Izod lectures 1-3 Flashcards
Define effective nuclear charge (Z*)
the net positive charge experienced by an electron in a many-electron atom
Describe how effective nuclear charge changes across a period
across a period effective nuclear charge increases due to incomplete shielding by inner electrons
Describe how effective nuclear charge changes down a group
Down a group effective nuclear charge increases but electrons are in higher principle quantum number shells so they are further from the nucleus
Describe how covalent radius changes across a period
across a period covalent radii decreases as there is a higher effective nuclear charge and therefore the the electrons are held more tightly and the orbitals are contracted
Describe how covalent radii changes down a group
down a group covalent radii increases, although effective nuclear charge increases there are more nuclear shells, the increase in shells outweighs the increase in Z*
Why is the covalent radii for aluminium the same for the covalent radii of gallium
Before filling up 4p we fill up the 3d orbitals, so there are 10 more d electrons added between Ca and Ga, therefore higher Z* decreases covalent radius for Ga. Z* experienced by Ga valence electrons is much greater - valence orbitals contracted therefore a smaller covalent radius
Known as the D block contraction
Describe why indium almost has the same sized covalent radius as Thallium
In (indium) is also affected by d block contraction but the number of shells increases so covalent radii increases. Between In and Tl there is the F block which has 14 electrons. 4f electrons are very poor at shielding therefore the orbitals contract. Lanthanides contraction
Tl has a smaller covalent radius than expected
Define electronegativity
electronegativity is the ability for an atom to attract electron density towards itself in a molecule
How is electronegativity measured
electronegativity cannot be measured directly instead they are calculated using the Pauling scale
Describe the trend in electronegativity down a group
going down a group electronegativity decreases because there is an increased number of electron shells therefore greater shielding so it is harder for the nucleus to attract electrons
Describe the trend in electronegativity across a period
as we move across the period, the effective nuclear charge increases and the atomic size decreases. Therefore, the tendency to attract electrons increases, thereby increasing electronegativity.
Why does gallium have a higher electronegativity than aluminium
Gallium has a higher electronegativity to aluminium - extra 10 3d electrons before Ga which increases the effective nuclear charge therefore an increase in electronegativity.
Why is the electronegativity for thallium larger than indium
electronegativity of Tl is also larger the In as there are 14 4f electrons before Hf. This increases the effective nuclear charge which increases electronegativity.
Define homonuclear single bond energy
the strength of a chemical bond between two identical atoms
Describe how the homonuclear single bond energies change down a group
down a group the E-E bonds become weaker down a group as there is an increased number of shells. The orbitals become larger and more diffuse to there is poorer orbital overlap and therefore weaker bonds
Describe the trend in homonuclear single bond energies going from Be-Be to C-C
from Be-Be to C-C bonds become stronger, due to an increased number of in effective nuclear charge the orbitals are more contacted therefor there is better orbital overlap
Is a N-N bond stronger or weaker than a C-C bond and why
N-N much weaker than C-C as nitrogen possesses a lone pair. There is therefore lone pair lone pair repulsion and therefore a weaker bond
Is an O-O bond stronger or weaker than a N-N bond and why
O-O bond is much weaker than a N-N bond as there is 2 lone pairs on each oxygen atom. There is also a small internuclear distance between the oxygen atoms to therefore they experience stronger repulsion and hence a weaker bond
Is an Si-Si bond stronger or weaker than C-C
Si-Si weaker than C-C. Si is larger so has more diffuse valence orbitals therefore poorer overlap and weaker bond
Is a Si-Si bond stronger or weaker than P-P
Si-Si is stronger than P-P due to lone pair lone pair repulsion for P
Is a N-N bond stronger or weaker than P-P
N-N is weaker than P-P, phosphorus is larger therefore lone pairs are further apart the lone pair lone pair repulsion much less for P than for N
Define polarising
the distortion of the electron cloud around an atom or molecule, often caused by the presence of a nearby charged species
Describe group 1
Ground state electron configuration []ns1. The ns1 electron is easily lost hence a +1 oxidation state. Bonding ionic
how is the chemistry of Li+ often different to other M+
li+ can react with N2 whereas other group 1 metals do not react with N2
6Li + N2 -> 2Li3N
What is the reaction when group 1 metal react will H2O
M + H2O -> M(OH) + 1/2 H2
Describe group 1 complexes
M+ are hard cation and favour hard donor ligands.
Has a low charge/radius ratio therefore are labile. Stability of complex decreases down a group.
More stable complexes are with polydentate/macrocyclic ligands
Describe the properties of organolithium reagents
- very polar bond C-Li
- very nucleophilic
- very basic
Describe the C-Li bond and BunLi reaction with water
C-Li very polar reacts with H2O and O2
BunLi + H2O -> BunH + LiOH
Must be handled under inert atmosphere (N2,Ar)
Describe the trend in R-M bond where M is group one metal
M more electropositive down group. M-C bond therefore more polar and hence more reactive
Generally describe group 2 metals
ground state electron configuration []ns2. +2 oxidation state only
Describe beryllium
highly toxic
Very small atom and the chemistry is very different to the rest of the group. Valence shell electrons experience high Z*, bonding much more covalent
Describe beryllium complexes
almost always Be2+ is 4 coordinate, naked beryllium is not observed observed but complexes are stable.
[Be(OH2)4]
Write the reaction of [Be(OH2)4]2+ and water and describe the resulting solution
Be2+ very polarising
[Be(OH2)4]+2 + H2O -> [Be(OH2)3(OH)]+ + H3O+
Acidic solution
Describe magnesium chemistry
magnesium compounds are more ionic than beryllium compounds. Mg2+ is a very small cation. Mg chem often similar to lithium chemistry
what is the reaction when magnesium reacts with N2
3Mg + N2 -> Mg3N2
Describe Ca,Sr and Ba
very large cations - low charge to radius ration therefore are bvery labile. M2+-L more polar and often more reactive
