General Chemistry for Everyone!

Hi! I'm a college student and I've been tutoring general chemistry for 2.5 years now. I adore it, I want to write a book about it, but what I care most about is making chemistry knowledge accessible, digestible, and fun for everyone! I'm in the process of writing said book, but I'll be posting snippets here to keep myself accountable and to put relevant and fun chemistry help here. I'll be updating as often as I can, and I'm also open to questions!

Ok so if my last post seemed a little unrelated to chemistry I promise it's related! I just wanted to separate it into two sections so it wasn't like a billion words.

We're gonna start talking about orbitals real soon, but for now, all you need to know is that electrons can occupy a variety of different energy levels. These energy levels are stairs, not a ramp. It can be at level 1 or 2, but not 1.5. Also way more than two, but the point is there are fixed energy levels and electrons can be at any of them, but not between two of them. If you put energy into an atom, you can make an electron jump up a few levels. It's not too stable there, so it stays briefly before falling back down. It can fall to any level below it that has room, not just the one it started at, but it has to eventually get back to where it started, the lowest energy level it can occupy, called the ground state. If it goes from level 1->3, it can go back as 3->1 or 3->2->1. For each of the jumps back down, it releases energy in the form of a photon. The total energy gained should equal the total energy lost, whether that was in one step or multiple steps added together. The amount of energy lost determines the wavelength and frequency of the photon it emits.

Energy absorbed, electron goes up in energy levels. Energy lost/emitted, electron goes down in energy levels.

Hey hello I had a section I was planning to do before this one but I got a little overwhelmed by the volume of content and also it's not the most important especially before we get into orbitals, so I'm doing this first. Btw the missing section is an atomic meet and greet, lmk if there are any specific elements you want to see covered in more detail! Otherwise I'll just ramble about my favorites mostly.

Ok so electromagnetic radiation! They're waves in the electric and magnetic fields, parallel to one another.

Wavelength is the distance between the peak of one wave to the peak of the next. It's measured in meters or a derivative of meters like nanometers or millimeters. (Also I want some input, would you want an overview of SI units?)

Frequency is how many times in one second the wave passes through a given point. It's measured in Hertz (Hz), which is the same as /sec. So 5Hz is 5 waves per second. In a physiology class I once took, we did a cool experiment where I got to put a grounding electrode on the back of my hand and take an electrode probe and find a nerve in my arm. It made my fingers curl in involuntarily, which was such a weird feeling. Higher voltage electricity felt more intense but wasn't painful, but the higher frequency electricity really Hertz. (I'm sorry. It's not a good joke. It is true though!)

Higher frequencies have higher energy and shorter wavelengths. Low frequencies have low energy and long wavelengths. All EM radiation travels at the speed of light. If I could walk across a 30 meter room in 30 seconds, taking 1 step every second and each step is 1 meter, I am going the same speed as my (much taller) friend, walking across the same room in the same amount of time, taking a 2 meter long step every two seconds.

Speed - both 30 meters/30 seconds, or 1 meter/second

Frequency - Mine is 1 step/second, his is 1 step/2 seconds

Wavelength - Mine is 1 meter, his is 2 meters.

Energy - (Humans are not a good example since living systems are eo complex in energy, but bear with me.) I'm stepping more frequently than he is, each step takes the same amount of energy. I use more energy than he does to walk across the room.

(Another tangent, this is my example because radio waves are part of the EM spectrum and said very tall friend was the person who encouraged me to join him in getting licensed to operate ham radios!)

Ok listen, it's late at night for me and I should be sleeping. However, I thought I should make a master list of study tips because that's a huge part of what I teach. Most of my students are in their first year of college, so a lot of them want both chemistry content help and help navigating college courses. All my training is about both of these. These can be applied to studying literally anything. I use these all the time in my own classes. Enjoy!

First of all, your brain only functions when your body does. It is almost never a good idea to stay up all night before a test to study, the consequences of being tired almost always outweigh any benefits of extra study time. Also, your brain needs food and water and sunlight and social connection to function. Those are important. I beg of you, eat an actual meal prior to your exams.

Your brain remembers weird stuff better than normal stuff. I come up with wacky, out-there examples because they stick better in my brain. 'BrINClHOF' is a series of letter, but 'Have No Fear Of Ice Cold Beer' is an actual, somewhat strange, sentence. It sticks better. (It's for diatomic elements btw!)

For the studying part. Use the study cycle. This has been thoroughly researched and it works. Take an hour, spend the first 5 minutes setting goals, the next 40ish minutes studying, then take 5 minutes to see if you accomplished the goals, then 5-10 minutes of a break. The break should be something relaxing, stay off social media, call a friend, take a walk, have a balanced snack, etc. Repeat as needed. The studying part of studying should be active, not passive. Passive studying is reading notes or a textbook, highlighting notes, or watching videos. Active studying is working on practice problems without a key or example in front of you, rewriting concepts or definitions without notes then checking them, teaching someone else (it can be a person/plant/stuffed animal/imaginary audience/pet/whatever) the concept and fielding their questions, drawing diagrams to explain topics, or even researching examples of a topic and trying to come up with a reason for why it is the way it is.

Researched along with the study cycle is a method for learning that works wonders. Preview, class, review, study. If your instructor has the topics for the next day in class, notes, homework, or something like that available, take time before class to look over it. Make a mental or physical note of what you do or don't already understand. Write down questions you have, and in class try to answer them. Familiarize yourself with vocab terms and key concepts. In class, actively take notes. Don't write down what is said word for word, put it into your own words. I obviously have some unconventional ways of thinking about things, use the comparisons your brain makes and understands. If you have the chance to interact with other students in discussions during class, take initiative and teach others what you know well, and ask about the things you don't understand. Form study groups with other students so you can teach each other and have motivation and accountability to study. After class, before the end of the day, take 5 minutes to jot down key points from class without looking back at your notes. Also make note of the concepts you still need more work on so you can focus on those during your study sessions.

Study in short bits often, rather than taking a huge chunk of time right before a test. It just works better.

For any and all math within a science class, start by identifying the equation(s) needed. Identify the units of each part. Ensure units cancel to your desired answer's unit. If not, convert some stuff. Rearrange equations before you put the numbers in. Keep every number with its unit, and write every single unit. It feels tedious, but probably 2/3 of the math mistakes I see in my students' work is because they had the wrong unit, didn't keep a number with its unit, or something along those lines. It's tedious and boring, but solving an equation shouldn't have surprising and unexpected results.

Along the lines of math, always practice and do homework with the calculator you are allowed to use for the test. You don't want to show up to the exam and not know how to use your calculator. It sounds like common sense but I've had students ask me right before an exam how to use their calculator. That is something you shouldn't make yourself expend mental energy on.

If your mind tends to wander like mine does, try keeping a blank notebook/sketchbook/paper next to your actual notebook/note-taking device. I like to doodle and write down whatever my mind wanders to there so my notes stay neat and focused. Bonus if your brain connects the concepts you learned to the doodles you did. This also helps since I'll come up with tangential questions or ideas from the lecture, and if I write them down my brain doesn't have to split its focus between remembering the ideas/questions and learning the content.

Go to office hours if they're offered and you have the time! If you're struggling, your instructors are there to help. If you're doing well, you can get extra practice, additional resources, or talk to your instructor about the stuff you find interesting in the course. When I took introductory chemistry, I didn't have time to go to office hours, but talking to my professor after class about the questions I had and the things I thought were interesting from class led to him suggesting I tutor for the class, which you can tell is my absolute favorite thing to do!

Ionic radius

Ionic size trends start off the same as atomic radius trends, but then they change. (Yep. Good work me.) Ok, so you need to understand what an isoelectronic series is. It’s a series of ions that all have the same number of electrons. They’ll have consecutive atomic numbers, usually with a noble gas in the middle. Most main-group ions (everything but the transition metals) form ions to be isoelectronic with a noble gas, since a full valence shell is the most stable configuration. Ions in an isoelectronic series will always follow the same relative size trends. If we have +2, +1, 0, -1, and -2 ions, 0 is in the middle, with +2 as the smallest and-2 as the largest. I like to think about this in a very anthropomorphic way. Tangent incoming! My partner and I have a friend who fosters kittens. We like to come over and play with the kittens because hell yeah, kittens, but also because it’s good for them to socialize with new people. When my partner and I were hanging out with one particularly energetic litter, I realized kittens are a fantastic metaphor for electrons. Both are tiny, fully of energy, and running around everywhere randomly. If there are two kittens in a litter and two humans cuddling them, we can keep them mostly in control. Two humans and one kitten? That baby is staying exactly where we want it, no mischief for that kitten! But 3, 4, or more kittens and only two humans leads to utter chaos. If protons are the humans, electrons are the rowdy kittens they’re trying to keep in one place. One proton per electron? All good, nice and contained. Medium ionic radius. More protons than electrons and those suckers are sticking in super close. Tiny ionic radius. A lot of electrons and not too many protons leads to the electrons zipping around everywhere. Huge ionic radius. Makes sense?

Ionization energy

More anthropomorphization. Way more. Sorry. Back to the kittens! If I have a ton of cats and I love cats, and someone wants to adopt one of my cats away from me, I’m gonna ask for a lot of money if I accept it. Electronegativity in this case is analogous to loving cats. If an atom with high electronegativity is ‘asked’ to give up one of its electrons, it requires a lot of energy (the currency of the chemical world!) to give it up. This trend follows essentially the same pattern as electronegativity, the top right corner has the highest ionization energy, and the bottom left corner has the lowest. As a definition, first ionization energy is just the amount of energy required to take an electron off a neutral atom. I mentioned first ionization energy. You can have as many ionization energies as there are electrons in the atom. This is useful for identifying an atom. Given a series of ionization energies, you can figure out the group an atom is in. When you find the big jump between ionization energies, that’s where it switches from taking off valence electrons to core electrons. The number of ionization energies before the jump is the number of valence electrons, which translates to the group number. The subsequent ionization energies increase, going back to kittens we can add to the metaphor. If I already had to give up one cat, I’ll be much more reluctant to give up another one. It also makes sense with the idea that the universe doesn’t like charges. A charged particle would be more stable reducing its charge, rather than increasing it.

Electron affinity

The trends for ionization energy and electron affinity are the same, even though they are essentially the opposite reaction. If ionization energy is the amount of energy required to take an electron off an atom, electron affinity is the amount of energy released when you add an electron to an atom. If energy is the currency still, electrons are kittens, and electronegativity is loving cats, electron affinity is how much I would pay to adopt another kitten.

I'm realizing now that a few basic vocab terms may be useful.

Atomic number = number of protons

Atomic mass = number of protons + number of neutrons (we assume protons and neutrons have a weight of 1 atomic mass unit, or amu, each, and electrons have negligible mass.)

Elements, like us, can’t resist a good trend. Unlike us, they physically cannot resist a trend. This is one of those things that you can just memorize, but I personally think it’s easier to understand the underlying reason.

Electronegativity

… how do I explain this without too much physical chemistry? Probably by ignoring it. For electronegativity, I’ll give the definition and the rule. If you want a better explanation, let me know and I can do my best to explain it, it may have to involve some physical chemistry. Electronegativity is the tendency of an atom to pull electrons towards itself. This is relevant in chemical bonds, but also it can be helpful for remembering atomic radius later on. Remember than fluorine (my favorite element!) is the single most electronegative element. As an element gets further from fluorine on the periodic table, it gets less electronegative. Scoot hydrogen a little bit, but it’s pretty much solid to remember it that way. The transition metals also get kinda weird, don’t worry about them for right now.

Shielding

Imagine a bonfire with concentric circles of people standing around it. If the nucleus is the fire and the electrons are the people, this is a good metaphor for shielding. The stronger the nucleus (more protons), the larger and hotter the fire is. The farther out the valence electrons are from the fire, the more rows of people are between the valence electrons and the fire. If you’re far out, you’ll feel colder, but the same distance out with a stronger fire, you’ll feel warmer. So. The ‘warmer’ an electron ‘feels’, the more tightly it’s being pulled towards the nucleus. As you move from left to right, the valence electrons are the same number of shells out from the nucleus, but the nucleus keeps getting more protons. Someone standing next to you around the fire doesn’t diminish the heat you feel, just how more electrons in the same shell don’t really shield one another. The whole shielding effect comes from protons attracting electrons, and electrons repelling other electrons. It’s also related to the distance and attraction curve. Just like magnets, the farther opposite charges get, the weaker the attraction is. Weak attraction between the nucleus and electrons keeps them farther apart, and the farther distance weakens the attraction. Weird. Let’s head out before the chemistry gets too far into physical chemistry.

Radius (Size)

One over is nitrogen’s group, the pnictogens. They usually form anions, with -3 charge.

Next is the chalcogens, oxygen being the first. They form -2 charged anions.

Halogen time! These are right before the noble gasses, they only need one more electron before getting to a full valence shell. They’re also super reactive, and they’re typically found as diatomic elements, in their standard state at 25°C and 1 atmosphere of pressure they have a buddy of the same element. They move in groups of two because of how reactive they are, they’re very unstable if they’re separated. Think of them as having separation anxiety, except if they’re alone, they’ll rip up your lung tissues instead of feeling anxious. Like chlorine gas! Unpaired electrons are really unstable and reactive (we’ll talk about it more later), so molecules or atoms with unpaired electrons are called free radicals. Lots of people like to use this term to sell blueberries. Free radicals are super reactive, so the organic molecules in our tissues can be altered or destroyed due to what’s called oxidative stress when exposed to a high level of free radicals. In high concentrations, this can lead to severe tissue damage, like the chemical weapons chlorine gas and bromine gas. They damage molecules in your cells, eventually ripping apart the delicate thin tissues of the alveoli, which means your body can no longer exchange oxygen and carbon dioxide to your blood cells. The tissue damage also fills the lungs with blood and bits of tissue. Not very pleasant. Antioxidants, such as those in blueberries, have molecules that can react with free radicals to create more stable radicals, like carbon ions. They still are reactive and unstable, but far less that in the free radicals. The molecules are also larger and can be bound to even larger molecules and excreted safely from the body. There’s also some evidence that long-term exposure to low levels of free radicals can cause oxidative stress that compounds over time, eventually leading to cellular damage and cancer. So. Blueberries might not be a bad idea every once in a while. I’d still recommend a gas mask for chlorine gas though. I have a further tangent about chlorine gas, but I’ll save it for later when we talk about light.

Moving down a row, we meet lithium and beryllium cuddling up in columns (or groups!) 1 and 2. Both are metals. Moving across to boron, we find some discrepancies in how groups are numbered. The total width of most tables is 18 blocks, but it can be extended out to 32. The ‘moat’ under the table of lanthanides and actinides really should be put back in the middle, but that makes it way too wide for the formatting most publishers like. Oh well. Because of the block of transition metals, some periodic tables number the group boron resides in as 3, and some label it 13. Either way, boron. 3 valence electrons, 5 protons, 5 total electrons. Next is carbon, very relevant if you like living beings on Earth. Then it’s nitrogen, oxygen, fluorine (my favorite!), and our next noble gas, neon.

Let’s save further introductions for later. For now, a few groups that are relevant!

Hydrogen is in the alkali metal group. They like to lose one electron to form cations with a +1 charge, and they react violently with water. Other than hydrogen, a few notable members are lithium, sodium, and potassium.

Next are the alkaline earth metals. Beryllium, magnesium, and calcium are the first few. They tend to form cations with a +2 charge by losing two electrons.

Groups 3-13 are transition metals. Many general chemistry classes don’t talk about them too much, they can do a lot of weird things that make more sense after we go through orbital theory. Most metals that are commonly thought of as metals are in this category, like iron, nickel, and zinc. One fun column has copper above silver, which is above gold!

After the transition metals, we get to boron’s group, which is creatively called (drum roll please,) the boron group. Wow. Revolutionary. They’re sometimes called earth metals too. They have some interesting properties, which will make more sense once we cover the octet rule. If they form ions, they form cations with a +3 charge.

Now that we know about protons, neutrons, and electrons, we can get into atoms! The identity of an atom is fully dependent on the number of protons. The number of neutrons determines which isotope it is. Carbon-12 and carbon-14, for example, are two isotopes of carbon. Carbon-14 is heavier, but chemically acts the same as carbon-12 since the number of protons and electrons is the same. If there are a different number of electrons, it’s an ion. More electrons that protons is a negatively-charged anion, fewer electrons than protons is a positively-charged cation. My trick to remember these is the cations are pawsitive. To make this image a bit more vivid, I think of my cat, Luna. If I had a giant atom, she’d jump on top and knock a few electrons off. Cations, am I right? If altering the neutrons makes an isotope and altering the electrons makes an ion, what does altering the protons do? It changes the element!

There are 118 elements on the current periodic table. There may be more that exist, but we haven’t found them yet. Each one has one more proton than the previous element. Hydrogen is the ‘simplest’, having one proton. A few isotopes of hydrogen tend to exist, usually including zero, one, or two neutrons. (Also called protium, deuterium, and tritium. Tritium is radioactive, and has been used by the US military to make glow in the dark faces for compasses. I have one!) In its neutral state, it has one electron. It can either form a positive or negative ion, the anion typically being called hydride, and the cation being just a proton. Hydrogen is also the model we use to study electron orbitals. We’ll discuss that more later, it gets into some weird physics.

So. Building blocks of the universe. Protons, neutrons, electron. Electrons are… whatever the hell they are. Protons and neutrons are made of quarks, whatever the hell those are. The math works well, both are made of 3 quarks, in different combinations of up and down quarks. Up quarks have a change of +⅔, down quarks have a charge of -⅓. Protons are two up and one down quark, leading to a net charge of +1. (⅔+⅔-⅓=1) Neutrons have two down and one up quark, so they have an overall neutral charge. (⅔-⅓-⅓=0) Electrons have a charge of -1. What is charge? Don’t worry about it. For general chemistry, know that positive and negative charges attract, and generally having a charge is more unstable (more on stability later), so charges should balance if possible. As a sneak peek into the elements, here’s a baseline rule: atoms are neutral unless we call them ions, for an atom to be neutral the number of protons must match the number of electrons. Neutrons, seemingly in the atomic cuck chair, do not contribute to charge balancing. They primarily help with atom stability. They do this because of another fundamental property of charge: repulsion. If opposite charges attract, like charges repel. You can think of it like magnets. The north pole of one magnet attracts the south pole of another, but repels another north pole. You can also think of it homophobically, but I ask you don’t. (You see the metaphor right?) Anyway, neutrons give protons some space, so their repulsive forces don’t explode the nucleus before it can even form.

Me: Dad, what are bricks made of?

My dad: Clay, mostly.

M: What’s clay made of?

D: Largely silica.

M: What’s silica?

D: Silicon and oxygen.

M: What are those made of?

D: Protons, neutrons, and electrons.

M: What are those made of?

D: Protons and neutrons are made of quarks.

M: What are those made of?

D: We don’t know yet!

M: Why don’t we know?

D: Scientists haven’t figured it out yet.

M: Oh.

This is perhaps the most accurate explanation of why I am the way I am, psychologically. I would ‘play’ this ‘game’ over and over for a few months, always hoping this time would be the time we (as a species, I suppose) knew what quarks were made of. I still haven’t gotten a good answer. Reminiscing on this on a long drive with my dad, I discussed my pet theory that quarks, or whatever quarks are made of if there are more layers, are made of ‘bubbles’, overlaps, or sections of interacting universal fields. He agreed that it could be plausible, but to be honest, almost anything is. To complicate matters further, we can look at electrons. Many interesting theories have been developed about electrons, probably because nothing about them makes sense. When researches shoot a bunch of them through a slit pattern, they form a wave interference pattern. Fine, light does that too. So electrons are waves? Yes, no, and maybe. You can also send them through one at a time. They act like particles. Light can do that too. But! Individual electrons end up in one place like a particle. When you do a bunch of individual electrons consecutively, they form… a wave pattern. How? No one knows. One theory is that electrons can move through dimensions of time, past and future electrons add interference to current electrons. Another theory, though not widely believed, is that only one electron exists in the universe. This, in a way, aligns with the time-traveling electron idea. If there is only one electron, it has to occupy different roles at one time (or in an infinitesimally short time frame) in order for the universe to work that way it does. This doesn’t fit most of the other identities of electrons though, so it doesn’t seem to likely. Also, despite what the law of conservation of matter may assert, electrons (which do have mass, though for the purposes of atomic mass calculations, is negligible compared to protons and neutrons) can temporarily cease to exist. When a HUGE amount of energy is applied to an electron, especially one in a very high energy level already, it can be briefly turned into a photon, which does not have mass. Where does the mass go? Where does the mass come from when it reappears? Where did you come from, where did you go, where did you come from Cotton Eye Joe electron mass?

Alright. Chemistry tends to be an intimidating subject for many, but I promise it’s not too bad. A few things to note before we start, however:

Some ‘truths’ taught in general chemistry classes are wholly untrue, and many more are partial truths or educated guesses. I say this not to disparage your chemistry educators, but rather to explain that much of what is taught in general chemistry courses is an approximation of the truth, rather than the truth. To be entirely honest, many of the problems posed by chemistry at a fundamental level do not have answers that align with the current understanding of physics, and for that matter, the universe. Our guesses, approximations, and lies do in fact serve a purpose. A great deal of the important part of how chemistry works for the average person can be explained with adequate truth this way.

Related to the above point, I will not go into too much physical chemistry. Some relevant points may be mentioned as appropriate, but alternatives can also be provided. While I personally prefer to learn by understanding the underlying causes, it can still be perfectly fine for daily use to only memorize what happens, rather than why it happens.