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Matter is something that occupies space and can be perceived with human senses, and mass is a measure of the quantity of matter in a material. Chemical reactions obey the law of the conservation of mass, so the total mass in a system remains constant during a reaction.
Matter that can be separated by physical processes such as distillation, chromatography, or filtration is a mixture, which may be homogeneous or heterogeneous depending on uniformity. Mixtures are comprised of various different pure substances, which are a type of matter that cannot be separated into other substances physically. These can be classified further into elements when even chemical processes cannot break the matter into simpler components; otherwise, they are compounds – two or more elements bonded in fixed ratios. Compounds have a specific chemical formula.
Matter is made up of atoms, the center of which is a positively-charged nucleus of positive protons and chargeless neutrons. Each element has a different amount of protons known as the atomic number, and different isotopes of an element have variable amounts of neutrons. The mass of atoms and subatomic particles is measured in atomic mass units (amu). Periodic tables will also show the average atomic mass of an element, or a weighted average of all its isotopes. Elements in the same row of the table are in the same period; elements in the same column share a group. Noble gasses are the very last, 18th group on the table and are rather unreactive due to having full shells of electrons. On the other hand, halogens are the very reactive 17th group. You'll also find most metals within the first twelve groups of the table.
Atoms that gain or lose electrons are known as ions and have a charge. Cations are positive and have lost electrons; anions are negative and have gained electrons. Distance from the bookend groups of the table can make for a reliable indicator of ionic charge; halogens have -1, Group 16 usually has -2, and the most noteworthy elements in Group 15 usually have -3. Meanwhile, the first two groups are +1 and +2, respectively.
You are expected to memorize certain polyatomic anions in chemistry because of how frequently you will come across them. Here's a table of them so you don't have to.
| Name | Formula |
|---|---|
| Ammonium | NH4+ |
| I'M WORKING ON THIS STILL | LAZY WHEEE TBD WIP TKTK ETC. |
When expressing quantities of atoms/molecules in a chemical reaction at a macroscopic level, you want to use the unit known as a mole. One mole is 6.022 × 1023 particles, also known as Avogadro's Number (NA). When you interpret a chemical equation and see a coefficient in the very front of a component, interpret that as the amount of moles present. You are expected to use these to balance your equations - that is, the reactants should have just as many moles of oxygen as the products do. It helps to do this by focusing on carbon and oxygen first!
You're also expected to be able to convert from moles to molar mass, the mass in grams of one mole of a substance. For example, one mole of oxygen is about 16 grams. A the mass of a mole of CO2 can be found by determining that of one mole of carbon and two moles of oxygen, then adding them together. This makes the molar mass of CO2 about 44 g/mol.
When you understand moles, you can determine the limiting reactant in an equation, the one that is completely consumed by the reaction and determines the highest theoretical amount of product you can form. To find what that would be given your supplies, determine how many moles you have at your disposal, then divide that by the substances' coefficients in a balanced equation. The limiting reactant will yield the smallest dividend.
In reality, however, your reaction may yield less product than it theoretically could due to conditions affecting reactivity (more on that later). You can determine the percent yield you got by dividing the actual yield by the theoretical yield. If this number is higher than 100%, you have either done the impossible by creating matter out of nothing and should therefore pursue a Nobel Prize... or done something wrong with your math/reaction.
These reactions occur thanks to bonds and electrons. Each atom can have up to four electron pairs in its outermost valence shell (known as an octet), though there are exceptions, like with hydrogen and helium that can only squeeze in one pair (a duet). When an atom doesn't share its pair of electrons with another, that's a lone pair. When an electron doesn't exist in a pair, it's a radical.
You can expect to find electrons in an atom's shells, which are spherical regions around the nucleus. Larger atoms have more shells. When an electron moves to a shell further from the nucleus, it has absorbed energy, and when it falls back closer to it, it releases it, sometimes in the form of visible light. Shells can be divided further into orbitals. Each orbital can have two electrons, and may have forms that are not necessarily spherical (such as that of a dumbbell). A quantum number is used to describe their motions and shape. These suck and I need to study them more myself. Worth noting is that an electron is simply "likely" to be in a given orbital, but not guaranteed! This is because physics is work of the fae and there are stupid rules to everything.
Many different kinds of chemical bonds can form between atoms when orbitals overlap. These are electrostatic forces that hold the atoms together. Covalent bonds are composed of atoms sharing an electron pair. Their orbitals overlap. You'll see these most frequently. Single bonds share on pair of electrons and they are sigma. Double bonds share two pairs, triple bonds share three pairs and are the strongest of the covalent bonds, and each of these extra electron pairs is pi. Ionic bonds are typically stronger than covalent bonds because they form between two ions of opposite charge. Hydrogen bonds are weaker, more like polar interactions than strong chemical bonds. These occur between hydrogen atoms and oxygen, nitrogen, or fluorine atoms, such as between two water molecules.
ඞ im sigma
and im pi ඞ
🔥 THE MATHPLANET BROTHERS 🔥
Different elements have different electronegativities, different tendencies to attract electrons. A trend worth keeping in mind is that fluorine is the most electronegative element of all, and that elements become less electronegative the further away they are from it on the periodic table. When two bonded atoms have a major difference in electronegativity, they also have a higher dipole moment - a fancy way to just describe the difference of charges. A higher number of bonds also tends to increase the dipole moment of a molecule. Within a molecule, it's also worth keeping in charge the formal charge of an atom. This is the difference between its valence electrons and the electrons it "owns" (that is, one per bond, plus both in a lone pair). Remember that atoms "want" the electron configuration of a noble gas, typically eight in the valence shell (octet rule), but there are exceptions if there aren't enough total electrons to go around - and this trend applies most to second period.
VSEPR, or Valence-Shell Electron-Pair Repulsion, is the theory that electon pairs geometrically arrange themselves around atoms in a way that minimizes repulsion energy. It can be used to determine how electrons and atoms arrange themselves within a molecule. It helps to memorize electron pair geometry first. Molecular geometry is usually "the same" as electron pair geometries with the same steric number (number of atoms bonded to central atom + number of lone pairs on central atom), but some "spaces" around the atom are "invisible" electron pairs.
| SN | Electron Pair Geometry | Molecular Geometry |
|---|---|---|
| 2 | Linear | Linear |
| 3 | Trigonal planar | Trigonal planar, bent |
| 4 | Tetrahedral | Tetrahedral, trigonal pyramidal, bent |
| 5 | Trigonal bipyramidal | Trigonal bipyramidal, seesaw, T-shaped, linear |
| 6 | Octahedral | Octahedral, square pyramidal, square planar, T-shaped, linear |
TKTK: Gasses, formulas + pressure
TKTK: Liquids, solutions, saturation, solvent vs solute, aqueousness, solubility, dilution equation, ionic theory + electrolytes, jump to gen-6
TKTK: Solids, jump to gen-3
TKTK: The actual geometry/VSEPR stuff.
This covers energy and kinetics
This covers light and waves and stuff.
This section covers acids, bases, pH, and the like.
When an acid does its job, the acid becomes more negative.
This covers redox, electricity, etc.
This is the fun stuff.
Jump to... Introduction / Funtional Groups / Stock Reactions
Organic chemistry focuses on covalent bonds, for the most part, and the element of carbon. However, electronegativity, polarity, and the like remain pretty relevant. If you're reading this section, you better hope you understand the first half of this page. As this subject was taught to me, a lot of it was just being able to memorize/improvise chemical reactions, so get ready to be doing that.
As you should know, things in the universe want to be of lower energy. They want their charge to be neutral or dispersed, they want a more neutral pH, they don't want geometric tension.
| Name | Formula |
|---|---|
| Anotha one | NH4+ |
| filling this out | is going to suck so bad |
TKTK: Previous eighteen chapters.
Acyl compounds resemble a carbon attacked to another functional group, an R group, and double-bonded to an oxygen. They are a broad category, and include the ones into which I will get into detail below. The more stable they are, the less reactive. Acetyl halides (contains a halide) are very reactive, followed by acetic anhydrides (resembles two ketones joined by an oxygen). The most stable of them is acetamide (contains an amine), followed by acetates (contains an ester). Their most notable reactions tend to form more acyl compounds.
Carboxylic acids are named in [alk]oic acid. They don't really have a prefix because they have the highest priority of all functional groups.
When working with carboxylic acids, it's also worth being able to identify lactones, which are cyclic compounds with two oxygens, one branching off in a double bonds and one within the ring itself. Hydrolysis of these breaks the chain around the oxygen to make a carboxylic acid. The other end will be a lone alcohol.
When it comes to nucleophilic substitution, aldehydes are more reactive than ketones because of sterics - the aldehyde only needs to deal with a small hydrogen atom on one end, after all. Ketones have an R group on both sides of the carbon to get in the way. The former are named in [alk]al or oxo[alk] format depending on priority, and chains are numbered so that the aldehyde carbon is in the 1 position. The latter follow [alk]one or keto[alk] format.
This isn't their real name, I'm just calling them that. These are patterns or notable reactions worth memorizing because they come up multiple times.
TKTK: E1, SN1, nucleophiles, all that
Hydrolysis occurs when a water molecule breaks chemical bonds by being a nucleophile.
TKTK
There's also a bunch of reactions named after specific people because Latin would be just too convenient and easy.
TKTK
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