Group 14 Flashcards
(26 cards)
What is the outer electron configuration?
ns2np2
There are 4 valence electrons
In what way does this group show the greatest variation?
Carbon behaves as a non metallic element forming covalent compounds with other non metals
They also form structures with high ionic character with electropositive metals
What is the range of oxidation states?
They range from +4 in the dioxides and tetra halides and -4 in the hydrides
Does group 14 show the inert pair effect?
Yes as the +4 oxidation state becomes less important with respect to the +2 oxidation state as the group is descended
Why does catenation become less important as the group is descended?
This is due to the decreasing bond enthalpies of the X-X bonds and partly because the heavier atoms are larger and have orbitals that are less available for reaction
Why are multiple bonds stable for carbon but rarer for the heavier elements?
This is because pi bonds and pi overlap is distance sensitive
What is the structure of the majority of compounds?
EX4
For Sn and Pb the inert pair effect occurs and we see stable EX2 compounds
Describe the trend in ionisation energy
There is a decrease due to increase in shells and shielding and so lower zeff
Why is there an anomalous increase in ionisation energy at Ge and Pb?
There is an increase due to poor d shell shielding as increased zeff
What is an isoelectronic relationship?
If two molecules have the same number of electrons or the same electronic configuration, they are said to be isoelectronic
This leads to similar chemistry
Describe the structure and properties of diamond
Composed of sp3 hybridised carbons
3D covalent network
Second hardest material
Electrically insulating as there is no delocalised pi system
Describe the structure and properties of graphite
Consists of sp2 hybridised carbons
Bonding within the sheets are strong but weaker bonds between the sheets
Graphite is soft
Electrically conducting due to overlap of pi orbitals creating a delocalised system
Offset sheets
What is C60?
A fullerene
What are carbon nanotubes?
Rolled up graphene sheet
What compound is silicon similar to?
Diamond
Why is Si=Si unstable?
Silicon is a large atom and so overlaps are poorer
What is meant by isolobal?
Two fragments are isolobal if the number, symmetry properties, approximate energy, and shape of the frontier orbitals and the number of electrons in them are similar.
What is B-N isolobal with?
It is isolobal with C-C.
This means is has a similar structure
There is a difference in the bond polarities
What are the properties of cubic nitride?
Similar to diamond
Hard
Stable
Electrical insulator
What are the properties and structure of hexagonal boron nitride?
Similar to graphite Reduced pi delocalisation Stronger bonds between the layers Hard Direct stacking
What are hypervalent compounds?
These are compounds that contain more than 8 electrons in its valence shell
Which orbital is involved when SiCl4 reacts with water?
A sigma antibonding orbital accepts the lone pair of electrons from the water
Why can SiCl4 react with water and be a Lewis acid but CCl4 cannot?
C had a higher Ea than S
Silicon is larger and so can have more than four groups around it- it is more exposed to attack
Carbon is small and cannot as it is more sterically shielded
The sigma antibonding orbital which accepts the lone pair is higher in energy in C than it is in Si
Describe the geometry and polarity of CX4
It is covalent and tetrahedral
Overall it is non polar as the cx polar bond cancels out overall
