20 April 2010


Apa caranya? Tulis surat. Contoh soalan, anda dikehendaki membalas surat kawan anda yang ingin mengetahui tentang diri anda dan juga keluarga anda. Selain itu, kawan anda mengucapkan tahniah kepada anda kerana masih kekal berada di kelas pertama. Kawan anda ingin mengetahui serba sedikit rahsia kejayaan anda. Kawan anda juga bertanya kepada anda tentang subjek kimia tajuk jadual berkala berkenaan group 18 elements.Jadi, anda pun jawablah surat kawan anda tu..Try dulu..seronok tu tulis surat..Jangan biarkan kawan anda tertunggu-tunggu surat dari anda..Anda hanya perlu kreatif sedikit ja..Tengok contoh pelajar saya tahun 2009 buat surat untuk kawannya ya. Saya copy ja. taklah ikut format dalam ni. sekadar contoh...

Dzulyana Idhamsah,
Lot 296, Taman Merpati,
Lorong 4 Rendah,
Jalan Airport,
90000 Sandakan,

20 Mac 2009

Dear Aizat,
Assalamualaikum . How do you do ? I hope you and you’re family are in the pink of health in Lahad Datu, Sabah . My family and I are pretty good over here in Sandakan.

First of all, I want to apologize to you for late replying your letter over the last few days. I was so busy with my homeworks. Before that, thank you for your wish of congratulated me for still being the best student in my class. You also can become the best student in your class if you really want it.

I remember that you want me to explain about subtopic in chemistry which is alkenes. So now I’ll try to teach you a little bit about it that I know.

For your information alkenes are unsaturated hydrocarbon compounds. The functional group of alkenes is the double bond between two carbon atoms, C=C. Alkenes contain at least one double bond between two carbon atoms. The other carbon and hyrogen atoms are bonded together by single covalent bonds.

The molecular formula of alkenes can be written using the general formula of CnH2n, where n = 2, 3, 4... . The ‘n’ symbol represents the number of carbon atoms in the alkene molecule. The table below shows the molecular formulae of the first nine alkenes .

After learning that then you may learn to name the first nine alkenes. The ending name for all alkene members is ‘ene’. The naming of alkenes also based on the number of carbon atoms in the longest chain of the molecule. The next table below shows the names of the first nine members of the straight-chain alkenes.

Number of carbon atoms, n Molecular formula of alkene Initial name Ending name Name of the straight-chain alkenes
2 C2H4 Eth ‘ene’ Ethene
3 C2H6 Prop ‘ene’ Propene
4 C4H8 Buth ‘ene’ Buthene
5 C5H10 Pent ‘ene’ Pentene
6 C6H12 Hex ‘ene’ Hexene
7 C7H14 Hept ‘ene’ Heptene
8 C8H16 Oct ‘ene’ Octene
9 C9H18 Non ‘ene’ Nonene
10 C10H20 Dec ‘ene’ Decene

The next topic is the structural formula of the alkenes. The third table will shows you the structural formulae.

Now it’s time to explain about their physical properties. Those can be learning by understanding the table below.

Alkene Molecular formula of alkene Relative molecular mass Melting point (C) Boiling point (C) Physical conditon at room temperature Density at room condition (g/cm3) Solubility in water Electrical conductivity
Ethene C2H4 28 -169 -104 Gas 0.0011 Insoluble in water Does not conduct electricity
Propene C2H6 42 -185 -47 Gas 0.0018
Buthene C4H8 56 -185 -6 Gas 0.0023
Pentene C5H10 70 -138 30 Liquid 0.64
Hexene C6H12 84 -140 63 Liquid 0.68
Heptene C7H14 98 -119 94 Liquid 0.70
Octene C8H16 112 -102 121 Liquid 0.72
Nonene C9H18 126 -94 146 Liquid 0.73
Decene C10H20 140 87 171 Liquid 0.74

From the physical properties of alkenes shown in the table above, it can be concluded that:
(a) The melting point and boiling point of alkenes increase with the increase of the number carbon atoms per molecule.
(b) Three of the first alkenes (ethene to buthene) are in gas form at room temperature.
(c) The density of alkenes increases with the number of carbon atoms per molecule.
(d) All alkenes are insoluble in water.
(e) All alkenes do not conduct electricity.

Well, Aizat, I think my explanations about the alkenes are quite details and tough. I’ve got to end my letter here . I hope you can understand it and if you don’t then, you can ask me. It’ll be no problem for me to help you in this. Last but not least send my regard to your family. Bye.

Yours Truly,