Chemistry

Welcome to the Chemistry section of this non-exaustive wiki to the ITA/IME college entrance exams I've made as a tool to futher my progress towards my goal of getting in! Here, we should cover quite a wide array of topics!

I began studying Chemistry around January 2025, about 6-7 months ago, and finished all the FB Online lectures for it this week, thanks to the Lord. I hope to read some complementary books soon, but, preface aside, here are some of the things I've learned.

Thermodynamics

An intresting preface: Personally, as an unqualified individual with ready access to the world-wide web, I think that just as physics can sometimes be thought of as applied mathematics, Chemistry, for a large part of it, is largely thermodynamics.

From what I've seen, there's a lot of insight to be gained from this one subject, so I find its thorough and comprehensive understanding quite important if you are to fundamentally capture the concepts in later sections. I may be incorrect, but the ability to model physical systems like molecules with a basis in energy lets you, at its core, acquire a vast degree of knowledge on the probablities and seeming inevitabilities of the subject, be it through expected bonds or equillibrium states of many kinds.

The subjects of equillibrium and solubility (which can go hand-in-hand) are very dependent on this in particular for certain analyses.

Laws of Thermodynamics:

If we talk about thermodynamics, it's helpful to get its basis out of the way. While I won't cover the rich and contextually important history that leads to many of these understandings and aids in the proper comprehension of the subject (I strongly advice reading into this!), I hope to cover some more basic fundamental ideas that are sufficient to be used in the understanding of larger and more complex models through the lens of abstraction.

What we would like to do in this section is show many of these relations we can make, but in order to do that, its relevant to talk about the so-called laws of thermodynamics, starting not with the first but the zeroth law: the transitivity of temperature.

Zeroth Law: Temperature and Transitivity

Put very briefly, we know that molecules and particles can become agitated. We will now create a property called temperature to set values relating to this measure of agitation. There are many ways to measure the value of temperature for an object, but the Celcius, Farrenheit, and Kelvin scales are the most common. If you plan on taking this test, it seems you are to familiarize yourself with freely converting between all of these by yourself; be careful! Amen

Historical Footnote and Fun Fact: The Farrenheit, despite rightly critized for its non-comformance to SI units, has a wonderfully rich history! I don't remember all parts of it, but on research I found that it's baseline zero point was chosen as the freezing point of a stable brine solution, which made measuring easier than with water at the time!

Aside from this, unlike the Celcius scale which sets the boiling point of water as a target, the target for Farrenheit was 96 degrees for the standard body temperature (which, with later, more precise meaurements, is now closer to 98.6 degrees Farrenheit, about 2.6 degrees off, which was not bad!). 96 was chosen instead of 100 because it is the sum of 64 and 32, two powers of two, which made finding it with bisections easier.

Overall, despite the many criticisms, I find joy in looking at the historical and experimental reasons/considerations that made this wonderful scale come to be :) OH! DID I MENTION IT HELPED DEVELOP THE USE OF MERCURY FOR CALORIMETRY??

No matter what scale we use to measure this property, the zeroth law of thermodynamics simply states that for any object A, with a given temperature \( \theta_A \), if it is in thermal equillibrium with another object B--which is to say, they have the same temperature, aka \( \theta_A = \theta_B \)--that is itself in equillibrium with yet another object, C, A will be in equillibrium with C, thus making temperature transitive. This is the basis for a lot of things, and while it might seem self-evident, many things in nature don't follow this pattern so its interesting to note!

General Concepts and Quantitative Figures:

Calorimetry

Using Heat in Chemical Scenarios:

Atomic Understanding Of Matter

Atoms are a funny thing. From a young age, I was taught about them, but while the concept seemed so close to my grasp, it was seemingly out of reach.

The questions I had and pondered on were left unanswered by my limitations and lack of study in the study:

"So... atoms exist... but how small truly are they? How is it they precisely interact?" --and maybe the most interesting of these questions:

"How can I use this framework to draw further understanding and semi-acurately model physical scenarios in a logical and methodical way?"

Regardless of your stance on my normalcy as a child (or onwards), I think there is much to appreciate about the atom. In this section, we aim to cover some theoretical bases and the historical building blocks that have allowed for the more-detailed comprehension of our world we have today.

Historic Analysis:

The first to be recorded as discovering the atom--or its concept--date back to Greek philosophy, some 2,000 years ago, around the time of our LORD Jesus Christ--many years ago! From that point onwards, matter was thought to have an indivisble smallest unit.

Dalton, however, expanded and experimented on this idea, parting off the work of Joseph Proust and his law of definite proportions, which observed that a given substance or compound, regardless of volume or other properties, has a fixed mass ratio between its elemental consituents.

From this, alongside formalizing concepts about the atom (still maintaining that they were indivisible, which was later found to be less-than-completely-accurate), he observed another pattern: the ratios between substances composed of the elements typically are some fraction greater-than or less-than one with small whole numbers. More simply, we can observe that they usually vary relatively uniformly to what we've grow to expect working with molecular notation (CO2 and CO, for example, where we would expect the ratio between the first and second mass ratios of each of the molecules to be 2). This law is later dubbed the law of multiple proportions.

Periodic Properties and Table:

Upon the discoveries made which led us to the current, most-commonly-accepted representation of the atom for practical purposes today, more insight was also given into the relationships between them. One handy way to group atoms is the period table--a concept that has seen many reenditions over the years but has been rather ubiquitous in its current form for the last century or so.

Notably, the concept of a periodic table came before the existence of theory sufficient enough to explain the electronic effects responsible for the similarities between certain atoms, however, despite being arrange merely based on emperical data, there is a remarkably close correlation between it and certain key properties that explain this phenomenon.

Starting with groups, the table is arranged in several collumns and rows. We call each collumn a group, and we see that they tend to have similar properties. When looking at the electronic distribution for them, we see this appears to be no mere coincidence: groups have a common characteristic within their members being that they all share the same number of valence (or outer-most) electrons. These electrons are specifically the most relevant ones because they typically have substantially higher energy levels than their inner counterparts.This way, we observe that the period table is divided into groups of the same number of valence electrons on the vertical, changing mostly their mass through proton and neutron count heading down.

On the horizontal we have periods or rows, which show a different pattern. Sequentially speaking, each atom in a period has exactly one extra proton and one extra electron in its neutral state. As such, we see that the mass for periods also increases in a direction, this time left to right. Note: It is worth noting that each period also corresponds to a valence layer or shell number, increasing downwards.

Beyond this property, it is also worth examining the periodic table in terms of a nother wildly influential property: the atomic radius (defined by half the distance between two nuclei of the same atom, be it through covalent or ionic bonds with eachother, giving the adjective assigned to the property) is somewhat counterintuitive. As a whole, we notice that groups tend towards bigger radii as they descend further down, however periods tell a different story. One of the factors influencing the radius of an atom as defined through this is the extent to which their electrons expand to; for our purposes, we see that electrons in lower shells/layers of the atom contribute to an effect we call shielding, in which the charge of the electrons effectively counteract that of the same number of protons in a nucleus when found between the electron in question and the nucleus. As such, with less of an attractive force, we can imagine that the electron has more space to roam, thus yielding a higher radius despite the physical bulk expected from the extra matter at its core.

Because of this, we see one main pattern: as the number of proton increases within a period, the atomic radius decreases. We can explain this further looking at two cases. Consider Lithium (z=3) and Fluorine (z=9). As both are on the second period, we know their valence electrons also lie on the second shell. Belonging to family IA, Lithium has an electronic distribution of [He]2s¹ and Fluorine [He]2s² 2p⁵. We can calculate the effective charges for an electron on both of them like so: z_effective = 3 protons - 2 shielding electrons in the core = 1; z_effective = 9 protons - 2 electrons in the core = 7. Here, the pull on the electrons of the Fluorine atom is far stronger than that of the Lithium atoms, thus yielding in a tighter radius.