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The universe is made up of matter, and 98% of this matter (excluding dark matter) is composed of hydrogen and helium. However, billions of years ago, supergiant stars fused these elements to create all the other elements and then exploded them throughout the universe, giving rise to chemistry.

These elements combined to form a vast array of different molecules, and these molecules combined with each other in an incredible number of complex ways. Chemistry is the study of this matter in all its forms and how it interacts. It ranges from simple atoms to complex biological molecules such as proteins and DNA. It is a vast, fascinating, and complex subject, and this video is a condensed version of that.

History of Chemistry

Humans have had an interest in chemistry for a very long time. We wouldn't be what we are today if it wasn't for the chemical reaction of fire. We used this reaction to develop other chemical techniques, such as cooking food, making metal from ores, and making glass, among many others.

Since then, many advances in human civilisation have been built on the back of advances in chemistry. These include metalworking, manufacturing fertiliser, and creating new materials and drugs.

What is Chemistry?

Let's look at what falls under the umbrella of chemistry. Firstly, there is matter and all the different things matter is made of. At the very smallest scale, we start with atoms and the periodic table, which organises all the different types of atom, called chemical elements. Elements in each column have similar chemical properties.

Atoms are made of protons and neutrons in the nucleus, surrounded by electrons. Most of chemistry is due to how these electrons behave. By joining together atoms, we get molecules, and different kinds of molecules are called chemical compounds. Chemical compounds usually have very different chemical properties to the elements they are made from.

For example, hydrogen is very explosive, while oxygen is very burny. However, when you combine them into H2O, you get water, the least explosive and burny thing around. Compounds don't have to be made of single molecules. Many solids like metals or salts have a crystal structure, made of repeating groups of atoms called unit cells. If you have several substances together, you have a mixture, like the air around you or a cake.

Now let's move onto how atoms stick together with the very important subject of bonding. Atoms bond together in several different ways to reduce their combined energy by stealing or sharing electrons or moving them into different configurations. A universal rule in science is that everything is always trying to minimise their energy, and bonding is one way that atoms achieve this.

Understanding how energy moves around in chemical substances is vital to understand when reactions will or will not happen. For example, wood won't react with oxygen to start burning spontaneously, but if you give it enough energy to begin with, it will. Another example where energy is very important is where you can speed up a reaction between two other compounds by introducing a catalyst. The catalysts make it more energetically favourable, speeding up the reaction.

Energy also determines when compounds will exist in different forms: solid, liquid, or gas. Which form they will be found in comes from the temperature they are at and the pressure they are under. The values vary for each material, but in general, things are solid at low temperature and/or high pressure, and gas at high temperature and low pressure.

Another really interesting form of matter is a plasma, which is where you rip electrons off atoms in a gas to make them into ions. This is what is used to make neon lights.

Reactions

Chemical reactions form the core of chemistry: which compounds react with each other, why they react, and what is left over after a reaction. There are many different kinds of reaction which can be categorised in different ways. All of these reactions are governed by a set of fundamental rules called chemical laws. The foundation of these laws is the conservation of mass and energy, which means that no matter or energy is created or destroyed in a chemical reaction, they just change to different forms.

Kinetics is the study of how fast reactions happen and the things that control what the reaction rates are. A reaction where electrons are transferred from one reactant to another is called an Oxidation-Reduction reaction, or a redox reaction for short. Oxidation means a loss of electrons from a substance, while reduction means the gain of electrons, and they have to happen together. An example is sodium and chlorine, where chlorine is the reducing agent and sodium is the oxidising agent.

Another important property of substances is their pH, whether they are an acid or a base. There are several theories to model acid-base reactions, but one way to think about it is that acids are substances that have a hydrogen ion ready to give up in a chemical reaction, and a base is a substance that takes a hydrogen ion.

If there are a number of different chemical compounds which can react with each other back and forth, there can be swings between one substance and another. Equilibrium is where the amount of each substance is constant, even though a reaction may still be taking place. This can also happen in phases changes like from solid to liquid or liquid to gas. This is the study of equilibrium.

So those are the basics of chemistry. Research in chemistry looks at how these rules apply in different chemical systems. Now I'm going to move on to look at the different fields in chemistry.

Theoretical Chemistry

Theoretical chemistry attempts to explain the structures of atoms and molecules and how they interact using mathematical methods. It is very closely related to theoretical physics and quantum chemistry, and often uses techniques in computational chemistry where atoms, molecules, and reactions are simulated in a computer.

Simulating the proper quantum behaviour of anything more complicated than a hydrogen atom is very difficult or impossible for multiple bodies. So many cutting edge techniques in computer science are used to try and simulate molecules and how they interact with each other. In fact, this is one of the most exciting applications of quantum computers because they would be able to directly simulate chemical systems, and would help with things like discovering novel materials and drugs and a whole lot more.

Physical Chemistry

Physical chemistry studies chemical systems in terms of their physics, so things like energy, force, time, motion, thermodynamics, quantum properties, amongst others. There are many sub-fields, like looking at the electronic properties in Electrochemistry, which is important for developing better batteries or Materials Science, which is trying to create materials with new properties like extreme strength, durability, or self-healing. This is a critical problem with building Earth based nuclear fusion reactors which are reliant on new materials.

Analytical Chemistry

Analytical chemistry is like detective work. You've got a sample of something and you need to work out what it is made of, and the amount of the different components. Chemists have developed a huge array of techniques to probe and measure different properties of different materials. Traditional techniques involve wet chemical techniques, like precipitation which separates compounds depending on what temperature they evaporate. There's also a huge array of modern techniques like chromatography where different compounds move at different speeds through a solution and so separate. Or the many different kinds of spectroscopy, that can detect materials by shining light on them, or mass spectrometry where the materials are flung though electric or magnetic fields to separate them according to their masses.

Organic and Biochemistry

And finally we get to the huge fields of Inorganic, Organic, and Biochemistry. Organic and Biochemistry look at the chemistry of living things and Inorganic chemistry looks at everything else, although there is still a large amount of crossover. Most of the inorganic compounds that are studied are man-made, and a lot of the motivation is to find chemicals with new properties that can be used in the chemical industry and the wider world. In fact, there are very few areas of human endeavour where inorganic chemistry has not been used in some way. There is medicine and agriculture, special fluids like detergents or emulsifiers, special coatings, materials, pigments or fuels for many industrial purposes. Within chemical production itself, catalysts are very important as they speed up other chemical reactions. Inorganic chemistry also bleeds into materials science making solids with novel crystal structures like high temperature superconductors for example. The list is endless.

Now between inorganic and organic chemistry sits organometallic chemistry. This looks at organic compounds chemical which are bonded with a metal, and are typically used in reactions in the chemical industry often as catalysts.

Organic chemistry looks at the structure and behaviour of the molecules of life which are typically built from a small set of different atoms: carbon, hydrogen, oxygen and nitrogen, plus a few others. Organic chemists also look at making new organic compounds with useful properties. Organic molecules all contain carbon and the carbon hydrogen bond is the most common structure in organic chemistry.