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(2) Main Group Chemistry > Group 14 > Flashcards

Group 14 Flashcards

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1
Q

What is the outer electron configuration?

A

ns2np2

There are 4 valence electrons

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2
Q

In what way does this group show the greatest variation?

A

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

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3
Q

What is the range of oxidation states?

A

They range from +4 in the dioxides and tetra halides and -4 in the hydrides

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4
Q

Does group 14 show the inert pair effect?

A

Yes as the +4 oxidation state becomes less important with respect to the +2 oxidation state as the group is descended

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5
Q

Why does catenation become less important as the group is descended?

A

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

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6
Q

Why are multiple bonds stable for carbon but rarer for the heavier elements?

A

This is because pi bonds and pi overlap is distance sensitive

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7
Q

What is the structure of the majority of compounds?

A

EX4

For Sn and Pb the inert pair effect occurs and we see stable EX2 compounds

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8
Q

Describe the trend in ionisation energy

A

There is a decrease due to increase in shells and shielding and so lower zeff

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9
Q

Why is there an anomalous increase in ionisation energy at Ge and Pb?

A

There is an increase due to poor d shell shielding as increased zeff

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10
Q

What is an isoelectronic relationship?

A

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

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11
Q

Describe the structure and properties of diamond

A

Composed of sp3 hybridised carbons
3D covalent network
Second hardest material
Electrically insulating as there is no delocalised pi system

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12
Q

Describe the structure and properties of graphite

A

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

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13
Q

What is C60?

A

A fullerene

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14
Q

What are carbon nanotubes?

A

Rolled up graphene sheet

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15
Q

What compound is silicon similar to?

A

Diamond

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16
Q

Why is Si=Si unstable?

A

Silicon is a large atom and so overlaps are poorer

17
Q

What is meant by isolobal?

A

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.

18
Q

What is B-N isolobal with?

A

It is isolobal with C-C.
This means is has a similar structure
There is a difference in the bond polarities

19
Q

What are the properties of cubic nitride?

A

Similar to diamond
Hard
Stable
Electrical insulator

20
Q

What are the properties and structure of hexagonal boron nitride?

A 
Similar to graphite 
Reduced pi delocalisation 
Stronger bonds between the layers 
Hard
Direct stacking
21
Q

What are hypervalent compounds?

A

These are compounds that contain more than 8 electrons in its valence shell

22
Q

Which orbital is involved when SiCl4 reacts with water?

A

A sigma antibonding orbital accepts the lone pair of electrons from the water

23
Q

Why can SiCl4 react with water and be a Lewis acid but CCl4 cannot?

A

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

24
Q

Describe the geometry and polarity of CX4

A

It is covalent and tetrahedral

Overall it is non polar as the cx polar bond cancels out overall

25
Q

Describe and explain the trend in stability of CX4

A

The stability decreases as the halogen atom becomes larger

This is because the CX bond enthalpy decreases due to the reduction in orbital overlap

26
Q

Describe the trend in acidity of SiX4?

A

This follows the trend in electronegativity

SiF4> SiCl4 > SiBr4 > SiI4

(2) Main Group Chemistry (11 decks)

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