d-block contraction of ~0.3 A occurs because 10 elements have been encountered so Zeff is higher
At Tl there is f- and d-block contraction and relativistic effects and thus Tl is the same size as Na
(NB: Tl+ is poison because disrupts Na+ metabolism)
Why are 4d and 5d transition metals the same size within each group?
F- block contraction (so 5d not bigger than 4d as expected)
Also relativistic contraction of 6s which is valence orbital
Define ionisation energy
The enthalpy change when one mole of atoms/ions in the gaseous state is oxidised by 1e-
What are overall IE trends across period and down group?
Period- increased bc of Zeff
Group- n dominates, e- further from nucleus and easier to remove, decreases
What happens when element has half full/ full electron configuration?
Takes more energy to remove outermost electron hence spikes in IE vs n graph
Why are O, Ne and F below the trend line?
Quantum mechanical exchange energy, atoms prefer not to have pairing of electrons with opposite spins
Electron Affinity define
Energy released when one mole gaseous atoms/ions is combined with 1 mole electrons
Defined as positive if exothermic, negative if endothermic
Why are all values usually positive?
Because values are a balance between Zeff (attraction approaching electron feels) and repulsion of e- cloud and Zeff usually wins
What is overall EA trend across period?
Increase due to increased Zeff
Why is there a high value for Au?
Relativistic effects, Au- 5d10 6s2 v contracted
NB: remember from A level Au is s1 d10
What is electronegativity?
Ability of an atom to attract electrons to itself within a molecule (NOT thermodynamic)
Draw MO diagram to explain why electronegative atom becomes d-
(see notes for diagram)
What did Pauling notice?
That the experimental value for heteronclear AB bond energy is higher than homoatomic AA/BB
E(AB)=? in kJmol-1
1/2(E(aa)+E(bb)) + 96.5(chi(a)-chi(b))^2
What is borderline of Pualing scale between ionic and covalent?
Difference in electronegativity of 1.8
Draw a van Arkel-Ketalar diagram
(see notes for diagram)
What does the low electronegativity of metal elements result in?
Higher energy, more diffuse orbitals and a tendency to delocalise e- in classic metallic structure (therefore drift to metallic character down the periodic table)
High electronegativity if non-metals…
Leads to lower energy, more compact orbitals and tendency to localise e- in 2e- bonds (therefore there is a drift to covalent character across the periodic table)
Why is there a maintenance of covalent character in group 13 compared to s-block?
Added shielding effect overwhelmed by d/f-block contraction and Relativistic Effects
Why 4p,5p,6p higher ionisation energy than expected?
4p,5p,6p higher IE than expected due to d-block contraction so harder to take off electron because orbital energy lowered
