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Before continuing, here’s an ingelious way to solve mole concept questions with combustion.

Why is A Level Chemistry So Hard?

If you are taking A Level Chemistry, you will probably agree, like most students, that A Level H2 Chemistry is difficult and you have good reasons to do so.

The concepts are complex and involve much memory work.

There is a steep increase in the learning curve.

This is only natural.

Having now graduated from the top 20

Much Memory Work is Required

Chapters with many explanations to do include chemical bonding, all that organic chemistry reactions, the periodic table, and more.

What’s worse is that you often need to rely on your memory work to even answer the first question among a chain of others.

Data Booklet like this might help to a certain extent only.

If you don’t get the first question right, you often end up throwing the marks for the remaining questions away.

Such as:

Organic chemistry

Nothing can be worse than that.

Not knowing ALL the chemical reactions linking one functional group to another makes the whole study process much more frustrating.

Questions such as deductive types easily trip you if you miss out remembering the reagents or conditions for one or more reactions.

What’s more, reagents and conditions that can work for one reaction may not work for another.

Specialized reagents

Think of K₂CrO₇, or NaBH₄.

You can only use them to oxidize or reduce specific reactions.

Speaking of madness.

Polar molecules

And what about learning polar molecules must contain polar bonds and yet finding out later on not all molecules containing polar bonds have to be polar.

And the reason is that the dipole moments for all the covalent bonds will cancel and end up having zero net dipole moments.

This concept can be hard for students who have not studied vectors to appreciate.

I’m sure studying polar bears will be more interesting after this.

Here are 8 tips to deal with memory work.

Contradicting Explanations

Not only you are faced with tons of explanations to remember; more often than not, you will see them seemingly contradicting each other.

Nuclear charge and screening effect

Because moving across a period increases both the number of protons and electrons, nuclear charge and screening effect will increase¹.

However, you will earn that because the nuclear charge increases to a larger extent compared to the screening effect, the increase in nuclear charge outweighs that of screening effect, and the net nuclear charge increases.

Therefore, the size of an atom decreases across a period.

Yet down a group we have it differently.

This time, the size of an atom increases down a group because the screening effect due to an increase in the number of electrons or electronic shells greatly outweighs that of nuclear charge due to an increase in protons.

Confusing huh.

School Notes Can Be Confusing

Throughout my years of teaching, I have seen how JCs can sometimes de-emphasize important concepts while loading with irrelevant not-to-be-tested content.

Electrochemistry

It also doesn’t help when they choose to define anode to be positive while cathode to be negative².

These associations change depending on whether we have a galvanic cell or electrolytic cell.

Instead, students will remember better if you define anode as the electrode where oxidation occurs.

Likewise cathode is the electrode where reduction occurs.

This set of definitions is fixed whether you have a galvanic cell or an electrolytic cell.

Comparing instantaneous dipole-induced dipole attractions against permanent dipole-permanent dipole attractions

Often in notes if a compound has permanent dipole-permanent dipole (pd-pd) attractions it will omit to mention its instantaneous dipole-induced dipole (id-id) attractions to explain differences in boiling points.

Turn out that some students did not realize that all covalent compounds have id-id attractions by virtue of the electron cloud each molecule must possess.

Purely because the school lecture notes made no mention about it.

The fact that compounds possessing pd-pd attractions having highly boiling points than compounds having id-id attractions are only valid – if they have similar Mr, is not often mentioned.

That is why sometimes heavier non-polar molecules can having higher boiling points compared to polar molecules.

Handling Exceptions and Anomalies

Yet all the trends you have been painstakingly studying for so long is not always smooth and nice.

Exceptions are abundant in A Level Chemistry and all the theories and models don’t always work out well 100

When that happens, scientists have to understand the anomalies and account for the kinks.

Electronic Configuration

For example, one would expect the electronic configuration 3d orbitals to be filled before 4s.

But it turns out we have to fill in electrons for 4s before 3d.

“Okay, I can put up with that,” you said.

Except you start grabbing your hair after finding that you should be filling 3d⁵ 4s¹ instead of 3d⁴ 4s² for Cr and 3d¹⁰ 4s¹ instead of 3d⁹ 4s² for Cu.

No surprise students are complaining.

First ionization energies

The trend of first ionization energy (I.E.) is also not smooth sailing.

You are taught that 1st I.E. trends higher with a smaller atomic radius, as when you move across a period.

Yet in period 2, you have Be and O throwing spanner in the works.

Each carries different explanations for defying the trend, giving the poor student more things to remember – and frustrations³.

Covalent characteristics in ionic compounds and vice versa

You have been learning that metals and non-metals will form ionic compounds.

Then suddenly, AlCl₃ and BeCl₂ appear out of nowhere and you are supposed to know that they are covalent than ionic!

Such exceptions are more common than not.

And you wish if only your parents are reading this..

Deviation from O Level

Due to the need to introduce chemistry to the masses, certain concepts in O Level can be overly simplified or at worst misleading.

Shapes of molecules and dot-and-cross diagrams

In O Level, you are learned to draw dot and cross diagram, where pairs of electrons are drawn in fixed positions.

The concept of attaining a full octet structure also confuses A Level students when they are exposed to elements with the ability to expand their octet structure and accept more than eight electrons.

Furthermore, the notion of s, p, and d orbitals with their respective 3D shapes also doesn’t sit well with 2D fixed electron dot and cross diagram.

In A Level, students are also exposed to the Valence Shell Electronic Pair Repulsion (VSEPR) theory to determine the shape of the molecules.

What complicates matters is that due to lone pair-lone pair repulsion > lone pair-bond pair repulsion > bond pair-bond pair repulsion, the bond angle is not always consistent.

If you have been studying diligently you will know what I mean.

Acids and bases

Instead, now you found that the definition of acids learned in O Level is very limited. Why are compounds such as NH₃ a base when no OH- is emitted is also not explained?

It is also the most outdated among all three definitions.

Arrhenius theory, the one you learned in O Level is formulated in 1884!

While both the Brønsted-Lowry theory and Lewis theory are proposed in 1923.

Electrolysis

At the O Level, it is usually conveyed that the electrolysis of water involves the discharge of H⁺ and OH^– to make the understanding of the electrolysis process easier at O Level, the concentration of the two ions in pure water is actually very low.

Therefore, this understanding is inaccurate.

At A Level, you are taught that H₂O is being discharged instead.

P. S.

If you do want your parents to know your pain in understanding Chemistry, make sure they read this.

Your friends will want a copy of this article, make them ask for it.

Notes:
1. Some schools will indicate that the screening effect is approximately constant.
2. For electrolytic cells. For galvanic cells the polarities are reversed.
3. The electron is to be removed from the 2p orbital in B and is further away than the 2s orbital in Be. Therefore lower energy is required to remove the electron from B. For O. due to inter-electronic repulsion, it is easier to remove an electron from here as opposed to the 2p orbital of N which has only one electron.