Models are great but I don't mean that kind of model, I find this culture very strange. I'm talking about patterns that make you try things that you wouldn't otherwise try. It may be something too big to see, like our solar system, Or just as small as a cell or something that doesn't exist like the Millennium Falcon spacecraft. Or something that might be dangerous to put in the office like a catapult. Sometimes it is difficult and perhaps impossible to fully understand things without modeling them. But the models don't have to be 3D. The scientific definition of a form is anything that represents something else. Whether physical or imaginary, As is the musical note on a sample sheet for a piece of music. The same applies to chemistry. Chemists use many models or simplified versions of reality to help them understand atoms and their interactions. Because the universe is strange. This ball-and-stick model is a visualization of a molecule having spherical atoms Connected with clearly defined links. This model of molecules is a great way to start understanding chemical bonds. But I have to move to a higher level of beginner level To understand some of the models that interpret links in a more pleasant complexity.
Technical details require more intricate and glamorous models. So, although this episode of our show is not going to talk about Brazilian women in swimwear However, I promise you that your hope will not disappoint. It turns out that the chemical bonds aren't like little sticks at all. Bonded atoms, or molecules, are groups of atoms that are conjugated Close together because that is what keeps her energy to a minimum. So if you throw these patterns of atoms into the air and let them scatter away from each other So that's fun and cool to me, but those little balls will have more energy And it's not the ideal situation for an atom, is it? In fact, the only thing that binds two atoms together by a chemical bond is a group of electrons, And it does not sit still between the atoms and sticks everything together.
Rather, it is in constant motion near the nucleus in a somewhat predictable pattern. In a covalent bond, the bonding electrons spend most of their time between the nuclei, The nuclei stay close together because they are attracted to electrons. Frankly, the idea that electrons bind everything together is in itself another paradigm. Idea that represents particles in a visual way. It is a more accurate representation of reality than the ball and stick model.
But the ball-and-stick model is not useless, It helps us visualize and understand many important things about molecules And it's also nice looking. Imagine if instead of generalizing about how chemicals behave, like water dissolves salt, We had to memorize by heart every behavior for every substance. Nobody would have accomplished anything else in his life. Yes, to give our minds room to do more important and better things. So you can be sure that some of the models are really cool even though they're so simplified that they're outright lies. Rather, it is important to realize that all models are flawed to some degree. Think about the models people are comparing themselves to. You think the women are in lingerie catalogs and the men are in the black and white perfume ads They look in that form on a Saturday morning after a long night of doing what the performers do on a Friday night? In fact, if the scientific model were an ideal embodiment of reality, it would no longer be anthropomorphic but rather a reality.
So, in addition to understanding how a model represents reality, We must also know the ways in which reality is not representative So as not to build on it a set of wrong assumptions. Unfortunately, sometimes the models are not only too simplistic but wrong. The chemical bond model is no exception: over the centuries, it has been updated The more the results of the experiments provide us with information about how the universe works. Ancient scientists, including Isaac Newton, thought that atoms were bound together because they were sticky. Or because it has small hooks like Velcro that hold it together. That was their link model. In the nineteenth century, chemists such as Breselius discovered positive and negative charges Accompanying chemicals in certain situations He and his contemporaries theorized that these charges are the force that binds particles together. This model was better than its predecessor, but still quite imprecise Because they thought that atoms were attracted to each other like magnets.
After the discovery of electrons in the 1980s, chemists were able to understand The true nature of chemical bonds. And in 1916, the American chemist Gilbert Newton Lewis described the covalent bond As two atoms sharing electrons. And modern chemists still use this model as a simple method To represent chemical bonds on paper. The Lewis structure is a two-dimensional model that represents covalent bonds in the form of straight lines.
Unbound valence electrons that are at the highest energy level of an atom are in the form of points. The inner electrons are not represented at all, although the model was developed to explain covalent bonds However, it also applies to ionic bonds. In Lewis structure, bonds are formed by pairs of valence electrons called bond pairs In the space between two atoms, The pairs of electrons attached to one atom are known as monopairs. As you can recall, atoms are most stable when most of the valence shells are full. For many atoms this requires 8 electrons, so this is called the octet rule. If you are preparing to hear some exceptions to this rule, then you are correct. A hydrogen atom can only bond with two electrons, not 8. And this will be more understandable when you see our next episode of atomic orbitals. But there are also elements on and below the third line of the periodic table It often has more than 8 valence electrons. Beryllium boron are known to have strange numbers like 6 or 12 electrons. Therefore, the rule of octets is an observation rather than a rule.
Let's stay on lines 1 and 2 of the table to keep it simple. Suppose I want to plot the Lewis composition for sodium chloride, Sodium has one valence electron and chlorine has 7, since sodium is a metal This means that the bond will be ionic, meaning that electrons are transferred. Sodium transfers the valence electron to chlorine producing a positive charge for sodium and a negative charge for chlorine. The two ions are attracted to each other because of their opposite charges. And they write a little separate because they don't share the electrons. But they're not far apart because the ions stay close enough to neutralize their charges. Lewis fitting uses a line to denote covalent bonds But we're not going to do this here because there are no covalent bonds, It is an ionic bond and there is no connection between ions.
So, this is what salt looks like from a Lewis syntactic point of view. Covalent bonds are more complex. It is better if you follow some specific steps. Let's try this with water. First, find out the total number of valence electrons available. It doesn't matter which atom it came from or how it was arranged before it started. Each hydrogen atom has one valence electron, and oxygen has 6 valence electrons, meaning that the total is 8 electrons. Hydrogen or oxygen do not have enough valence electrons to be stable. So they share the electrons to make up for the deficiency, Just as sharing a meal can lead to the formation of a new friendship, so sharing a meal causes a bond between atoms. Let's form a bond, the two hydrogen atoms are bonded to the oxygen so the oxygen is in the medium. Remember, in the Lewis structure every bond requires a pair of electrons. Therefore, we used 4 of the available 8 electrons to form the bonds, We must now fill in the external energy levels. Two hydrogen atoms need only two electrons. So it is full, but oxygen on the other hand needs 8 electrons, So we pair the remaining electrons around it to complete the fitting.
Finally, the Lewis formula uses lines to represent covalent bonds. So we put it in place of the bonding electrons and we get it. Water has two covalent bonds in the form of single pairs, which is simple. In fact, it may be more difficult. Let's move to carbon dioxide, which is another very important molecule on our planet. Carbon has 4 valence electrons, and every atom has oxygen 6, meaning that the total is 16 valence electrons. The two oxygen atoms are attached to the carbon, so it becomes carbon in the medium The bond occurs using 4 of the 16 electrons. These three atoms need 8 electrons, so they are filled in next. So all atoms now have 8 electrons, but if we look closely, It took 20 electrons to fill the outer shell, but there are only 16 electrons available. So what to do? When there are not enough electrons to fill all the 8 groups with normal sharing The atoms have to share more of them, and in this case, they form a double bond By placing two pairs of electrons, for a total of 4 between each pair of atoms.
The 4 bonding electrons have a role in achieving the octet rule for both atoms. So we need fewer single pairs to fill in the octets. Double bonds allow us to use only 16 electrons. Replace the links with double lines, and the Lewis assembly is complete With two double bonds and a single pair on each oxygen. That was a little strange, of course we can do something as simple as molecular nitrogen, Two nitrogen atoms are bound together, right? Nitrogen has 5 valence electrons They are two atoms, meaning that the total is 10 electrons, so let's put the bond and complete the group of eight And it has 14 electrons. We don't have that many electrons. We can try a double bond, but this takes 12 electrons, which is more than we have two electrons. So we still have a shortage of electrons, let's go a little further And make it a triple bond, This is when the atoms share 3 pairs of electrons, which works well.
Only 10 electrons, but every atom has eight electrons. We switch the bond lines and it's done, a triple bond and a lone pair on each atom. This is what makes molecular nitrogen broken down to make compost and the like. And in case you were wondering, 3 is the upper limit for links. There is no quadruple covalent bond. So, this is the Lewis model, separate bonds that are formed by sharing certain electrons. It's a good model, and it's very close to the modern definition of covalent bond But it's still oversimplified and unfortunately, not 100 percent accurate. But the good about models is that even when they're partially wrong We can build on the right parts of it to make better models. This is what Linus Pauling did.
While he was at the university He read Gilbert Lewis's paper on chemical bonds that was published 3 years ago, He inspired Lewis Bowling's model to spend the rest of his life studying relationships Between the properties of materials and their molecular structure. After receiving his doctorate in physical chemistry, he traveled to Europe To study the new field of quantum mechanics with great physicists As Arnold Summerfield, Niels Bohr, and Erwin Schrodinger. Quantum mechanics, in short, is about the idea that some things, like light and electrons, They are particles and waves of energy.
Pauling applied a quantum mechanical model to chemical bonds. This was the birthplace of the connectivity model we know today Which visualizes chemical bonds as a kind of interference between the electron clouds of individual atoms And it's not just a simple sharing of electrons. We'll explore this in more detail when we talk about atomic orbits. But this is the model of electrons holding atoms together that I mentioned at the beginning of the loop What we take for granted today. Pauling's contributions to the model of chemical bonds had a huge impact on how we understand the universe So much so, that he won a Nobel Prize for it in 1954. That might not sound very impressive today But imagine discovering this when it was the only concept of atoms It is small bits of matter, as it was for Newton, Or even just a vague notion of charges in an atom, as it was for Brazilias. It is amazing. Our ability to understand chemistry is a direct result For models developed by scholars such as Lewis and Bowling, So, I thank them. And thank you for watching this episode of Crash Course Chemistry.
I think you are all model students. If you were paying attention today, you knew that a model is anything that represents something else in a different way. We often learn a lot when we try to understand why things don't work the way we expect them to. And that we can build new models on the basis of old models. You also learned that the quantum mechanics correlation model developed by Linus Pauling is essential to our understanding of chemistry And for the universe, you also learned how to draw a Lewis composition. This episode of Crash Course Chemistry was written by Eddie Gonzalez and edited by Blake De Pastino.
The chemistry consultant is Dr. Haiku Langer. This episode was filmed, edited and directed by Nicholas Jenkins. Our script moderator and sound designer is Michael Aranda, And the graphics team is of course Thought Café..