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.

http://www.onemanga.com/Naruto/441/
( Watch Naru-tard own Pein )


http://www.onemanga.com/Bleach/351/
( Come on Kensei APPEAR ALREADY !! )


I know this has nothing to do with chemistry but its the weekends got to de-stress myself.

Removed all pictures in my recent posts due to the fact that Ms Jee is experiencing Pop-up advertisements. This blog feels dead/boring just like reading something out of a chemisty textbook. Forgot to mention that Orbital is a 3-D region* from my previous post. Currently going throught the notes we printed out ourselves because there is going to be a test on MOLE on Monday. Got to start memorising/understanding formulas and defination since I'm expecting 80% - 100% of the test to be Short-answer question rather than MCQs. Hund's rule is really helpful when it comes to the questions in tutorial 3. Yawns, off to sleep now.

Got this defination from Ashvin's blogspot very helpful.

Isotopic: Atoms, ions or molecules containing same number of protons.
Isotonic: Atoms, ions or molecules containing same number of neutrons.
Isoelectronic: Atoms, ions or molecules containing same number of electrons.

Aufbau principle
Electrons occupy orbitals of the lowest energy available.

Pauli Exclusion Principle
Each orbital can accommodate only two electrons whose spins are always opposite.

Hund's Rule
When electrons are added successively to a subshell, they occupy the orbitals singly first before pairing occurs.

I feel dead tired, just came home around 9.30. Today we learnt about Atoms in a much more deeper concept which is totally O.O to me. Shells and sub-shells are still fine by me since its still related to the electronic configuration that we learned in Secondary level but ORBITAL is totally a new concept that I need to grasp fast. If I'm not wrong this is what Mr.Tan said, "Orbital is the region whereby it is possible to indicate where the electrons are most likely to be found." Maybe he wrote that or said it, doesn't matter and Orbital can be divided in to s, p, d, and f.

Just printed my own set of notes and reading ahead and found more familiar stuff coming back to haunt us during our 3 years in M.I. Stuffs like bonding, but looking at the my thick notes, we're going in depth regarding the topic bonding. Something about Ionisation and determining/caculating the shape of a molecules scares the living crap out of me. Ok off to sleep.

Ok just stolen some notes from Jasmine's blog. I just wondered, why do I have friends that have similar names like Jazz ( BJ ), Jesslyn ( LPP), Jasmine ( Don't know her chinese name ). It's really going to be hard calling their nicknames like "Jazz", "Jess" and "Jas". Ok this is really ridiculous. Nevermind about that particular topic.

Here's something I stole from " Jasmine's " blog. And by the way I don't just steal any particular information from some TomDickHarry, in fact I steal quality bullcrap which by the way is from Wikipedia.

What Kensei learned.

The equivalence point, or stoichiometric point, of a chemical reaction occurs during a chemical titration when the amount of titrant added is equivalent, or equal, to the amount of analyte present in the sample.

Different methods to determine the equivalence point include:

pH indicator
This is a substance that changes colour in response to a chemical change. An acid-base indicator (e.g., phenolphthalein) changes colour depending on the pH. Redox indicators are also frequently used. A drop of indicator solution is added to the titration at the start; when the colour changes the endpoint has been reached, this is an approximation of the equivalence point.

pH meter
This is a potentiometer which uses an electrode whose potential depends on the amount of H+ ion present in the solution. (This is an example of an ion selective electrode. This allows the pH of the solution to be measured throughout the titration. At the equivalence point there will be a sudden change in the measured pH. It can be more accurate than the indicator method, and is very easily automated.

Color change
In some reactions, the solution changes colour without any added indicator. This is often seen in redox titrations, for instance, when the different oxidation states of the product and reactant produce different colours.

Precipitation
If the reaction forms a solid, then a precipitate will form during the titration. A classic example is the reaction between Ag+ and Cl- to form the very insoluble salt AgCl. Surprisingly, this usually makes it difficult to determine the endpoint precisely. As a result, precipitation titrations often have to be done as back titrations.

Wikipedia is really a pal when it comes to educational stuff which I include in news as well, do not underestimated the power of Wikipedia it will someday save your life like it did for mine which is particularly today. As compared to other people's blogs in 09s2 my blog is not that educational ot helpful to you my fellow classmate so feel free to comment me on the way I present my daily chemistry studies.

Ok for real.

This chemistry blog is for real people. Teachers are invading and reading Each and Everyone of our Post. It feels weird but that is the reason why this blog is created ( keep reminding myself ). Ok here I go.

Strength / Weakness in chemistry :

Apparently my only which makes it the most important strength in chemistry is how good I am with memorising big details and picturing them into smaller points. In other words, I'm very good at memorising stuff last minute which happends to be a very bad habit of mine I can't control well. I keep telling myself its time to change my POV of studying through thick skull of mine. At the same time this becomes my weakness. When I tend to do last minute studying I don't study as much as others who studied much earlier than me, this prove to be a very big dissadvantage to me. I won't say this is much of a strength but instead this is a very Big weakness of mine which has to change. In conclusion, I have no Strength in Chemistry but trying to build up one by putting aside my weakness and trying to change it to my advantage.



Comments on Feedbacks

Hi Mr Tan, I'm really sorry if this offends you but do I know you from chemistry class? Were you the teacher during our lesson in the chemistry lab the one with the specs or did I get the wrong person?

Ok equipped my blog with many things very unrelated to chemistry, hope Ms Jee allows it. The reason, to brighten up my blog just abit so it would not be so "Boring".

Only been my 3rd post. I've started comparing the old periodic table used in our Secondary schools days and now, so much different. There's alot more elements with decimals in their number of Atomic mass. So shocked. Ok I lied, I've not learned much in the holidays but revised on Secondary school basic Chemistry. Ok off to "Study".

Is it me or am I missing out something? Why is everyone writing out thier ambition/ I - wanna - be - when - I - grow - up . Is is part of our assignment? In that case I SHALL WRITE too.

I wanna be a Cook, want to know why? Because Food is everything, I want to explore the unexplored which others fail to do. So basically I plan be an "Art" Chef creating what is impossible in any average cuisine, by breaking normal boundaries of ordinary culinary skills and building new bonds between different culture's culinary skills and therefore creating a new style of cuisine of my own.