Izod lectures 1-3 Flashcards
(52 cards)
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 higher n, 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.
What does electronegativity depends on
depends on the oxidation state and substituents
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 than In as there are 14 4f electrons before Tl. 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 the trend in homonuclear single bond energies down a group and why this is the case
Homonuclear single bond energies decrease down a group, the E-E bonds become weaker as there is an increased number of shells. The orbitals become larger and more diffuse so 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 effective nuclear charge the orbitals are more contacted therefore 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 the fact phosphorus has a lone pair, therefore lone pair lone pair repulsion for P hence weaker bond
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
What oxidation states can group one possess
+1
what oxidation states can group 2 possess
+2
What oxidation states can group 13 possess
+3 and +1
