Formation of Ionic Bond & Covalent Bond

Formation of chemical bond is one of the important concepts in chemistry. In Chemistry SPM, students are introduced ionic bond and covalent bond in when they were in form 4.

The following video shows the formation of ionic bond by using formation of sodium chloride as an example.
Ionic bond is the strong electrostatic force of attraction that holds the oppositely charged ions.

The following show samples of answer when explaining formation of ionic bond in essay Chemistry SPM.

• Electron arrangement of sodium atom is 2.8.1
• A sodium atom donates one electron to achieve stable octet electron arrangement
• A sodium ion, Na⁺ is formed
• This electron is transferred to a chlorine atom with an electron arrangement of 2.8.7
• A chlorine atom accepts electron from sodium atom to achieve the stable octet electron arrangement
• Chloride ion, Cl^-, is formed
• The sodium ion, and chloride ion, are attracted to one another by a strong electrostatic force/ionic bond to form an ionic compound, sodium chloride, NaCl.

The following video show formation of covalent bond. 
A bond that is formed when a pair of valence electrons are shared between two non-metal atoms.

There are three type of of covalent bond :

• single bond
• double bond
• triple bond

SPM Corner:
Electron arrangement for atom W : 2. 4
Electron arrangement for atom X : 2.8.7
Electron arrangemnt for atom Y : 2.8.8.2

Based on the given information, explain how two compounds can be formed from these elements based on their electron arrangements.

The two compounds should have different bond types. [10 marks]
[2005]

Guide:
Formation of Ionic Bond:

• State the electron arrangement of both atoms.
• Explain how each atom achieve stable electron arrangement. E.g. To achieve stable electrons arrangement, atom Y donates 2 electrons to form Y²⁺ ion while atom X donate 1 electron to form X⁺ ion 
• Explain the ions formed are attracted by strong electrostatic force.
• Give the formula of the compound formed.
• Draw the electron arrangement of the compound formed.

Formation of Covalent Bond:

• State the electron arrangemnt of and the number of valence electrons of each atoms.
• Explain how many more electrons for each atom to achieve stable electron arrangement. E.g. Atom W need 4 electrons to achieve stable electron arrangement while atom Y needs 1 electron to achieve stable electron arrangement 
• Explain how do the atoms share electrons. E.g. Atom W contributes 4 electrons for sharing while atom X contribute 1 electrons for sharing.  Each four Y atoms share 1 pair of electrons with one W atoms
• State the formula of the compound formed.
• Draw the electron arrangment of the compoud formed.

Definition of Isotopes

What's the definition of the isotopes? The video clip shows isotopes of hydrogen.


Sound simple, right? After watching the video clip, I hope you can identify some key words to define isotopes.

Isotopes are atoms that have the same number of protons but different number of neutrons. or

atoms that have the same proton number but different nucleon number.

My students used to give their definition of isotopes as follows:

1. same number of proton but different number of neutrons
2. same proton number but different neutron number.

Sadly, their answers are not considered as a complete definition., The first answer didn't mention the most important keyword: atoms. The second answer used "neutron number" which is incorrect term.

Some examples of isotopes :

1. carbon-12, carbon-13, carbon-14;
2. oxygen-16, oxygen-17, oxygen-18;
3. chlorine-35, chlorine-37.
4. chlorine-35 and chlorine-37.

Isotopes are widely in our daily life. Can you give some examples of isotopes used in medicine, industry, science and archeology?
In fact, the similar question turned out in SPM 2005.

Young Chemist - Sc & Tech Week Year 2010

Young Chemist was actually a competition! Students who have successfullly carried out the task given and showed an excellent work will be awarded as Young Chemist.

The task given was on a chemistry-related environment issues. Students were required to plan an experiment to study the the given problems. Students were given 2 hours in the chemistry lab to carry out their experiment plan and writing their report.

Based on students' report,  I found out that students understands the problems given. However, they were hardly to identify a specific problem they wish to study. They were able to plan required materials, apparatus, procedures and tabulation of data for their experiment. But analysis & interpreting data were their weakest part. This is the part that should be polished up. Form 5 students were weak in this part too in their PEKA.

The Young Chemist were awarded to groups from 4A, 4E and 4H. Congratulations!!!

 

Students were preparing chemicals for their experiment.

Students were pondering what to do next.

Students were interpreting data based on collected observation.

Students were working hard in writing their report.

Heat of Combustion of Various Alcohols

Heat of combustion of Various Alcohols from sweemoi khor

Characteristics of Homologous Series

In Chemistry SPM, students were introduced with five homologous series: Alkane, Alkene, Alcohol, Carboxylic Acids and Esters.

The following is one of the Chemistry SPM 2009 questions related to homologous series.
The table shows some information about three members of a homologous series.


Based on the table, state and explain five characteristics of a homologous series.                                        [10 marks]

1. Members of the series can be represented by a general formula. Ethanol, propanol and butanal have the same general formula, C_nH_2n+1OH
2. Successive members differ from each other by –CH₂. The difference between propanol and ethanol is CH₂ that has a relative molecular mass of 14.
3. Physical properties change regularly with increasing number of carbon atoms. The boiling points of alcohols increase from ethanol, propanol to butanol.
4. Members have similar chemical properties because they have same functional group. Ethanol, propanol and butanol undergo oxidatoin produce carboxylic acids.
5. Members of the homologous series can be prepared using the same method.  Ethanol, propanol & butanol can be prepared by hydration of alkene.

9th Malaysia Technology Expo

On 6 Feb 2010, I went with 52 students to 9th Malaysia Technology Expo held at PWTC.  It was wonderful study trip. Different universities has their own booths displaying their latest finding in science and technology.

There were few booths that attracted my attention:

1. Using Mas Cotek as Copper(II) Absorbent


















2. Polyethene/egg shell powder Composite
3. Polystyrene Composite as tiles

Atomic bomb on Hiroshima and Nagasaki

Today Hiroshima marked the 65^th anniversary of atomic bomb attack. Some chemistry related facts about the making of atomic bomb:

• The Hiroshima bomb which is called "Little Boy" used Uranium-235.
• The Nagasaki bom, "Fat Man" made of Plutonium-239.

More information related to the atomic bomb & World World II, click here.

Interpreting Energy Level Diagram

Interpreting energy level diagram from sweemoi khor

Exothermic Reaction vs Endothermic Reaction

Thermochemistry from sweemoi khor

Chemistry Pamphlet Design Competition - Sc & Tech Week 2010

Chemistry Pamphlet Design was one of the activity for Science & Technology Week Year 2010.  Each group of students picked a topic in their chemistry and submitted their work in 2 weeks time.

Students' submission for Chemistry Pamphlet Design Competition.

Winners of the Pamphlet Design Competition

Left: : The Periodic Table from 5G studentsMunirah, Hayati, Fadhilah)

Right : Esters from 5H students(Ashikin, Izzati, Zafirah)

It was my first time organizing such activity. To my surprice, most students with the help of ICT, they showed ability to find related information and present them well.

However there is always room for improvement for the following years. As for me, I would prefer giving a theme, e.g. Contribution of Chemists, Chemicals for Consumer, Manufactured Substances in Industry. Each group will conduct a detailed study on one of the topic, take photos and organize & present their information in a creative way.

As for the students:

• Avoid copying information 100% from any sources.
• Choose only relevant information.
• Using software like Microsoft Word/Publisher will help.
• Think of the audience. Must be eye-catching.  Use a suitable layout, font & graphics/photo and colour contrast.

Cleansing Agents – SPM 2008

Diagram shows the apparatus used to investigate how to remove an oily stain from a cloth and the observation made from that investigation.

(i) Compare and explain the effectiveness of the cleaning action between

• experiment I and III
• experiment II and IV.

(ii) identify the cleaning agents, A and B. State which cleaning   agent is more effective.

Suggested answer

(i)    Experiment I and III

• Both the cleaning agents A and B are effective in soft water. Soft water does not consist of calcium and magnesium ions.
• Both dissolves in soft water.
• They are able to lower the surface tension of water. The water wets the surface of the cloth thoroughly.

         Experiment II and IV

• Cleaning agent A is not effective in hard water. Hard water consists of calcium and magnesium ions.
• These ions react with the cleaning agent A to form an insoluble precipitate (scum). Formation of scum reduces the number of cleaning agent A molecules available for cleaning.
• Cleaning agent B is effective both in soft water and hard water.
• Cleaning agent B does not form precipitate (scum) in hard water.  Cleaning agent B form soluble salt in hard water. The cleaning agent B molecules are available for cleaning.

(ii) Cleaning agent A is soap; Cleaning agent B is detergent.

Detergent is more effective than soap.

Elelctrolytic Cell and Chemical Cells

In an electrolytic cell,

• Anion in the electrolyte move to  anode(connected to the positve terminal of the battery).
• Anions is selectively discharged by losing electrons(Depends at the concentration of ions in the electrolyte). In other words, anion is oxidized at anode. If metal electrodes are used instead of carbon electrodes, metal is oxidized to its metal ions by losing electrons.
• Cations in the electrolyte move to cathode(connected to the negative terminal of the battery).
• Cations which is at the lower postion in the Electrochemical Series is selectively discharged by gaining electrons. In other words, cations are reduced.

oxidation occurs at anode while
Reduction occurs at cathode.


In a chemical cell, 

•  Electrode which is more electropositive is oxidized to its ions by loses electrons, and acts as negative terminal.
• Electrons move through the external circuit and received by positive terminal.
• Cations in the electrolytes get attracted to the positive terminal and reduced to metal by gaining electrons.

Oxidation occurs at negative terminal.
Reduction occurs at positive terminal.

Control Iron Rusting by Using More Electropositive Metal

The hull of the Titanic has rusted since it sank in 1912.

Ship hull is protected by rusting by bolting magnesium bar onto it.  How does magnesium bar protect the ship from rusting? Explain.                                                                 [2 marks]

• Magnesium is more electropositive than iron. 
• Magnesium loses electrons more easily than iron.
• Mg --> Mg²⁺ + 2e^-
• Electrons move to iron. Therefore iron is protected by rusting

The same method is used controlling rusting of underground water pipes or steel utility pole. Blocks/stacks of magnesium is connected to the water pipes/steel utility pole by wires. Magnesium is  replaced from time to time when all magnesium corrodes.   This method is more known as sacrificial protection.

Peperiksaan Percubaan SBP SPM 2010

All the best! After the exam, the copy of the question paper and answer scheme will be available in this blog!

I love Chemistry