Melting points generally increase going from sodium to silicon, then decrease going to argon.Boiling points generally increase going from sodium to aluminium, then decrease to argon .


Sodium, magnesium and aluminium are all metals. They have metallic bonding, in which positive metal ions are attracted to delocalised electrons. Going from sodium to aluminium:

* the charge on the metal ions increases from +1 to +3 (with magnesium at +2) ...
* the number of delocalised electrons increases ...
* so the strength of the metallic bonding increases and ...
* the melting points and boiling points increase.


Silicon is a metalloid (an element with some of the properties of metals and some of the properties of non-metals). Silicon has giant covalent bonding. It has a giant lattice structure similar to that of diamond, in which each silicon atom is covalently-bonded to four other silicon atoms in a tetrahedral arrangement. This extends in three dimensions to form a giant molecule or macromolecule.

Silicon has a very high melting point and boiling point because:

* all the silicon atoms are held together by strong covalent bonds ...
* which need a very large amount of energy to be broken.


These are all non-metals, and they exist as small, separate molecules. Phosphorus, sulphur and chlorine exist as simple molecules, with strong covalent bonds between their atoms. Argon exists as separate atoms (it is monatomic).

Their melting and boiling points are very low because:

* when these four substances melt or boil, it is the van der Waals’ forces between the molecules which are broken ...
* which are very weak bonds ...
* so little energy is needed to overcome them.

Sulphur has a higher melting point and boiling point than the other three because:

* phosphorus exists as P4 molecules ...
* sulphur exists as S8 molecules ...
* chlorine exists as Cl2 molecules ...
* argon exists individual Ar atoms ...
* the strength of the van der Waals’ forces decreases as the size of the molecule decreases ...

Been decades since ...

O, apologies to the teachers since I didn't update my chemistry blog for ages ( didn't even know that it existed if not to be reminded by someone ). Ok back to business.




So I can say i did fairly good for my written paper since for the mock examination i scored 13/45 but this time round for the promos, i got 36/80. which is an E but :D yea vast difference but i still believe there's room for some improvement. Regretting the fact that I didn't take my homework seriously and almost failed chemistry due to that reason. Yeap more difficult/brain-teasing topics up ahead so, gotta work extra harder.




When the new terms starts we were exposed to 2 new topics so far, Ideal Gas and Energetics. For the topic Ideal Gas, some definitions and understandings are required such as, assumption that the collisions between gas particles are elastic. And the most important formula Pv = NRT. Other than that it's either applications of the formula into questions or the sketching of graphs when comparing different units of the formula. Another memorizing topic since I can't find any understanding in it. Energetics, even the name is self described how hard the topic's going to be, but luckily its linked to our previous o-level topic ( Endo/Exothermic energy ). So far TanDude and Miss.Jee are drilling the basic foundations of the topic in our brains so that when we are approaching the topic it be much more easier for us. Basically we are required to memorize what type of Enthalpy(heat content) change the reaction is and its accompanying chemical equation with state symbols. For example Standard Enthalphy change of Neutralization -> NaOH + HCl -> NaCl + H20. So basically I'm trying to point out that things are going to get even more difficult that before and we don't really have any more time to be fooling around. So guys let's dig our grave in advance :D




Peace,
Kensei.