GENERAL CHEMISTRY explained in 19 minutes

Summary

Le script explore les bases de la chimie, des atomes aux réactions. Il explique la structure atomique, l'importance des électrons de valence et la table périodique. Il décrit les liaisons covalentes, ioniques et métalliques, ainsi que les forces intermoléculaires. Le script aborde également les états de la matière, les changements physiques et chimiques, et les équilibres chimiques. Il mentionne les réactions de combustion, la stoechiometrie, l'enthalpie, le pH et les réactions de réduction-oxydation. Enfin, il introduit les nombres quantiques et la configuration électronique des atomes.

Takeaways

• 🌌 Tout est fait d'atomes, y compris vous.
• 🏠 Les atomes se composent d'un noyau et d'électrons, le noyau étant fait de protons et de neutrons.
• 🌊 L'eau est faite d'hydrogène et d'oxygène, tandis que le sodium est un élément différent.
• ⚛️ La mécanique quantique nous dit que l'apparence réelle des atomes est plus complexe que ce que nous imaginons.
• 📊 La table des éléments est une liste de tous les éléments, classés par leur nombre d'électrons de valence.
• 🔋 Les éléments d'un même groupe ont le même nombre d'électrons de valence, qui correspond au numéro de groupe.
• 🧲 Les éléments avec le même nombre d'électrons de valence ont tendance à montrer un comportement similaire dans les réactions chimiques.
• 🚀 Les éléments d'une même période ont le même nombre de couches électroniques, qui augmente du haut vers le bas.
• ⚖️ Les isotopes sont des formes d'un élément avec un nombre différent de neutrons, la plupart étant instables.
• 🔥 Les atomes avec autant d'électrons que de protons sont neutres, sinon ils sont des ions avec une charge positive ou négative.
• 🔑 La table des éléments est divisée en métaux, non-métaux et semi-métaux, et décrit les propriétés des éléments.
• 🤝 Deux ou plusieurs atomes liés forment une molécule, et s'ils sont de différents éléments, ils forment un composé.
• 🏗️ Les liaisons covalentes, ioniques et métalliques sont des façons différentes dont les atomes peuvent se lier entre eux.
• 🌡️ La température est l'énergie cinétique moyenne des particules, et l'entropie mesure le niveau de désordre.
• 🔥 Les réactions chimiques libèrent de l'énergie et ont lieu pour atteindre un état plus stable.
• 🧪 La stoechiometrie décrit les rapports dans lesquels les réactifs se combinent, basés sur la conservation de la matière.
• ⚡️ Les réactions chimiques ont besoin d'une énergie d'activation pour avoir lieu, et les catalyseurs peuvent la réduire.
• 🌡️ L'enthalpie est la mesure de l'énergie interne ou du contenu calorifique d'un système, et les réactions exothermiques libèrent de la chaleur.
• ⚖️ L'équilibre chimique se produit lorsque des réactions reversibles ont lieu à la même vitesse dans les deux directions.
• 🔄 Les réactions de réduction-oxydation (redox) changent le nombre d'oxydation des éléments et impliquent un transfert d'électrons.
• ⚛️ Les électrons dans un atome sont décrits par quatre nombres quantiques qui déterminent leur position et leur état.

Q & A

Qu'est-ce qu'un atome et de quoi est-il composé?

Un atome est constitué d'un noyau de protons et de neutrons, entouré par des électrons.

Comment les éléments sont-ils déterminés?

Les éléments sont déterminés par le nombre de protons dans leur noyau.

Qu'est-ce qu'un électron de valence et pourquoi est-il important?

Les électrons de valence sont les électrons situés dans la couche externe d'un atome. Ils sont importants car ils déterminent la réactivité chimique de l'atome.

Qu'est-ce qu'un ion et comment se forme-t-il?

Un ion est un atome ou une molécule ayant une charge électrique due à la perte ou au gain d'un ou plusieurs électrons. Un ion négatif est appelé anion et un ion positif est appelé cation.

Quels sont les types de liaisons chimiques et comment se forment-ils?

Il existe des liaisons ioniques, covalentes, métalliques, et hydrogène. Les liaisons ioniques se forment par le transfert d'électrons, les liaisons covalentes par le partage d'électrons, les liaisons métalliques par des électrons délocalisés, et les liaisons hydrogène par des interactions entre dipôles.

Qu'est-ce qu'une molécule et un composé?

Une molécule est un ensemble de deux atomes ou plus liés ensemble. Un composé est une molécule composée d'au moins deux éléments différents.

Comment le tableau périodique est-il organisé?

Le tableau périodique est organisé par le nombre croissant de protons, en colonnes appelées groupes et en lignes appelées périodes. Les éléments d'un même groupe ont le même nombre d'électrons de valence.

Qu'est-ce qu'un isotope?

Un isotope est une variante d'un élément ayant le même nombre de protons mais un nombre différent de neutrons.

Qu'est-ce qu'une liaison covalente polaire et non polaire?

Une liaison covalente non polaire partage les électrons de manière égale entre deux atomes, tandis qu'une liaison covalente polaire partage les électrons de manière inégale, créant des charges partielles.

Qu'est-ce qu'une réaction redox?

Une réaction redox (réduction-oxydation) implique le transfert d'électrons entre deux substances, où une substance est oxydée (perd des électrons) et l'autre est réduite (gagne des électrons).

Outlines

00:00

🌌 Introduction à la chimie et à l'atome

Le premier paragraphe introduit les bases de la chimie en expliquant que tout est fait d'atomes, y compris les êtres humains. Il décrit la structure de l'atome avec un noyau composé de protons et de neutrons, et des électrons qui orbitent autour. L'importance du nombre de protons pour identifier les éléments est soulignée, ainsi que la formation d'eau à partir d'hydrogène et d'oxygène. Le paragraphe mentionne également l'existence de différents groupes d'éléments dans la table périodique, qui partagent un certain nombre d'électrons de valence, et comment ces éléments ont tendance à montrer des comportements chimiques similaires. La charge des atomes et la formation d'ions sont également abordées.

05:04

🔬 Les liaisons chimiques et les interactions

Le deuxième paragraphe explore les différents types de liaisons chimiques telles que les liaisons covalentes, ioniques et métalliques. Il explique comment les atomes cherchent à atteindre un état d'énergie la plus basse en remplissant leur coquille extérieure d'électrons, ce qui conduit à la formation de liaisons covalentes. La polarité des liaisons est également examinée, en utilisant l'eau comme exemple pour montrer comment la différence d'électronégativité peut entraîner une charge partielle et un dipole électrique. Les forces intermoléculaires, y compris les liaisons hydrogène et les forces de Van der Waals, sont décrites, ainsi que leur rôle dans la solubilité et la structure des matières.

10:08

🧪 Les états de la matière et les réactions chimiques

Le troisième paragraphe traite des trois états de la matière - solide, liquide et gaz - et comment la température et la pression affectent ces états. Il explique le concept de température comme l'énergie cinétique moyenne des particules et d'entropie comme la mesure du désordre. La relation entre les liaisons fortes et les points de fusion élevés, ainsi que la formation de plasma à haute température ou potentiel électrique, est abordée. Le paragraphe décrit également les types de réactions chimiques, la stœchiométrie, et l'importance de la conservation de la masse. La différence entre les changements physiques et chimiques est expliquée, ainsi que le rôle de l'énergie d'activation et des catalyseurs dans les réactions.

15:11

⚗️ La chimie avancée et les équilibres

Le quatrième paragraphe approfondit la discussion sur les réactions chimiques en abordant l'enthalpie, les réactions exothermiques et endothermiques, et l'énergie libre de Gibbs. Il explique comment les réactions spontanées et les équilibres chimiques sont influencés par l'entropie et la température. La définition des acides et des bases selon Brondsted-Lowry, les acides amphotères, et la mesure de la force d'un acide via le pH sont également discutées. Le paragraphe se termine avec une explication des réactions de réduction-oxydation (redox), où les changements dans les nombres d'oxydation des éléments sont examinés, ainsi que la description des nombres quantiques et de la configuration électronique des atomes.

Keywords

💡Atome

Un atome est la plus petite partie d'un élément chimique qui peut exister sans être séparée en parties moins complexes. Il est composé d'un noyau dense contenant des protons et des neutrons, entouré d'électrons. Dans le thème de la vidéo, l'atome est la base de la matière et de la chimie, et la compréhension de sa structure est cruciale pour comprendre les réactions chimiques et les propriétés des éléments.

💡Noyau atomique

Le noyau atomique est le centre d'un atome, composé de protons, qui sont des particules positives, et de neutrons, qui sont neutres. Le nombre de protons détermine le type d'élément. Dans le contexte de la vidéo, le noyau est essentiel pour comprendre la nature des éléments et comment ils interagissent lors des réactions chimiques.

💡Électrons

Les électrons sont des particules négatives qui orbitent autour du noyau atomique. Ils sont répartis dans des couches ou 'shells' et les électrons de la couche extérieure sont appelés 'électrons de valence'. La vidéo explique que la plupart de la chimie est liée au comportement de ces électrons de valence, qui influencent les réactions chimiques des éléments.

💡Tableau périodique

Le tableau périodique est un outil qui classe les éléments en fonction de leurs nombres atomiques et de leurs propriétés chimiques. Chaque élément y est représenté par son symbole et son numéro de protons, qui correspond également au nombre d'électrons dans l'atome. La vidéo souligne l'importance du tableau périodique pour comprendre les similitudes et les différences dans le comportement chimique des éléments.

💡Ions

Les ions sont des atomes qui ont un nombre net de charges, soit因为他们获得了额外的电子（anions, 负离子）, soit因为他们 en ont perdu (cations, 正离子). La charge des ions est déterminée par l'écart entre le nombre d'électrons et de protons. Dans le script, les ions jouent un rôle clé dans la formation de liaisons chimiques et dans les réactions telles que les liaisons covalentes et ioniques.

💡Liaisons covalentes

Les liaisons covalentes sont des liaisons chimiques formées par le partage électronique entre deux atomes. Cette forme de liaison est souvent observée lorsque deux atomes n'ayant pas de couche extérieure complète peuvent en obtenir une en partageant des électrons. La vidéo mentionne que les liaisons covalentes sont causées par l'attraction du noyau atomique sur les électrons d'un autre atome, ce qui est mesuré par l'électronégativité.

💡Électronégativité

L'électronégativité est une mesure de la tendance d'un atome à attirer des électrons dans une liaison chimique. Plus un élément a une forte électronégativité, plus il attire fortement les électrons. La vidéo indique que l'électronégativité augmente en remontant et en traversant le tableau périodique, ce qui influence le type de liaison chimique formée, comme les liaisons covalentes ou ioniques.

💡Liaisons ioniques

Les liaisons ioniques sont créées lorsqu'un atome donne un ou plusieurs électrons à un autre atome, formant ainsi des ions. Dans le script, la formation d'une liaison ionic est illustrée par l'exemple de la chlorure de sodium, où le sodium (qui a un électron de trop) le cède à l'chlore (qui en a besoin), créant ainsi un ion cationique et un anion.

💡Liaisons métalliques

Les liaisons métalliques sont des liaisons chimiques spéciales qui se produisent dans les métaux. Elles impliquent un réseau de noyaux positifs entourés d'électrons qui se déplacent librement. Cette structure permet aux métaux de conduire l'électricité et la chaleur, ainsi que d'être malléables. La vidéo explique que les électrons de valence dans une liaison métallique sont 'délocalisés', ce qui signifie qu'ils ne sont loyals qu'à un seul noyau.

💡Forces intermoléculaires

Les forces intermoléculaires, ou IMFs, sont les attractions qui agissent entre les molécules. Elles incluent les liaisons hydrogène et les forces de Van der Waals. La vidéo explique que ces forces sont importantes pour la solubilité des substances dans l'eau et la manière dont les molécules se répartissent en fonction de leurs charges.

💡Isomères

Les isomères sont des molécules qui ont la même formule moléculaire mais des structures spatiales différentes. La vidéo mentionne les isomères pour illustrer comment deux molécules ayant la même formule peuvent avoir des propriétés très différentes, comme le montre l'exemple de la graphite et du diamant, qui sont tous les deux de simples formes de carbone.

💡Quantum Numbers

Les nombres quantiques sont des entiers ou des valeurs discrètes qui décrivent les états énergétiques d'un électron dans un atome. Le script explique qu'il y a quatre nombres quantiques (N, l, ml, et ms) qui déterminent les 'shells', les 'subshells', et les 'orbitaux' où les électrons peuvent être trouvés. Ces nombres sont essentiels pour comprendre la configuration électronique des atomes et comment les électrons sont distribués dans l'espace autour du noyau.

💡Principe d'Aufbau

Le principe d'Aufbau est une règle utilisée pour déterminer l'ordre dans lequel les sous-coquilles et les orbitaux sont remplis par les électrons dans un atome. La vidéo utilise ce principe pour expliquer comment les configurations électroniques des éléments sont déterminées en suivant un ordre précis, ce qui aide à comprendre les électrons de valence et les propriétés chimiques des éléments.

Highlights

Everything is made of atoms. Atoms consist of a core and some electrons.

Depending on the number of protons, you get different elements.

Water is made of Hydrogen and Oxygen.

Quantum mechanics tells us that this is not what atoms actually look like.

The electrons in the outermost shell are called 'valence electrons'. Most of chemistry is really just the behavior of these electrons.

Elements in the same column or 'group' have the same number of valence electrons.

For the main groups, the number of valence electrons is just the group number from 1 to 8.

Elements with the same number of valence electrons tend to show similar behavior in chemical reactions.

All elements in the same row or 'period' have the same number of shells.

Depending on the number of neutrons in the core, you get different isotopes of the same element.

Charged atoms are called 'ions'. Negative ions are 'anions', and positive ions are 'cations'.

The periodic table tells you the name, symbol, number of protons, total number of electrons, and the atomic mass of an element.

Two or more atoms bonded together form a molecule. If you have at least two different elements, you get a 'compound'.

Compounds often behave completely differently than the elements they’re made of.

There are many ways to write molecules, such as the Molecular formula.

Transcripts

Everything is made of atoms. Yes, even you. Atoms consist of a core and some electrons.

The core is made of protons and neutrons. And depending on the number of protons, you

get different elements. Water is made of Hydrogen and Oxygen. This

is some Sodium. Hm, I wonder what happens when you mix them…oh, whoopsie.

Quantum mechanics tells us that this is not what atoms actually look like, they look more

like this, but we’ll get to that later. For now, just think of atoms as having multiple

electron “shells”. The electrons in the outermost shell are called “valence electrons”.

Most of chemistry is really just the behaviour of these electrons.

Every element is listed in the periodic table. All elements in the same column or “group”

have the same number of valence electrons. For the main groups, the number of valence

electrons is just the group number from 1 to 8. Except for helium. It’s too small

to have 8 electrons, it can only have 2. But still, it acts like a noble gas, so it’s

kind of just grouped in with those. Luckily, the transition metals also follow a nice pattern!

That was a lie, it’s kind of a mess. But that’s not so important for now, so we’ll

get to that later. Elements with the same number of valence electrons

tend to show similar behaviour in chemical reactions. For example, the first group, without

hydrogen, is called the “alkali metals”. Here’s some things they have in common:

They have one valence electron. They’re shiny metals. They’re kind of soft. And

they do this sometimes. All elements in the same row or “period”

have the same number of shells. This number increases from top to bottom. Also, the mass

gets bigger from left to right, as each element gains a proton, an electron and some neutrons.

Depending on the number of neutrons in the core, you get different isotopes of the same

element, most of which are pretty unstable, and fall apart, releasing ionizing radiation.

Fun fact! That stuff will kill you. If an atom has the same amount of electrons

as protons, it has no charge. If it has more, it has a negative charge, and if it has less,

it has a positive charge. Charged atoms are called “ions”, negative ions are “anions”

and positive ions are “cations”. The periodic table is also pretty much a dictionary,

as every cell tells you: The name and symbol of an element, the number

of protons in the core, which is also the total number of electrons and the atomic mass,

which is the mass of neutrons and protons combined.

The periodic table is roughly divided into three categories: Left of this line are the

metals. Right of it are the non-metals, which are mostly gases, and the line is called the

“semimetals”, which have properties that fall somewhere inbetween.

Two or more atoms bonded together form a molecule. If you have at least two different elements,

you get a “compound”. Oh yeah, this is probably a good time to mention that compounds

often behave completely differently than the elements they’re made of. Like, put together

an explosive metal and a toxic gas, and you get, of course, an even more explo- table

salt. You get tablesalt. There’s many ways to write molecules, for

example the Molecular formula, where you just count the number of each atom in a molecule,

and write them as a subscript number next to the element symbol.

But that has some problems. Look at these two molecules: They have the same molecular

formula, but obviously, they’re not the same. They’re isomers.

Showing this difference is probably kind of important: It’s the only thing that separates

graphite from diamonds, because they’re both just fancy versions of carbon, and I

don’t think anyone’s going to go “mmm, yes, this dusty black blob is indeed very

expensive”. One way to show the structure of an atom is

a Lewis-Dot-Structure, which represents the valence electrons and bonds as dots and lines.

That is also going to help us understand why atoms bond in the first place.

You see, everything in the universe wants to get to a state of lower energy. That’s

why a ball on a hill will roll down by itself, because that decreases its potential energy.

This trend also applies to atoms: The state of lowest potential energy is having a full

outer shell of electrons, which is most often eight, or in the case of hydrogen and helium,

two. If you think back to the periodic table, you’ll see that all noble gases already

have a full outer shell, which is why they don’t really want to react with anything.

If two atoms don’t have a full outer shell, but can achieve one by sharing electrons,

they will naturally do so, the same way a ball will go downhill, as their combined energy

would be lower than if they were separate. The sharing of electrons is called a “covalent

bond”. These bonds are also caused by the positively charged nucleus of an atom tugging

on electrons of another atom. The strength of this pull is called “electronegativity”.

In the periodic table, the electronegativity increases from bottom left to the top right.

Therefore, Fluorine has the strongest pull. It’s just, unbelievably desperate for an

electron. If the difference in electronegativity is

bigger than about 1.7, you get an ionic bond. A good example is Sodium Chloride. Chlorine

would do anything for an electron, while Sodium has one too many and just kind of wants to

get rid of it anyway. “Perfect!” they both say, forming an ionic bond, where sodium

loses an electron and turns into a cation, and chlorine gains an electron and turns into

an anion. That seems pretty important…you might wanna remember it.

The most common place you see Ionic bonds is in salt, yes, also table salt, but more

generally, when metals and nonmetals bond, you get “a” salt, which is just a grid

of ions. Speaking of metals, a pure metal forms “metallic

bonds”. You can imagine this as a huge grid of the positively charged nuclei, which are

surrounded by freely moving electrons. You see, in a metal grid, the valence electrons

are kind of promiscuous, or as nerds call it, “delocalized”. They can move freely

in a giant playground of nuclei, instead of being loyal to just one.

This kind of bond is responsible for the properties of metals, like conducting electricity and

heat, and also, being malleable, as in being kind of bendy. Like, you can hammer on this

stuff until it’s the most deformed, unelegant and ugly looking piece of material ever known,

and it will just limp along as if nothing ever happened.

If the difference in electronegativity is lower than about 0.5, the electrons are shared

pretty equally and you get a nonpolar covalent bond. If it’s bigger than 0.5 but smaller

than around 1.7, one of the elements is pulling on the electrons pretty hard. Not quite hard

enough to completely steal an electron, but definitely hard enough to skew the electrons

a bit, making it a polar covalent bond. An example is water. Oxygen has a very high

electronegativity compared to hydrogen. As a result, it pulls the electrons of hydrogen

so hard, that they kind of belong to oxygen, giving it a partial negative charge, and leaving

hydrogen with a partial positive charge. The presence of two poles with opposite charge

is called a “electric dipole”. All permanent dipole molecules can interact

with each other, and really, with anything that has a charge. As a result, the molecules

will tug on each other and arrange themselves in a way that oppositely charged ends are

next to each other. The forces acting between them are called “intermolecular forces”

or IMFs. A specific example is hydrogen bonds, where

hydrogen bonds to something very electronegative, like Fluorine, Oxygen or Nitrogen, creating

strong dipoles that tug on each other. The polarity of water also explains why it’s

one of the most versatile solvents to exist. It can pull apart molecules by tugging on

charges, and it keeps them apart by surrounding a particle with its oppositely charged end.

This way, it can dissolve almost anything with an uneven distribution of charges.

Water cannot dissolve nonpolar molecules though. It’s the reason why water and oil don’t

mix, since fat molecules are nonpolar, while water is polar.

Just remember the ancient saying: “Similia Similibus Solventur”, or in a language that’s

actually spoken: similar things will dissolve similar things.

But even if molecules are not polar at all, there can be electrostatic forces acting between

them. How? Electrons move around inside atoms, and by pure chance they can end up on one

side of the atom, creating a momentary dipole, which influences other particles next to it

to become a dipole as well. At least for a very short time, as the electrons keep moving

and the dipole disappears. This is called “Van der Waals forces”.

Fun fact! Soap works because the molecules that it’s made from, which are called “surfactants”

have a polar “head”, and a nonpolar “tail”. This way, when in water, they can surround

for example nonpolar fat molecules and form “micelles”, which, along with the water,

transport the dirt particles away. These are the most important bonds and forces

ranked by strength: [Ionic Bonds, Covalent Bonds, Metallic Bonds, Hydrogen Bonds, Van

der Waals Forces]

There are three main states of matter: Solid, liquid and gas.

Solids are tightly packed in a fixed structures, where the particles can only wiggle. Unless,

you know, you smash them. In liquids, the particles can move freely but are still confined

to a fixed volume, as the forces between them are still strong enough to keep them together,

and the particles in gases have enough energy to just do whatever they want and fill up

all the volume you give them. Knowing this we can define two important words:

Temperature is the average kinetic energy of particles in a system, or how much and

how fast they move and entropy is the amount of disorder.

Substances tend to be solid at low temperature and/or high pressure, which is a state of

low entropy, as they’re neatly organized and don’t move that much, and gas at high

temperature and/or low pressure, where they move around like crazy, so it’s a state

of high entropy. Strong bonds, like ionic bonds, lead to high

melting points, as they take a lot of energy and therefore a high temperature to break

apart. That’s why most salts are solid at room temperature, whereas water, which is

only being held together by hydrogen bonds, is a liquid.

Well, actually (!), there’s another state called “plasma” which is ionized gas and

can exist at very high temperatures, such as in stars, or very high electric potential.

The latter is used for neon lights. Gas is ionized in a tube with a very high voltage.

Collosions of the ions with other particles makes their electrons move to a higher energy

state. Once they falls back down, the difference in energy is released as light.

The colour of the light depends on the element that’s used in the tube, as each element

has different, but fixed energy levels, and the difference between those determines the

energy and therefore the frequency of the released light, which is what changes the

colour. All possible frequencies, that an element can emit, are called the “emission

spectrum”. All matter can be divided into two categories:

Pure substances, which can consist of one element or one compound, and mixtures.

Mixtures consist of at least two pure substances and can be homogeneous or heterogeneous. Homogeneous

means the substances will mix evenly and the mixture looks the same everywhere, like salt

in water, which is a “solution”. Heterogeneous mixtures look different depending

on where you look. They have distinct regions made of separate substances. One example is

sand in water, which is called a “suspension”. Okay, well what about milk? That looks the

same everywhere, so it must be homogeneous! Uhhh, no. Milk is something we call a “colloid”,

or more precisely an “emulsion”. The difference between salt water and milk is that the solute

doesn’t fully dissolve in the solvent, meaning there are bigger particles than in a solution,

but smaller particles than in a suspension. This allows the particles to stay evenly distributed,

but not fully dissolved, placing them somewhere between solutions and suspensions.

 

Hey remember sodium and water? What’s going on here? Explosions are really just chemical

reactions that release a lot of energy in a very short amount of time. Also, they expand,

like, a lot. There’s a couple types of chemical reactions:

synthesis, decomposition, single replacement, and double replacement. Here’s an example

for each one. They all happen mainly for one reason: To

decrease energy and get to a more stable state. Chemical reactions happen in certain ratios,

for example, to produce water molecules, you need twice the amount of hydrogen compared

to oxygen. This is called “Stoichiometry”. These ratios are based on the conservation

of mass, which says that mass cannot be created or destroyed, only converted. Practically,

when dealing with reaction equations, you have to make sure that there’s the same

amount of atoms on each side of the equation, and if not, balance it out element by element.

As a rule of thumb, you should balance out the metals first, then the nonmetals, and

hydrogen and oxygen at the end. But, it’s really just trial and error until everything

is balanced. Okay, but if we wanted to make this reaction

happen in a lab, how would we know that we have exactly twice the amount of hydrogen

compared to oxygen? You can’t just take 20 grams of this and mix it with 10 grams

of that, because the atoms don’t weigh the same, so 10 grams of both contain a different

amount of particles. What to do?

Just look up the atomic mass of the reactants and take that amount in grams. You’ll get

exactly this amount of particles. That is 1 mole, which is just an amount of something,

kind of like “a dozen”. In other words, we can interpret the reaction as 2 moles of

this react with 1 mole of that, which we can easily measure.

It’s important to differentiate between physical and chemical changes, as reactions

only take place in the latter. Physical change happens when the appearance changes but the

substance does not, for example hammering metal. A chemical change happens when the

substances themselves change and this is often accompanied by bubbles, a funky smell, or,

you guessed it, explosions. All chemical reactions need activation energy

to take place. Wood won’t just spontaneously react with oxygen and start burning, or else,

you know, the planet would be on fire, but if you give it enough energy, it will. Catalysts

reduce the activation energy needed for a reaction, which makes it happen easier and

faster. And as a neat bonus, they don’t even get used up during the reaction, so you

can just reuse them! Because chemical reactions are changes in

energy, it’s quite useful to keep track of it.

“Enthalpy” is, simply put, the internal energy or heat content of a system. If the

total enthalpy of a reaction is lower at the end than at the beginning, heat was given

off to the surroundings, which is an “exothermic” reaction. If it’s the other way around a

reaction is “endothermic”. It’s easy to see how exothermic reactions

can be spontaneous. It’s kind of like a ball on a hill. It will only start rolling

if you push it a little bit, but then it will keep rolling on its own, just like wood keeps

burning on its own. But in endothermic reactions, you have to keep putting in energy, like pushing

a ball uphill. That doesn’t just spontaneously happen, right? Well, yes, actually, it does.

To get the whole picture, we have to look at Gibbs Free Energy, which looks at the change

of enthalpy but also entropy of a system which is dependent on temperature.

If this whole thing is less than zero, the reaction is “exergonic”, or spontaneous,

because free energy was released. If it’s bigger than zero, it’s “endergonic”,

or not spontaneous, because free energy was needed and absorbed.

Here’s where temperature and entropy come into play: Even if delta H is positive, so

the reaction is endothermic, if the change in entropy is big enough, it can offset this

and make the total free energy negative, which means a reaction is spontaneous. But this

is strongly dependent on the temperature. For example, melting an ice cube is endothermic,

because it absorbs heat, but also, it increases the entropy a lot, as the neatly organized

ice turns to water, which is just kind of a mess. This can happen spontaneously, but

only if the temperature is above 0. If it’s below 0, the water will spontaneously freeze,

which is exothermic. If it’s exactly 0, then no reaction will

take place spontaneously. In other words, if delta G is 0, we’re at equilibrium.

Chemical equilibriums exist when reversible reactions take place at the same speed in

both directions, which means that even if reactions are taking place, the concentrations

of both sides stay the same, and to someone watching from the outside, nothing seems to

be happening. We often find chemical equilibriums in phase

changes, but also acid base chemistry. According to Brondsted-Lowry, an acid is a

molecule that donates protons, while bases accept protons. A proton in this case is just

a hydrogen ion. So, with this definition, a molecule with

at least one hydrogen that it can throw away can be an acid, and anything that can pick

it up can be a base. This also means that once they react, they turn into the conjugate

opposite, as an acid that gave away a proton can now accept one back, which is what bases

do. A molecule that can act as both an acid and

a base is called "amphoteric".

A strong acid will dissociate almost completely into its ionic form, giving off a lot of protons

to the water and therefore creating lots of hydronium ions. A weak acid just won’t dissociate

nearly as much, giving us a lower concentration of hydronium ions.

So, to measure the strength of an acid we can measure the concentration of Hydronium

ions. This is called the “pH”. Mathematically, it’s defined as the negative

log of the hydronium concentration, which means one step on the scale is a 10x change,

and also, since it’s a negative log, the higher the concentration, the lower the pH.

For example. Pure water is in a chemical equilibrium. There’s exactly one hydronium ion for every

10 million water molecules. In other words, the concentration of hydronium is 1 over 10

million, or 1 times 10^-7. Taking the negative log of this gives us a pH of 7, which is considered

neutral. Anything lower than 7 is acidic, and anything

above is “basic”, unlike you. You can do the same thing with hydroxide ions

and you will get the pOH, which keep track of basicity. Fun Fact! The pH and pOH always

add up to 14, because they counteract each other, so by knowing one, you know both! Now,

if you have a strong base and a strong acid and you pour them together, no, they will

not explode, they will neutralize by forming water along with a salt, which is neutral.

For example, Hydrochloride and Sodium Hydroxide will form water and table salt.

Oh yeah, speaking of table salt, remember how it consists of ionic bonds, because sodium

transfers an electron to chlorine? Well that is called a Reduction-Oxidation reaction or

“redox”. If sodium chloride forms out of it’s pure

elements, the sodium gets oxidized as it loses an electron, and the chlorine gets reduced,

as it gains an electron. Logically, Sodium is the oxidant, and chlorine is the reductant.

Of course not, that would make sense, it’s other way around.

More accurately, redox reactions are reactions that change the oxidation numbers of elements,

which are kind of like imaginary charges. There’s just a few rules you have to know

to figure those out: Hydrogen is mostly +1, Oxygen is mostly -2,

halogens are mostly -1, single elements are always 0, and the numbers of all atoms in

a molecule always have to add up to the molecule’s charge. So this would total 0, while single

ions just have their charge as the oxidation number. For example, in sulfuric acid, we

have 4 oxygens, which totals -8, we have two hydrogens, which brings the total to -6, and

since the whole molecule is neutral, sulfur must have an oxidation number of +6.

Just by looking at the oxidation numbers of reactants and products you can deduce the

flow of electrons, which gives you these equations. If redox reactions happen in acidic or basic

solutions, you can balance out the charges with the ions, and fix the stoichiometry with

water.  

Okay, now to this weird looking thing. I spared you from it because for describing electrons,

this is very simple, and this not. But, this is actually like, pretty wrong, electrons

don’t orbit in circles. Here’s how it actually works:

All electrons inside an atom are described by four quantum numbers. N, l, ml, and ms.

N corresponds to the shells, so all electrons with the same n are in the same shell.

Within the shells we have subshells, with multiple orbitals, which are three dimensional

regions in space where electrons could be. We know these exist thanks to schrödinger’s

equation, which gives a probabilistic wave function. You can imagine it as cloud, and

the denser it is, the more likely an electron is to be there if we were to look for it.

L describes the shape and ml the orientation of orbitals in a subshell.

There are four subshells called s, p, d and f. If electrons have the same l, they’re

in the same subshell. If electrons have the same n, l, and ml, they are in the same orbital.

Also, the number of orbitals increases by two for every bigger subshell, starting at

just one for s. The last quantum number describes an intrinsic

property of electrons called “spin”, which can have two values.

Some guy named Pauli said two electrons can never have the exact same quantum numbers

inside one atom. Since ms can only have two values, every orbital defined by n l and ml,

can hold a maximum of 2 electrons with opposite spin.

Therefore the s subshell can hold 2 electrons, the p subshell can hold 6, d can hold 10,

and f can hold 14. Now, the quantum numbers restrain each other

like this, which means that the first shell can only have an s subshell, the second can

have an s and a p subshell, and so on. This means that the first shell can hold a

total of 2 electrons, the second can hold 8, the third can hold 18, and generally, the

number of electrons a shell can hold follows the rule 2n2, with n being the principal quantum

number. The principal quantum number, and therefore total number of shells increases

from top to bottom in the periodic table, from 1 to 7.

Every element has a different number of electrons that fill up these orbitals, and the different

subshells and orbitals are filled in a specific order, called the “Aufbauprinciple”: just

write down the subshells like this and draw diagonal lines from top right to bottom left.

To get an electron configuration, just look up the number of electrons of the element

in the periodic table, and fill up the subshells in this order, until there are no electrons

left. This would be the electron configuration of Sodium.

You can also look up the next smallest noble gas and shorten it by just referring to its

electron configuration as the base, because those shells are full, and don’t change

for any bigger elements. This is also how you can figure out the valence electrons for

transition metals. Just look up their electron configuration, ignore the full shells of the

next smallest noble gas, and the remaining electrons are the valence electrons! Easy

peasy. Anyways! All this knowledge going to cost

you one subscribe and a thumbs up, thank you very much, your comment is my delight, and

I shall now guide you, fine person, to the exit, where the next lesson is excitedly waiting

for you.