Homework 4 (due 27th April)

Dear CH304,

Predict with suitable explanation which compound has stronger inter-atomic bond, BeBr₂ or AlBr₃?

Answer
BeBr₂ and AlBr₃ covalent compounds. If both were ionic compound, both compound contains a very small and highly charge cation and a large anion. This results in the cation to polarise the anion's electron cloud, hence making electron clouds to overlap.

Since both BeBr₂ and AlBr₃ are covalent compounds, Be is a smaller atom than Al. Hence, the extent of overlapping of atomic orbital between Be and Br is greater than in Al and Br. Hence, Be-Br single bond is stronger than in Al-Br single bond.

Comments
The most comprehensive answer goes to Xing Ting, Johanan, Wei Jie and Dung. =)

The following are the misconceptions made. I have included the names so that we can all learn from each other. I think it wld be excellent if you would like to take this question into further discussion.

1. Stating that BeBr₂ and AlBr₃ are dative covalent compounds. Please don't say that. Covalent compound is good enough. - Eileen's answer

2. Not applying to the definition of covalent bond (key words missing out) completely. - Eileen's, Jo's, Daniel's

3. Thinking that BeBr₂ are AlBr₃ ionic compounds - Xiao Min's, Lyria

4. Incomplete sentence expression (with ambiguous word(s)). - Sherlyn (what is it?), Jing Yew (Am i going to assume that you meant covalent bonds are formed?)

5. Totally missing the point. Thinking that I am trying to account for dative bond or why covalent bond, when I am actually trying to determine strength of bond. - Peck Fen, Wen Han, Brandon

6. Writing irrelevant information (e.g. "Bond pair replusion", "more bonds bonds formed around Al, does not mean the bond is stronger", "VSEPR" and "Charges of Be and Al") - Renaldy, Benjamin, Crystal, Kevin, Nicholas

7. Trying to answer too much. Uses both definition of covalent bonding. (can get abit confusing). - Samuel

Chemical Energetics - Calorimetry

Almost all chemical reactions produce heat. In the production of heat, experiments are conducted to investigate the amount of heat the reaction produced per mole of substance reacted. However, there are experiments which are conducted to investigate the amount of heat the reaction produce per mole of product formed.

Enthalpy change of reaction is defined as the amount of heat produced by the reaction per mole of substance reacted. Specific chemical reactions have their own enthalpy change definition such as Enthalpy change of neutralisation and enthalpy change of combustion. These definitions will be highlighted in another entry.

Hence, this post aims to explain how an experiment is done so that we can investigate the amount of heat the reaction produced per mole of substance reacted. These experiments are know as calorimetry. There are three different situations that can occur in a common laboratory.

(1) Using a water-beaker calorimeter.

In this experiment, a water-beaker calorimeter is set up as shown below. The combustion reaction occurs below the calorimeter and heat is transferred from the reaction to the calorimeter. The temperature of the solution in the calorimeter increase and using the formula shown below, we can obtain the enthalpy change of combustion. Do note that c = specific heat capacity of water, m = mass of water in the beaker and the negative sign implies the reaction is exothermic (releases heat).

Another formula is in the above picture. This formula uses C, which heat capacity of the calorimeter. The capital C is independent of the mass of the calorimeter. Hence, in this situation, it is the temperature change of the calorimeter which we measured.

(2) Mixing two solutions together.

The diagram below illustrates the steps taken. Usually, this method is done when the two reactants are in aqueous solutions. When these reactants are mixed together, the chemical reaction will transfer or absorb heat from the solution. When the reaction absorbs heat, such reaction is endothermic and the enthalpy change has a positive sign.

(3) Adding solid into an aqueous reactant.

The illustration below illustrates the steps taken. This method is used when one of the reactant is a solid and the other is an aqueous solution. From the formula below, note that V = volume of the solution, while c = specific heat capacity of the solution.

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Article written by Kwok YL 2009.}

^{Disclaimer and remarks:}

• ^{If you would like to use this source, kindly drop me a note by leaving behind a comment with your name and institution. I am all for sharing as the materials on this blog is actually meant for the education purpose of my students.}
• ^{This material is entirely written by the author and my sincere thanks will be given to anyone who is kind, generous and gracious to point out any errors.}

Homework 3 (due before 20th April 2009)

Dear CH304,

Question

You have learnt about the oxidising agent KMnO₄. This reagent is made up of potassium and permanganate ions. In an ion of MnO₄^-, there is covalent bond between Mn and O. By using your knowledge from these posts, (i) suggest plausible reason(s) to why covalent bond exists between Mn and O and (ii) to why a dimer or polyer is not formed (which is what happen in AlCl₃ and BeCl₂ respectively.).

Suggested Answers

(i) If ionic bonding occurs in MnO₄^-, the Mn must exist as a Mn⁷⁺. This cation will be very small and will have a very large change, hence highly polarising. O^2- is generally quite small, but when placed next to a Mn⁷⁺, it will polarise the electron cloud of O and hence resulting in an overlapping of electron cloud between Mn and O. Therefore, covalent bond exists between Mn and O instead.

(ii) Usually such structures, we will expect to see that the metal atom will contain empty orbitals while the non-metal atom will contain available lone pair of electrons of donation. This results in a formation of dimer (Al₂Cl₆) or a polymer (e.g. BeCl₂). In the situation of MnO₄^-, it is possible to suggest that O being a highly electronegative element is reluctant to donate its lone pair of electrons to form dative bond. Hence, there is no dimer formed nor polymer.

Common errors and comments

There some nice answers given by your classmates. I reckon that Jing Yew provides the best answer. Joey gave me a very detailed analysis to why the bonding between Mn and O is covalent for MnO₄^-. Wei Jie also provided me with a good answer to why the bond between Mn and O is covalent.

Basically, I required you to make use of the ideas to suggest why a metal and non-metal produces a covalent bond between them. In addition, to account for formation of dative bond. If you notice, generally covalent compounds are metal and non-metal combination, it is capable of dative bond. - This is not the case for MnO₄^-

1. Suggesting that a Mn²⁺ will exist in MnO₄^-. This is not true.

2. Mn has no empty orbital - Actually I do not think I can conclude that. I think the d orbital is available. And since Mn has the electronic configuration of 1s²2s²2p⁶3s²3p⁶3d⁵4s², it should still have empty orbital available for lone pairs of electrons donated to it.

3. Some fail to conceptualise why AlCl₃ exists as a dimer. That idea is discussed in tutorial and explained over here! There is a weakness in conceptualising the phenomenon of AlCl₃.

4. I don't understand what has octet got to do with the type of bond formed between Mn and O.

5. The only two ways to account for why MnO₄^- has covalent bonds between Mn and O: (i) The above answer. (ii) Using IE. It takes up too much energy to form Mn⁷⁺, hence the ion prefers to have covalent bond instead.

6. One of you mentioned about orbital overlap, since Mn 3d and 4s are relatively close in energy. I would think that by saying these orbitals overlap presupposes that covalent bond is formed. I am actually curious then to why this doesn't occur to the other metals.

7. Some mentioned that O lacks lone pair. That is not true.

8. Mass of the atoms is irrelevant to the charge density.

Announcement

Dear CH304 aka SCones,

After looking through your weekend assignment, I am pleased to thank you for allowing me to clarify a content information found on this blog.

I have previously mentioned that the s orbital is smaller than the p orbital. After reading your homework and searching a few textbooks, I realised that it is inaccurate to say so (in fact only wikipedia thinks that the s orbital is smaller). Hence, I would like to thank you for this clarification.

Please read through the edited atomic structure article. In addition, you will be pleased to read more about chemical bonding over here.

Regards
A delighted Mr Kwok

Chemical Bonding - Intermolecular Forces

Substances that contains covalent bond between their constituent atoms have two possible structures: Either (1) Simple discrete molecules or (2) Macromolecular structure (as known as Giant Molecular Structure). Substances that exist as simple discrete molecules have covalent bond between the atoms, while they have intermolecular forces between the molecules. This is a fact which you must be able to distinguish.

A simple guide I have often used to determine whether a substance exists as either (1) simple discrete molecule or (2) macromolecular, would be to see if I am able to draw the dot and cross diagram of the substance. If I can draw a finite dot and cross diagram showing sharing of electrons, that substance will exist as a simple discrete molecule. The following illustration show examples of finite dot and cross diagrams and their corresponding Lewis structure.

When we can establish that a substance exist as a simple discrete molecule, we will need to determine the shape of its molecule. The shape of the molecule play a role in determining the intermolecular forces that exist between the molecules. The pictures below provide a guide to how to determine the shape of the molecule.

There are two broad types of intermolecular forces, van der Waals Forces and Hydrogen-bonding. The former can be divided to (1) Induced dipole - induced dipole (id-id) interactions and (2) Permanent dipole - permanent dipole (pd-pd) interactions.

All molecules contain id-id interaction as this form of interaction is due to a temporal unequal distribution of the molecule's electron cloud, which result in a side of the molecule to have smaller electron density, while the other side has more.

Non-polar molecules have only id-id interaction between their respective molecules.

While polar molecule can have either pd-pd interactions or Hydrogen-bonding as the pre-dominant (note the I used pre-dominant instead of "only") intermolecular forces.

Hydrogen-bonding is a unique case of pd-pd (thus, Hydrogen-bonding is an intermolecular force of attraction). Polar molecules which has a highly electronegative atom such as N, F, and/or O and this electronegative atom is attached to O will show Hydrogen-bonding.

With the knowledge of shapes of molecules and intermolecular forces, we will soon be able to effectively discuss how to account certain physical properties of the substances.

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Article written by Kwok YL 2009.}

^{Disclaimer and remarks:}

• ^{If you would like to use this source, kindly drop me a note by leaving behind a comment with your name and institution. I am all for sharing as the materials on this blog is actually meant for the education purpose of my students.}
• ^{This material is entirely written by the author and my sincere thanks will be given to anyone who is kind, generous and gracious to point out any errors.}

Chemical Bonding - Strength of Interatomic Bonds (Part 2)

This article is an continuation of the article on interatomic bond. In this writeup, I shall discuss about the factors that affect the strength of the ionic bond and metallic bond. In trying to account for the strength of these bonds, it useful to make use of this rule: Always refer to the definition to how these bonds are formed first. (E.g. refer to the definition of covalent bond and then apply it in trying to account for the varying strength of different covalent bonds.)

(B) Strength of Ionic Bond.
Definition: Ionic bonds are formed because of electrostatic attraction between oppositely charge ions.

The following diagram illustrates how the ionic bond is affected. Strength of ionic bond is affected by lattice energy, which is directly affected by the product of the charges of the ions and inversely affected by the sum of the ionic radii.

(C) Strength of Metallic Bond. (using the sea of electrons model)
Definition: Metallic Bonds are formed because of electrostatic attraction between the cation of the metal and the sea of electrons.

Using the definition of metallic bonds, a metal atom which has more valence electrons will be able to contribute more electrons to the sea of the electrons. Hence, this result in a cation which has a greater positive charge. Therefore, the electrostatic attraction will be greater.

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Article written by Kwok YL 2009 (updated May 2009).}

^{Disclaimer and remarks:}

• ^{If you would like to use this source, kindly drop me a note by leaving behind a comment with your name and institution. I am all for sharing as the materials on this blog is actually meant for the education purpose of my students.}
• ^{This material is entirely written by the author and my sincere thanks will be given to anyone who is kind, generous and gracious to point out any errors.}

Chemical Bonding - Strength of interatomic bond (Part 1)

This article is an continuation of the article on interatomic bond. In this writeup, I shall discuss about the factors that affect the strength of the covalent bond. In trying to account for the strength of these bonds, it useful to make use of this rule: Always refer to the definition to how these bonds are formed first. (E.g. refer to the definition of covalent bond and then apply it in trying to account for the varying strength of different covalent bonds.)

(A) Strength of Covalent Bond:
Definition 1: Covalent bond is formed when there is electrostatic attraction between shared electrons and the nuclei of the two atoms.

When an atom is large, this will result that its valence electrons to be found further for the nucleus. In addition, the atom only make use of its valence electrons to form the covalent bond. Hence, when two larger atoms form a covalent bond with each other, their shared electrons will be significantly further away for the nucleus. Hence, the electrostatic attraction is weaker.

Definition 2: Covalent bond is formed when there is an overlapping between two atomic orbitals.

The atoms make use of their atomic orbital, where the valence electrons occupies, to overlap with each other and hence the a covalent bond is formed. The larger the atom, the less effective the overlap. Hence, the weaker the covalent bond.

Explanation - Strength of Covalent Bonds.
In addition, because of the definition of potential energy, this result in the covalent bond of H-H to be stronger and yet lower in potential energy than the Cl-Cl bond. This is succintly illustrated by the diagram below. Hence, lower potential energy implies greater electrostatic attraction between shared electrons and nuclei.

Lastly, bond energy refers to the amount of energy required to break a covalent bond. A larger bond energy implies that more energy is required to break a covalent. Hence, small atoms form strong covalent bond because the distance between shared electrons and nuclei is small. Therefore, greater electrostatic attraction, which results in more energy required to overcome this attraction, thus small atoms form bonds with large bond energies.

Other factors that affect strength of covalent bonds include: A polar covalent bond strengths the bond between two atoms. In addition, when two small atoms each having a lone pair of electrons, there is repulsion between the electron pairs hence, weakens the covalent bond.

In summary, using the other concepts you see in covalent bonding, the following flow-chart will be useful when we try to explain the different strengths of covalent bonds.


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Article written by Kwok YL 2009 (updated May 2009).}

^{Disclaimer and remarks:}

• ^{If you would like to use this source, kindly drop me a note by leaving behind a comment with your name and institution. I am all for sharing as the materials on this blog is actually meant for the education purpose of my students.}
• ^{This material is entirely written by the author and my sincere thanks will be given to anyone who is kind, generous and gracious to point out any errors.}

Chemical Bonding - Covalent bonds with a twist

Generally, the bond formed between a metal atom and a non-metal atom is that of an ionic bond. The metal atom will transfer its valence electron(s) to the non-metal atom such that both will become cation and anion respectively. In this manner, both will attain the favourable octet.

While, the bond between two non-metal atoms is that of a covalent bond. Neither atoms is willing transfer electrons to each other, hence to obtain the favourable octet both atoms would share a certain number of valence electrons. This sharing can take place when the atomic orbital of both atoms overlap.

(A) Seemingly ionic compound but are actually covalent.

AlCl₃ has covalent bonds between Al and Cl. This is contrary to what is expected.

If AlCl₃ was a ionic compound, the Al³⁺ cation is small and has a large charge, hence this cation is willing to polarise the electron cloud of the anion.

Cl^- is a large anion whose electron clouds are easily polarised. Polarisablity refers to the ease of distorting the electron cloud. When place next to Al³⁺, the electron cloud of Cl^- is distorted by Al³⁺. This severe distortion allows for both electron clouds to overlap. When that happens it mimics the overlapping of orbital hence covalent bond is formed.
Interesting, in a single molecule of AlCl₃, its dot and cross diagram does not fulfill the octet rule. This is because Al has only 3 valence electrons and even when all three are shared, there is only 6 electrons around Al. Hence, I must stress that this is not the norm. Usually, this rule is satisfied.

(B) Covalent bonds that carries some charge.

The assumption of a covalent bond is that the shared electrons are equally shared. This idea also suggests that the distance between the nucleus of one atom and the shared electrons is the same. However, this is not the case. Different elements' nucleus has different attractive power; some are more abled to pull electrons towards itself and hencce the term "electronegativity is introduced."

When the atom is more electronegative, it pulls the electrons closer to it. Hence when two atoms of differing electronegativity are bonded together, the atom which is more electronegative will pull the shared electrons closer to it.

This results in the less electronegative atom to carry a slight positive charge, while the other atom carries a slight negative charge. Since there is a small slight charges being produced,the two atoms are further held together because of electrostatic attraction between the partial charges.
In conclusion, we still need to bear in mind that the electrons are still shared between the two atoms; it is just now the shared electron is found closer to one nucleus than to the other. Therefore, a polar covalent bond is produced.

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Article written by Kwok YL 2009.}

^{Disclaimer and remarks:}

• ^{If you would like to use this source, kindly drop me a note by leaving behind a comment with your name and institution. I am all for sharing as the materials on this blog is actually meant for the education purpose of my students.}
• ^{This material is entirely written by the author and my sincere thanks will be given to anyone who is kind, generous and gracious to point out any errors.}

Chemical Bonding - Dative Covalent and Expansion of Octet

In these posts I shared about how interatomic bonds are formed and the factors affecting their strengths. While in this entry, I will be elaborating more about covalent bonds.

The earlier models of covalent bonds taught us that covalent bonds are formed when (1) the shared electrons used to formed the covalent bond must each come from the two constituent atoms and (2) the non-metals seek to attain an octet, hence search to have 4 electron pairs aroud it, therefore resulting in a maximum of 4 single bonds. These knowledge is still applicable, however, there are extensions.

(A) Dative covalent bonds.

Dative covalent bond are formed when an electron pair used to form a covalent bond between two particles come from just one source. Hence, this implies that one of the particles needs to have a pair of non-bonding electrons for donation and the other particle contains an empty orbital to accept the electron pair. I have illustrated using an example of an adduct formed by AlCl₃ and NH₃.

My second illustration of dative bond formed is using just AlCl₃. This compound usually exists as dimer and it is because Cl has available lone pair while Al has an empty orbital to accept the electrons. Interestingly, the Cl does not donate its lone pair of electrons to the Al it is attached to in a molecule; it rather donates its lone pair to a Al which is found on another molecule. This is because to form a double bond between Al and Cl is unfavourable as compared to having to form a dative covalent bond.

You may learn more about why AlCl₃ is a covalent compound over here.

(B) Expansion of octet - Having more than 8 electrons.

Elements found in Period 3 and below show an unique property. These elements show that the expansion of the octet is possible. For example, sulfur can exist as SO₂. In this molecule, S satisfies octet rule. While sulfur can also exist as SO₃ and in this molecule, S has more than 8 electron around it. This shows that S has expanded its octet (This is illustrated below.) It is because S contains empty low-lying 3d-orbtials which are available to accept more electrons.

Lastly, one needs to be mindful, when the octet is expanded, we will still get even number of electrons - all the electrons are paired. Hence, we will not observe 9 electrons or 11 electrons.
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Article written by Kwok YL 2009.}

^{Disclaimer and remarks:}

• ^{If you would like to use this source, kindly drop me a note by leaving behind a comment with your name and institution. I am all for sharing as the materials on this blog is actually meant for the education purpose of my students.}
• ^{This material is entirely written by the author and my sincere thanks will be given to anyone who is kind, generous and gracious to point out any errors.}

Homework 2 (due before 13th April 2009)

Dear CH304,

This weekend's assignment. Last week's assignment can be found here.

In the current course of Chemistry, you have learnt that MgCl₂ exists as a giant ionic lattice structure. While, H₂O is a simple discrete molecule. This implies that ionic bond exist in MgCl₂, while covalent bond exists in H₂O. Suggest an explanation to why MgCl₂ is not covalent. In addition, suggest why H₂O is not ionic. You are highly encouraged to use the following articles as a stepping stone.

1) Atomic structure - Introduction
2) Chemical bonding - Interatomic Bonds

Suggested Answer

Mg has two valence electrons while Cl has 7 valence electrons. In order for Cl to obtain the octet configuration it needs 1 more electron. There are two possible ways this may be done: (1) gaining an electron from a donor. (2) Through sharing of electrons, Cl gains the 8th electron. The third way will be for Cl to lose all its 7 valence electron and this is not possible because it would require too much energy.

If Cl obtain its 8th electron through sharing of electrons with Mg, thus resulting in a Mg-Cl covalent bond to be formed between Mg and Cl. This results in Mg to have only 4 electrons; 2 of its own and 2 derived through sharing. This is a far short of octet.

Hence, Mg will prefer to lose 2 electrons. The energy required to remove 2 electrons is compensated by the ionic bond formed between Mg²⁺ and Cl^-. Therefore, MgCl₂ exist as an ionic compound.

While in the situation of H₂O, the sharing of electrons will allow both H and O to obtain the full shell configuration. Hence, water has the covalent bond, O-H, and it exists as a simple discrete molecule.

If H₂O exists as an ionic compound, it is not possible for O to ionise all its valence electrons as that is energetically not feasible. In addition, for H to ionise its electron to give H⁺ will not be favourable too. This is because H has only 1 quantum shell. The close proximity between the valence electron of H and the nucleus requires a huge amount of energy to ionise the atom H. Therefore, these scenarios explain why ionic bonding cannot occur between H and O in H₂O.

Comments
There are some decent attempts in trying to answer, but there are some of the glaring misconceptions or inabilities to account:

(1) Unable to do a proper compare and contrast to why some compounds exhibit ionic bonding while other exhibit covalent.

(2) Those who tried to do the compare and contrast gave very superficial comparisons, like using electronegativity difference, or electronegativity etc, these highlight that one did not really understood how these two interatomic bonds were derived. Electronegativity difference shows us a pattern to why certain bonds between particles are ionic and others are covalent; BUT they are not the reason to why those interatomic bonds are formed.

(3) Did not highlight why it is improbable for covalent bond for MgCl₂ and ionic bond for H₂O.

(4) Using polarising power to determine bonding is a poor use of principle. This principle is used to explain anomalies. It is not use to explain for the bonding in the first principle.

(5) This activity does highlight that critical analysis of data and principles is something that you would like to work on. The combination of Johanan (for MgCl₂ and Sherlyn's (for H₂O) answers give a indication of what I consider as critical analysis.

In conclusion, I think these set of assignments will start to allow us to think carefully about a statement and think more carefully about the fundamentals and hence facilitate the learning of this topic.

Atomic Structure - Energy Level

In the study of atomic structure, there is a certain set of ground rules (please refer to lecture material for basics) which we make use to fill electrons. These rules are formulated because we fill electrons in shells, subshells and orbital which are of lower energy level first.

The following diagram illustrates the three main orbital which we are required to know at the GCE "A" Level curriculum. Of these three orbitals, the s-orbital has the lowest energy while the d-orbital has the highest.

This electrostatic attraction will result in the s-orbital to be of lower energy. This is abit perplexing, but we need to rationalise that electrostatic attraction is a form of potential energy (PE).

By definition, potential energy is a negative number and the weakest potential energy is at infinity. In that case, PE = 0. Hence, a greater electrostatic attraction will result in a larger numerical value of PE, but because of the definition of PE, the energy is lowered.
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Article written by Kwok YL 2009.}

^{Disclaimer and remarks:}

• ^{If you would like to use this source, kindly drop me a note by leaving behind a comment with your name and institution. I am all for sharing as the materials on this blog is actually meant for the education purpose of my students.}
• ^{This material is entirely written by the author and my sincere thanks will be given to anyone who is kind, generous and gracious to point out any errors.}

Homework 1 (due before 6th April 2009)

Dear 1CH304,

Critically comment the following quote:

"A An atom is a very small particle. It is able to be divided into smaller particles, known as protons, neutrons and electrons. These particles are sub-atomic particles and are the smallest particles of an atom. In addition, the atoms of an element are always identical. While the valence electrons of an atom are always degenerate. The chemical property of an atom is largely determined by the protons of the atom."

There are 5 errors in the above quote. Quote the relevant sentences and explain the error(s).

You may wish to this and/or that as resource materials to answer this question.

Suggested Answer
.... are the smallest particles of an atom

(1) This is not true as we have learned that protons, electrons and neutrons can be subdivided. However, we don't need to know the details.

the atoms of an element are always identical

(2) The existence of isotopes refute this statement. For example, the element hydrogen has 3 isotopes, ¹H, ²H and ³H.

..valence electrons of an atom are always degenerate

(3) Degenerate means that the valence electrons are found on the same energy level. That is not true. Using oxygen as an example, it has 6 valence electrons. It's electronic configuration is 1s²2s²2p⁴. The 6 valence electrons are found on 2s and 2p. Clearly, 2s and 2p are of DIFFERENT energy levels.

..chemical property of an atom is largely determined by the protons of the atom

The above statement has two errors:
(4) It is the valence electrons of an atom that determines its chemical property.

(5) The protons and neutrons (hence the nucleus) affects the physical property.

Comments

Generally there are many good answers! I am pleased and I am confident we can expect better ones in the future. However, the accuracy of the explanation was quite weak.

(1) Atoms are very small particles. The atomic radius is close to 10^-9 m, it is indeed very small!

(2) There are a few who struggled in their explanation of degenerate. The orbital in a subshell are degenerate, however two subshells are not degenerate. Interestingly, there are a few who did not know the meaning of degenerate.

(3) Some have left out the explanation and hence their answers were marked down as it did not adhere to the requirement of the question.

Carbonyls - Nucleophilic Addition Mechanism

In the study of the reactions involving carbonyls, one of the most important reactions is the nucleophilic addition reaction (You may like to refer to the definitions of reactions by clicking here.). This is similar to the reactions involving alkylhalides as both requires nucleophiles and electron-deficient carbon atoms. However, carbonyl will show an addition across a double (this time is the C=O), while the alkyl halides shows a replacement (aka substitution.)

The most significant nucleophilic addition reaction which we study in detail, is that between a carbonyl molecule and hydrogen cynanide. This reaction is studied in sufficient detail such that we are able to identify the most suitable conditions for the reaction. In addition, we were able to understand how sometimes NaOH or NaCN were used in trace amounts to boost this reaction.

Racemic mixtures can be formed in the reaction between the carbonyl and HCN. This is because the carbonyl is planar and the nucleophile can attack either side of the plane (of carbonyl) in equal probability. In addition, the carbonyl must first be asymmetrical. If the carbonyl is symmetrical, no racemic mixture is formed.

The following diagrams depicts the illustration of mechanism of the nucleophilic addition reaction when NaOH or NaCN is being used.

(i)When NaCN was used - Regeneration of CN^-:

(ii)When NaOH was used - Regeneration of OH^-

While, the following video helps to demonstrate how the mechanism is drawn.

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Article written by Kwok YL 2009.}

^{Disclaimer and remarks:}

• ^{If you would like to use this source, kindly drop me a note by leaving behind a comment with your name and institution. I am all for sharing as the materials on this blog is actually meant for the education purpose of my students.}
• ^{This material is entirely written by the author and my sincere thanks will be given to anyone who is kind, generous and gracious to point out any errors.}