Guide to Crapping in Your Chemistry Test

=================================================
==========Guide to Crapping in Your Chemistry Test=========
========================Part 1=====================
=================================================

Version 1.0
Last updated 30/1/09
Author: Sunny Ooi Jian Zhen


Intro:
This guide is made in the hopes of helping those hu cant pass their chem, or lack confidence.

This guide SHOULD not be made your primary hope in the exam, coz. as the name suggest, its crap.

This guide should only prove useful when one does not know how to answer the question and has to crap, so the methods here may sound like crap to those who are able to answer the question.

Please dun flame. T_T

============================================================

1. Inorganic Chemistry

Important things to note here is the electron configuration, equations n explaining stuff.

I advice to reali noe the configuration stuff, coz tat can probali help u to do all the explaining.


So first part of my guide is how to crap for the explaining part.





=======================================================
================Explaining Stuff===========
=======================================================



There can be 3 cases when facing a problem that requires u to explain why;
i) Noe.
ii) Dunoe.
iii) Never see b4.

First case, sure pass.
2nd case, got hope.
3rd case, pray hard.

BUT have no fear, hopefully after tis can pass la. =P

** FOr explainling type questions, ALWAYS, ALWAYS Write a summary or conclusion at the end



Sample question.

"The first ionizing energy of phosphorus is higher than sulphur. Explain why."
question from chem january 08 UTAR paper. lazy type out all so it may seem a little different.

For this question, i like to call it a "Exception Type" question. This is because it ask u why an exception is present.

So for those hu are grouped in the "Never See Before" group, u gotta learn how to see wat type of question it is.

Chances tat questions tat have the explain why, why, reason etc etc in the question is the exception type questions.

So how do you answer an "Exception Type" question?

Step 1

You have at least noe how to do electron configurations.

"Exception Type" questions for UTAR syllabus only have 2 major exceptions.

i) Stability of the Electron Shells
ii) Fluoride atom


============================
Stability of the Electron Shells
============================


Again, u have to at least noe hund's rule tat says tat electrons filled up half filled is more stable. (at least i tink its hund's rule). but nwayz try writing out the electron configuration of the atoms. You should see some Special stuf about them




As u can see, the 3p shell of phosphorus is half filled which means it more stable than sulphur.

Tadah. Try tis technique when u come across this type of questions. Draw out the electron configuration.





Another thing u have to noe is the 4s n 3d orbitals , the energy level between them is low.

In simple terms, means the electron can jump jump from 4s to 3d, see they syok which wan.

The electron will jump to make the atom more stable. This is mostly related to Transition elements.

Sample question.

"Write the electron configuration for Chromium (Cr) and Copper (Cu)"

Copper:

As u can see, the lower wan has half filled electrons in its 3d orbital, which is more stabil, so the 2nd configuration is taken, not the first.





Chromium:


The second arrangement has the 3d orbital fully filled, means its more stable.








====================================================================

Florine atom

=====================================================================

Florine actuali very simple.. florine very SMALL. so usuali the bond length between it and another atom very short. So it very hard react. End of story. =P


(31/01/09)

**bond length is from the middle to middle.



But thats not all for the special fluorine. Fluorine is a very very very VERY VERY electronegative atom, means it has a very high tendency to attract electrons. Mostly the question has a relation to its electronegativity.

So what if its very electronegative, big deal.

Wrong, its a big deal. Bcoz its so electronegative, it can form hydrogen bonds.

Hydrogen bonds is bonds formed between [H]ydrogen and a very electronegative atom, such as F,O and N.

You have to remember tat hydrogen bonds can be formed by [F]luorine, [O]xygen and [N]itrogen, Very important in the organic chem.



Sample question.

"Explain why the boiling point of hydrogen fluoride is the higher than the boiling point of hydrogen chloride."

-question from UTAR april 2008-

So u should be able to explain it alreadi rite? but jz in case, heres wat i would write.

-fluorine is a very electronegative atom
-can form hydrogen bond between H and F
-need more energy to break the bonds. (Van Der Waals and hydrogen bond)
(summary!)
-hence, HF has a higher boiling point than HCl

=====================================================================

Ok, so we r done wif electron arrangement, so lets go to other stuff they may ask. Boiling point, acidity, etc etc.

Here's a summary.

Boiling point	Van der Waals forces, Hydrogen bonds
Acidity	Ability to dissociate H
Basicity	Ability to accept H

So if it comes out in test, n u have no idea y, jz crap some stuff using those words. =D

Should be can get a few marks la. hehe.



===================================================================
Organic Chem
===================================================================

This wan go many, n if i write them out, it wont be a guide to crap ledi. (n im lazy =P)

So i jz gonna tell the basics, after tat u gotta crap on ur own. =P



Boiling point

i) ALWAYZ FIND THE HYDROGEN BOND. Mostly questions will ask about it.


Sample question.

"Why does carboxylic acid have a higher boiling point than amines and alkenes?"

So, basics u gotta noe is wat are those stuff.

Carboxylic acid got -COOH
Amine got -NH2
Alkene got - Double bond.


So, if u have been paying attention, u would have realised smt.

Boiling point question. Wat should u do first?

Find the hydrogen bond if any.






Carboxylic acid- hydrogen bond formed wif O and H

Amine- hydrogen bond formed wif N and H

Alkene- none.



So, now u should be able to explain why caboxylic acids and amines have a higher boiling point.

BUT!
Why carboxylic acid higher? ><"

If u tink about it, wat makes a hydrogen bond stronger?

Imagine 2 magnet, with a positive and negative pole each being brought near each other. I

f the magnet has a stronger negative pole, the attraction stronger rite?

So in hydrogen bond cases, its similar.

If the electronegative atom is more electronegative, (meaning its very easy to attract electrons) the stronger the hydrogen bond.

=) Get it?

So sample answer mayb smt liddat.

-carboxylic acid and amine has hydrogen bonds while alkenes onli have weak van der waals forces.

-more energy needed to break the hydrogen bonds
-higher boiling point.

-the hydrogen bonds of carboxylic acid is stronger than amine.
-tis is because the hydrogen bonds formed between H and O is stronger than H and N
-tis is because O is more electronegative than N

-hence, more energy is needed to break the hydrogen bonds of carboxylic acid
-which makes it have the highest boiling point.

(summary)
- Carboxylic acid has the highest boiling point, followed by amine and lastly alkenes. ============================
Electron donating/withdrawing Groups
============================

Tis is a quite popular question.


Electron donating groups are groups tat PUSH their electron while
electron withdrawing group PULL electrons.

Electron donating group

1. R(alkyl groups)

For tis case rite, the C will have a higher negative charge, cause the R all push towards C.

So the C will have a partial negative n H will have a partial positive

The force between them bcome stronger, coz C bcome more negative.

Remember the magnet. =D

Electron withdrawing group

1. Benzene ring
2. Halogen

Tis case on the other hand, the H easy to release.

As the electrons are being pulled away from the C, the Partial negative of the C bcom less,

So strength between H and C bcome weaker

H easier to go out/dissociate.







U can use tis basics to answer most questions. Like acidity and basicity. =)

Good luck ya.


==========
End of part 1.
==========