The Chronicles Of 3 Little Pigs!

Another chronicle written by my sister.

Enjoy!

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The wolf which attacked the three little pigs had died from the fall off the chimney, but the story, or the chronicle of the 3 little pigs did not quite end there.

That fatal accident had created a huge stir-up and earned raved reports from the press. The proud wolves found that snub hard to stomach, and that incident had, to a certain extent, affected the operation of the local Bee Hiang Hiang store. Thanks-giving was round the corner, yet there was hardly any pig caught to serve as the main ingredient. The scarcity of pork made pessimists in the Wolf-Village turn to other food-alternatives, and many lived on a vegetarian diet.

This food crisis drove everyone in the Wolf-Village to desperation, and the wish for a sumptuous meal during the festive season brought the brains of Wolf-Village together, to stage a comeback. The review committee hired the well-learned Professor Wolff to conduct an independent review of that fatal accident. Analysis showed that the huff-puff method passed down from several generations before was obsolete and was no longer effective in toppling the brick houses built by the pigs. The R &D done by the pigs in Housing Development Authority (HDA) was indeed remarkable, and the suggestion made by Professor Wolff to solve this problem was to burn the brick house and force the pigs out of their sty.
He calculated that the brick house needed at least 100 000 kJ of energy to be completely engulf in fumes, and complete combustion of 1 mole of coal released approximately 100kJ of energy. The molecular mass of this special coal, coal W, designed by Professor Wolff, was 800.00g. Detailed calculations showed that 1000 mole of coal W was needed, which would weigh 6.023 x 10 23 x 800g x 1000 = 4.8184x10 29g.

As soon as the required amount of coal W was produced, everyone from the Wolf Village was mobilized to transport the coal. The Huff-Puff method was abandoned, but the transportation left everyone huffing and puffing. The target sty for the first attack to be launched was the sty built by the 3 little pigs who were responsible the many months of distress suffered by villagers in the Wolf Village.

It was by no means an accident that the 3 little pigs survived. Although the previous ordeal was a victory for them, they did not rest on their laurels but worked on improving the safety aspects of their estate. They knew that although their houses were “huff-puff-proof”, they were nevertheless not fire-proof and would engulf in flames should a fire break out.

The smart 3 little pigs had long designed a hot air balloon that could support the mass of the 3 of them should there be a fire. Careful calculations and experimentation showed that in order for the hot air balloon to support their weight as well as the necessary amount of coal for continual burning, 2400dm3 per second of hot air was needed. One mole of a specially-designed, fuel efficient coal, coal P could provide 1 mole of hot air, which is 24dm3 upon combustion.

Thus in order for the 3 of them to stay in the air for 1 hour, 60 x 60 x 100 = 360000 mole of coal P was necessary. The molecular mass of coal P is 600.00g. Thus the total mass of coal P required was 600 x 360000 = 216000000g. Wow!!!


The time was ripe when Professor Wolff saw strong wind blowing in the direction of Pansy Village, the village where the 3 little pigs stayed.

“Comrades! Start the fire! ” ordered Professor Wolff, as he sat a distance away from that brick house, sipping red wine, waiting for succulent pork to be served soon. Professor Wolff choked on his drink when he saw the roof of the brick house shoot-open, and the 3 little pigs flying-off with a smirk on their face in the hot air balloon! The sudden attack had failed to restore the reputation of the wolves being the most-capable animals in PW town (consisting of only Pansy and Wolf Village), but further undermines the standing of Wolf Village in PW town. My goodness!!!

It appeared that the coming Thanks Giving dinner in Wolf Village had no choice but to serve many salad dishes, and there was a real prospect that a vegetarian diet might stay for good.

by: xue yin ( another miss pang )

My sister and shana inspired me ( not shana's fault, so please don't blame her ) to offer one of my chem classes on a written assignment ' The Chronicles Of The Mole '.

Being a weak english person, I try my best to write an event regarding the mole.

Enjoy...

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Huai Ren was waiting outside the A & E. The police had notified him of Jenny’s accident.
After the operation, he was informed by the surgeon that Jenny had escaped death and would be transferred to intensive care unit.
Huai Ren entered the room. Accordingly, Jenny had sprained her neck and fractured her ribs due to the crash. The fractured ribs pierced through bronchiole and the doctor had to give her pain killers through injections. Jenny’s arms suffered from deep cuts due to the broken windscreen.
Huai Ren walked towards Jenny and lamented at her misfortunes.
She was not like this before, at least 1 year ago.
Jenny had suffered from post natal syndrome ; after her maternity leave, she needed to deal with the day-to-day operations of the company and these had proven too much for her. Her dad had suggested Huai Ren to take over the CEO position so as to lessen her duties. Recently, the company was faced with problems of cash flow. A large sum of funds was trapped in an acquisition project of a promising company’s shares.
Jenny insisted Huai Ren had misappropriated the company’s funds.
Huai Ren left the ward for he knew if she woke up, he would not be the person Jenny would want to see.
After visiting hours, someone entered Jenny’s ward.
He took out a syringe and held Jenny’s arm. With a swift movement, the hollow needle pierced through the skin and into the vein. 2.25mg/dm3 of Warfarin was injected into the bloodstream via the vein. He had done his calculations well. For every 13 kg of body weight, there is an equivalent amount of 1 litres of blood. So, Jenny would have around 4 litres of blood if she weighed 50 kg.
The maximum concentration of warfarin that her body could take should not exceed 5.0 mg per body of blood. Since concentration can be defined as amount of substance dissolved in 1 L, which is 5.0/ 4 = 1.25 mg/dm3. An overdose of warfarin will lead to bleed profusely as blood will not clot.
He could visualise the shock on the nurses’ faces when they saw her bleeding while doing their rounds the next morning. Blood would be oozing non stop from her cuts.

*******************************************************

ms pang:)

2005 SciChemistry MCQ

2005 MCQ
1) A * explanation *less dense means light, so we use the upward dispalcement method( see notes blog )
so, reject option B. B is for heavy gases ( downward displacement method )
option C is for insoluble gases.
2) C
* explanation *
when particles at 50'C ( liquid ) becomes 120'C ( gases ),the energy of the particles increases, the spacing between the particles becomes far apart and hence the attractive forces between the particles decreases.
3) C* explanation *81 is nucleon number ( proton + neutrons ) / atomic mass37 is proton number ( proton = electron )therefore, 81-37= 44 neutrons.
4) C* explanation *Element X has a valency of +1Element Y has a valency of -2
therefore, when you use the criss-cross method, the formula is X2Y1
5) D

* explanation *

Element Q has 4 valence electrons

---> group 4 ( since number of valece electrons = group number )

Hydrogen and chlorine are non-metals.

So, non-metal & non-metal = covalent compound.

properties of covalent compound = low melting point ( see notes blog )

6) D
* explanation *look at what is given to you: you have 0.3 moles of C3H8.to find volume of gaseous productsso, which is the product they want? from the question, there is CO2 and H2O?answer: look at the state symbols, CO2 is in (g) state!!!mole ratio of C3H8 : CO2 is 1: 3no. of moles ofC3H8 = 0.1,1unit = 0.1,3 units = 0.1X 3 = 0.3 moles(please dont be careless and choose option B!! we have only found CO2's mole, the question wants VOLUME ) so,using P.K.X fav sentence: 1 mole of any gas = 24 dm3 at r.t.p,so, 0.3 mole = 0.3 X 24 = 7.2 dm3
7) B
* explanation *
during the process of neutralization, the temperature will increase ( see notes blog )that is why options C and D are out!now, when neutralization finishes, the ecess alkali added will make the temperature of the solution back to room temperature. Hence a decreasing gradient.
8) B
option A: when a more concentrated acid is used, the gradient of the graph will be steeper instead of gentle because the rate of reaction is faster.option C: when fewer amounts of reactant is used, the amount of CO2 produced will be less. So, it will not reached the same level as graph 1.option D: when powdered reactant is used, speed of reaction should increase, instead of decrease!

9) B
* explanation *

option A, D are out because all potassium salts are soluble!

remember the K-N-N-Na theory.

option C is out. Potassium sulphate is a salt, not a base.

answer is potassium carbonate neutralises the acid.

10) C

* explanation *

when halogen is Y added to X and Z, there is no reaction, this means that Y is the least reactive.

so, down the group of 7, reactivity decreases, so, Br- is the least reactive.

so, Y = Br-

if X can displace Y and Z, then X is the most reactive.

so, X = Cl-

11) B
12) D
* explanation *option A: coke is not used to oxidised slag!! coke is used to burn to give carbon dioxide and carbon monoxide!

option B: limestone is used to decomposed to form calcium oxide and carbon dioxide.

the calcium oxide is used to neutralise slag.

option C: molten iron is heavier, so it is at the bottom, and not floats on the slag!

13) D

14) B

15) A ( see textbook for the uses of cracking )

16) A

* explanantion *

in the complete combustion of organic compounds, only carbon dioxide and water are formed.

17) D

18) C

* explanation *

only compounds with C=C bonds will decolourise aqueous brmine.

other C= structure will not decompose aqueous bromine.

19) C ( see textbook )

20) D* explanation *polyester = many units of ester group.
Terylene contains ester linkage.Nylon contains amide linkage.Poly(ethene) contains many units of ethene .Protein contains amide linkage.

Remedial Timeslots for 3E2 Pure Chemistry

Dear 3E2,

These are the timeslots for our InTeNsIvE TrAiNiNg PrOgRaMmE.

Please bring your stationaries, Five Year Series and Chemistry Textbook and File.
Venue: 3E2 classroom

16/06/08

Elements, Mixture and Compounds

Time: 11.15am to 12.45 pm

17/06/08

Structure of solids, Bonding

Time: 9am to 12 pm

18/06/08

Balancing Equations

Time: 2pm to 4 pm

Note:

I am having lessons for 4a,4e and 5a on 16th and 18th, so i cannot schedule your 'programme' eariler.

The lesson will end early if we finish our planned programme. Please do not be late for lessons.

miss pang :)

Reply to Germaine's Question : Is hydrogen a metal or non-metal

GERMAINE: hydrogen is metal or non metal?

My Reply: Hydrogen is a non-metal! However, it loses electrons to form H+ ions. ( so, i guess that is why Germaine will question its identity ).
The reason is it is more stable.

However, in tertiary levels ( JCs / Polys/Uni ), Hydrogen can also gain electrons, which is H- ions ( hydride ). There exist many metal compounds in which metal bonds with hydrogen and hydrogen gains ELECTRONS from metals. Such compounds are known as Metal Hydrides!

Thankfully, not in your syllabus!

ms pang :)

Reply to Mark's Question

Mark asked: ' i thought carbon-carbon is a quadriplet bond? and is in diamond, which is a giant colvent bonding. '

My reply to HJ's question was ' Are there any COMPOUNDS with carbon - carbon quadruple bond. '

Your comment was for diamond.

Firstly, diamond is made up by many many CARBON atoms joined together through covalent bonding. It DOES NOT have any other elements ( only carbon atoms ) in the composition of diamond. So, it is not the same as HJ's question as diamond is an element, not a compound.

Secondly, Quadruple bonds means one element shares 4 electrons with another element, and vice versa. Total 8 electrons within the 4 bonds.

For diamond, each carbon atom forms only one bond with another carbon atom. Which means each carbon atom forms 4 single bonds with 4 other carbon atoms!

ms pang:)
p/s: I am not taking a break.... was busy with the preparation for philippine's trip!

Reply to HJ's Question: Are there any compounds with quadriplet bond?

Hj: ms pang,is there such thing as quadriplet bond?

my reply: Should not have at your level. The maximum number of bonds between two atoms is only triple bond. eg:

dot and cross structure of nitrogen molecule

Structural formula ( read as ' N triple bond N ' )

As for the presences of quadruple bond... yes.... mainly in transition metal. Eg: Chromium.

I double check with miss wendy heng regarding HJ's question and I almost forgotten that in uni, we did manage to draw quadruple bond!!! ( many thanks to her ).

Just for your information... not in your secondary syllabus.....

chromium acetate

I edited this diagram so that you can see the quadruple bond easier... the original diagram is blur and show 5 bonds due to low resolutions.

I didnt draw these structures, i got it from this website:

(1) http://www.gcsescience.com/a25.htm ( nirogen molecule )

(2) wwwchem.uwimona.edu.jm:1104/courses/chromium.html ( chromium acetate )

p/s: is KING = Gareth? .. i assume HJ as 'hong jie'

ms pang :)

Chemistry Remedial For 4E1/4 Sci-Chemistry and 3E2 Pure Chemistry

Dear 4E1/4 and 3E2

In view of the upcoming MYE ( mid year exam )2008. There will be remedials for these days:

4E1/4 ( 3e2, be patient. Your timeslot is written below 4E .. so read on)

Our remedial will resumes from this saturday ( 26 april 08 ) onwards. Reason for cancelling the remedial on 19 april is due to real busy day of mine from morning.

The remedial will be conducted at only 1 slot: 10 am till 11.30am at AVA.

Target audience... 60 pax of you.

Topic: Chemical Analysis ( Cation/Anion)

This is a SUPER difficult and important topic ; this topic worths at least [5 mks ] in exam EVER YEAR without fail.

Since this topic needs alot of practice... we will continue with more practise for chemical analysis on 3 May 08. Same time, same venue.

You are advise to turn up for both sessions so you can have maximum exposure to this topic. Should you choose to attend only 1 of the above sessions, you may feel lost as practise is a continuation process.

3E2

Please inform your parents you have remedial.

Session 1- Revision: Structure of Atoms & Bonding ( 26 april 08 / 8.30-9.30/AVA )

Session 2- Revision: Formulas & Balancing Equation ( 3 may 08 / 8.30-9.30/AVA )

I will be going through FYS on 30 April. So all of you please stay back after your last paper. Have your lunch before our revision.

For administration purpose and monitoring of results, these are the pupils who attend sat remedial:

22 march 08

anas, michael, jason, yazid, cheryl, natasha, cheng hong, ronald

29 march 08

jessica, weifen, jolene, farid, anas, michael, jason, cheng hong, natasha, cheryl, jeffery

05 march 08

farid, jeffery, cheng hong, david, michael, anas, meiling, jolene, natasha, cheryl, jia min, yan ne, pei yee, weifen

__________________________________________________

The preparation for O-Level Exam is similarly to preparing for a Marathon.....

Before you run, you need to warm up. However, with 'conditioning your body' for the run, it is impossible to have a marathon because it may lead to sprains and you may not even complete the run!!!

Slow and steady wins the race.

cheers,

ms pang:)

Reply To Mark's Question: Why must we have UV light for free radical substitution.

My reply:

Firstly to have chlorine radical, i need to get it from chlorine molecule....

So, I need a minimum energy to break up my chlorine molecule to get chlorine radical....

ms pang :)

Reply To Mark's Question: Nobel Gases Group 8 or Group 18

Mark asked: ms pang, why is it we learn that nobel gas are grp 8 metals when they are grup 18? source: http://en.wikipedia.org/wiki/Noble_gases

my reply:

Indeed an interesting question!!!

But, let me make an amendment to your question...

Noble Gases are group X or group 0 non-metals.... not METALS.

Anyway, why wikipedia says group 18?

This is a new TERMINOLOGY....

Most scientist wanted to fit Transitions Metal into groups too... recall in our periodic table, transition metals are catagorise as a 'rectangular block' with no group......

So, after adding the transitions metal, we will have 18 groups hence noble gases become group 18!!!

Nonetheless, facts from websites cannot be trusted wholesomely..... unless it is some education (edu) or government (gov) websites..... such websites have more credibility.

ms pang :)

Reply To Hao Eng's Question: Does SO2 have double bonds?

Hao Eng asked: Does SO2 have double bonds between them?

My reply: Yes!

Both sulphur and oxygen has 6 electrons in their outermost shell. In order to have 8 electrons for oxygen atoms (octet structure ), sulphur needs to share 2 electrons with EACH oxygen.

Alas, then sulphur will have 10 electrons!!! Which is not octet structure!

In tertiary levels ( jc/poly/uni), sulphur can 'expand octet' which is a term refering to an atom that has more than 8 electrons in its outermost shell ...

A piece of good news. You are not expected to draw this structure for O-level Exam.....

ms pang :)

p/s: i didnt draw this diagram, i got it from this website:

http://www.btinternet.com/~chemistry.diagrams/molecular_diagrams.htm

Reply To Qi Ying's Question: How many bonds does chlorine and hydrogen have?

Qi Ying asked: how many bonds does chlorine and hydrogen have?

my reply:

Chlorine and hydrogen does not have bonds. The question 'should be' how many electrons can the hydrogen and chlorine used for bonding.

Chlorine is in Group 7 so it has 7 electrons.
If it combines with a metal group, then it can only accept 1 electron from the metal. ( so that add up to be 8 electrons )

If it combines with a non-metal group, then it can share only 1 electron from the non-metal thus forming 8 electrons too.

In this case, if chlorine combines with hydrogen to form hydrogen chloride, then only 1 bond is formed between hydrogen and chlorine.

ms pang :)

Groupings for March Holiday's Project

Dear all,

please double check your grouping,

Group 1: Ionic compound (NaCl, MgCl2)

Gareth
Mikhail
Chong cheng
Hong jie
Naufal

Group 2: Ionic Compound (NaF, CaCl2)

Jeremy
Yan seng
Nadi
Jovin

Group 3: Simple covalent molecules (H2O, CO2,CH4, O2,H2,Cl2, HCl, NH3, CO, C2H4)

June
Qian hui
Eileen
Bao yuan
Jun ling

Group 4: Simple covalent molecules (H2O,CO2,CH4,O2,H2,Cl2, HCl, SO2, CH3COOH)

Shi min
Candi
Fiona
Qi ying
Hao eng

Group 5: Macromolecules (diamond, graphite)

Jerry
Hung yih
Zi jun
Jian Qiang
Kevin

Group 6: Macromolecules (silicon dioxide, graphite)

nil

attention to shana, nicole, zhi ying, shermaine, celin and sheng lin you girls have not sign up for your topic!!!

Reply To Mark's Question: Is there such a substance CaClOH?

Mark asked: 'just to check, is there such thing as CaClOH ?'

My reply: Yes!!!! But not in your syllabus.

In the reaction of HCl and limestone under furnace and boiler conditions, CaClOH is an INTERMEDIATE product.

'intermediate product' means, the reaction produce this product and this product (known as intermediate product) will further react or continue in the reaction to form the final product.

If not, under NORMAL conditions, HCl will react with CaCO3 ( limestone) to form carbon dioxide, calcium chloride and water.

ms pang:)

Saturday Revision Topics: Group Properties

Dear all,

Some of you are not required to attend the saturday's remedial due to your better chemistry results. You may get a copy of the extra exercises ( 1st remedial- mole concept; 2nd remedial: Group Properties) from me every week on monday!

However, answers are not provided. Please complete on your own before seeking Mrs Jaya or myself for help.

As for the pupils who have been attending the remedials regularly, please continue to do so.
It is easier to revise and complete the exercises with help rather than struggling to complete it on your own! In addition, you can clarify your doubts!

Apologies for the cancellation of 2 slots due to my revision for 3A3 today.

The attendance is as follows:

Michael, Yazid, Cheryl and Natasha ( 10-11am)
Cheng Hong, Yanne, Acslyn [ i spelt correctly:) ], Geok Teng ( 11-12pm)

Amendment To 4E1/4E4 Science Chemistry Common Test Topics

Dear 4E1/4E4,

There are a total of 5 topics for your common test on 20th feb.

The topics are:

(1) Chemical Bonding

(2) Mole concept

(3) Periodic Table and Group Properties

(4) Metals

(5) Redox ( reduction and oxidation )

Sorry for the amendment :(

Time slots for next saturday remedial 16 Feb 2008

Dear 4E1/4E4 pupils,

Attendance is COMPLUSORY for pupils who failed the metal test or the mole concept test!!

i will be revising metals (especially displacement reactions) and simple redox ( reduction and oxidation ) on 16 Feb.

These are the time slots:

(1) 8.30 am-9.30 am
(2) 9.45 am-10.45 am
(3) 11.oo am- 12.00 pm

Note:

(A) Maximum pupils per group will be 4.
(B) Please bring along textbook and Five Year Series.
(C) If all the slots are filled, you have to see me anyday from Monday-Thursday.

For administration purposes:
These are the pupils who attend the mole concept revision on 09/02/08.

-acsyln, ronald, jolene
-keith, cheryl , natasha
-cheng hong, geok teng

Latest News For Sec 5 Normal Academic Science Chemistry Common Test on Week 7 / 8

The topics tested for Science Chemistry Common Test (5A) on week 7/8 are as follows:

(1) Bonding ( ionic, covalent and their properties )

(2) Mole concept

(3) Metals ( properities of metals, extraction of metals, uses of metals and recycling )

(4) simple oxidation and reduction

(5) Periodic Table

Please pass this information around:)

Latest News For Normal Academic Science Chemistry Common Test on Week 7 / 8

The topics tested for Science Chemistry Common Test (4A1-4A3) on week 7/8 are as follows:


(1) ionic and covalent bonding



(2) mole concept: calculating reacting equations



(3) acids, bases and salts ( including oxides- acidic, basic and amphoteric )

Please pass this information around:)

Latest news for chemistry common test on week 7/8

The topics tested for Science Chemistry Common Test (4E1/4E4) on week 7/8 are as follows:

(1) ionic and covalent bonding

(2) group properties [ group 1,7,8 ]

(3) metals [ properties of metals, reactivity series of metals, extractions (esp. iron ), recycling ]

(4) oxidation and reduction

Note: Five year series will be available to you guys on thursday 31st jan 08, so you guys will be able to practice the questions. Will keep you inform what questions to practice.

Pass this info to your friends/classmates:)

Some Tips for Qualitative Analysis

A lot of pupils fare badly for Qualitative Analysis.

Students are unable to choose the appropriate test for identifying the gas evolved.

Typical Scenario:
When a gas evolved from a reaction, pupils used All the various test to identify the unknown gas.
Before the correct test can be used to test for the unknown gas, the reaction stopped to produce any gas!!!!

So how?!?

You can deduce the identity of a gas ( before actually testing ) by:

*** 1.The reactions that produced the gas.

2.The odour of the gas.

3.The colour of the gas, (whereby in your syllabus), chlorine is yellowish green.

For hydrogen gas

the reagents used will surely be acids and metal strips...

if you did not used any shiny powder ( probably metals ) or shiny strips, then the test for hydrogen is NOT NECESSARY because hydrogen gas will never be produce when the reagents are not acids and metals!!! so, please do not test with burning/lighted splints.

For carbon dioxide gas

carbon dioxide only evolved when you heat a carbonate or you react an acid with a carbonate. So, if you are not using a dull powder (or dull solids) then no need to test for carbon dioxide gas!!

For oxygen gas

oxygen gas will not be produced from acid-base/acids-metal/acids-carbonate reactions!!!!

oxygen gas reactions can be very tricky....

because there are a few reactions that produce oxygen gas.

Eg- adding manganese oxide to hydrogen peroxide and heating nitrates.

Pupils always expect the glowing splint to rekindle BRIGHTLY... however, in most reactions, this does not happen.

The reason is simple.... the amount of oxygen gas produced from your 1-heap spatula and 2cm3 of solvent is not enough to produce alot of oxygen gas!!!! Should you observe a slight glow/brightens, you can safely deduce the unknown gas as oxygen.

Lastly pupils need to know HOW TO CONCENTRATE GASES

Pupils need to use their thumb to cover the openng of the test-tube to 'concentrate' the gas.

This is to ensure the gases will be enough to create a clearer result. Most of the time, pupils failed to observe the result because the gas that travels from the reacting mixture to the opening of the test-tube is too little.

hope that you find this useful!

Studying Strategies :)

Ever wonder why you STILL score a C5-6 grade even though you do school work/ studied at home/pay attention during lessons?

seems no justice ?!?

Well, justice can prevail ... read more to find out......

(1) Know what is the most/more important ideas of the topic

It is no use memorising the whole topic......
there are times pupils memorised chapters/practise a particular concept and spend 1 week for revision of a topic where it will only be of a weightage of less than 3 marks in exam!!!

the next question you would ask ," but we don't know what is important for the exams? "

then, you have to (1) ask the teachers; (2) see which questions are usually/ frequently tested in the past year papers!!!

(2) Know the mark allocation of the question

Most pupils waste their time by writing more than 4 sentences for a 1 mark question!!!

Pupils need to know that [1 mark] is approxiamtely 1.5 minutes.

Hence, every sentence you write will be equivalent to almost [ 1/2 mark ]. In other words, pupils should not have any 'waste move'. again, if pupils do not know the mark allocation for the question, please seek teachers advise!!!!

(3) Know how to identify the question to the chapter and to link common answers to the question

This is an extremely important strategy!!!!!

Usually, pupils failed to identify the question to the relevant chapter. As such, they have difficulty in suggesting reasonable answers.

Example,

sodium chloride and chlorine gas are substances of chloride. Explain why sodium chloride has high melting point while chlorine gas has a low melting point.

Suggested answers from pupils :

sodium is a metal and chlorine is a non-metal, hence sodium chloride is high melting point; chlorine gas is a non-metal, hence low melting point.

Does this solution make sense?!?

Firstly, this solution does not need any information from the topic-bonding. Any secondary 1/2 will be able to identify whether sodium is a metal or not from the periodic table!!!!

Strategy: When a pupil sees this question. The pupil MUST identify the topic which is bonding.
From bonding, try to recall the words-' ionic bonding' and 'covalent bonding'.... ( no other chapters talks about bonding, so it is very obvious )
from ionic bonding-- try to link it to electrostatic forces of attraction while covalent bonding, link it to weak intermolecular forces of attraction.

Generally, teachers will inform pupils to memorise the reason for high melting point. The sentence goes like this, " sodium chloride is an ionic compound, a large amount of energy is needed to overcome the strong forces of attraction between oppositely charged ions, hence high melting point. On the other hand, chlorine gas is a covalent molecule. A small amount of energy is needed to overcome the weak intermolecular forces of attraction between the molecules. Hence low melting point. "

If you can remember the topic correctly, should be able to ring a bell and will be able to write a few sentences from the 'standard answers by teachers'......

that's all for my sharing :)

May the force be with you

Replying Ronald's Question: How do we know the valencies of ions?

Ronald asked:

Ms Pang, hw u noe whether the Element electron charge is -2, -1, +1 or +2

My reply:

an ion ( not element ) will have a charge of minus or plus depends whether it is a metal or non-metal.
For metal, it tends to form ions of charge +1, +2, +3 ( cations- lose electrons )
For non-metal, it tends to form ions of charge -1,-2 ( anions - gain electrons )

ms pang:)