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HOMEWORK:
- Revise atomic spectra
- Absorption and emissions spectra
- Structure of an atom
Diamond vs Graphite:
- Diamond:
- In diamond, covalent lattices come from Carbon bonding in a tetrahedral shape.
- 4 covalent bonds per carbon atom
- $\therefore$ no delocalised electrons or any other charged particles(ions).
- Molecular network
- (no weak intermolecular forces)
- Thus, diamond has very high melting point.
- Does not dissolve in water/organic substances
- Not electrically/thermally conductive
- Graphite:
-
3 covalent bonds per carbon atom
-
1 electron becomes delocalised
-
Molecular network, layered
-
Weak intermolecular forces between the layers of graphite
-
Still high melting/boiling point, you're still separating the strong covalent bonds (lower than diamond. breaking 3 vs 4)
-
Electrically conductive, not as conductive as metals, however.
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Soft: you can take the layers, and squash it.
-
Does not dissolve in water, or organic solvents.
- Why? You need to separate all atoms at the same time, and its not easy to break the many covalent bonds.
-
Can be used as a lubricant
Intermolecular - between molecules (doesn't apply to diamond, it is one big molecule)(discrete molecules)
Intramolecular - inside a molecule, i.e. a covalent bond
When you heat up something, (i.e. melting/boiling point), you do not break intramolecular forces, but intermolecular forces.
e.g. $H_2O_{(s)} \rightarrow H_2O_{(l)} \rightarrow H_2O_{(g)}$
Not $H_2O_{(l)} \rightarrow H_{2(g)} + O_{2(g)}$ , this is explosive
Thermal conductivity refers to the kinetic energy of a substance's atoms/molecules.
Buckminsterfullerene - $C_{60}$
- Will conduct in particular circumstances
- Such as in impurities (mixed with other substances)
- Can be used as a lubricant
- Weak van der Waals forces only
- Black/brown solid is a soft powder
- Sublimes at 800k
- Semiconductor in pure form
Elements of Period 3:
- Na - M, N
- Mg - M, N
- Al - M, N
- Si - C, MN
- $P_4$ - C, SM
- $S_8$ - C, SM
- $Cl_2$ - C, SM
- Ar - N/A
Variation in melting points across period 3:
- Increases to silicon (very high in comparison to the increase for metals), gets lower and lower from silicon (steep fall)
Electrical conductivity:
- All metals are very electrically conductive, due to sea of delocalised electrons
- Silicon - can only be electrically conductive if in impurities
- Simple molecules - they have no delocalised electrons or charged particles (ions) that move around, therefore zero electrical conductivity.
