2. Branches of Chemistry


Inorganic chemistry is the study of the properties and behaviour of inorganic compounds.

It covers all chemical compounds except organic compounds.

Inorganic chemists study things such as crystal structures, minerals, metals, catalysts, and most elements in the Periodic Table.

Branches of inorganic chemistry include:

  • Bioinorganic chemistry — the study of the interaction of metal ions with living tissue, mainly through their direct effect on enzyme activity.
  • Geochemistry — the study of the chemical composition and changes in rocks, minerals, and atmosphere of the earth or a celestial body.
  • Nuclear chemistry — the study of radioactive substances.
  • Organometallic chemistry — the study of chemical compounds containing bonds between carbon and a metal.
  • Solid-state chemistry — the study of the synthesis, structure, and properties of solid materials.
2. Branches of Chemistry


Organic chemistry involves the study of the structure, properties, and preparation of chemical compounds that consist primarily of carbon and hydrogen.

Organic chemistry overlaps with many areas including

  • Medicinal chemistry —the design, development, and synthesis of medicinal drugs. It overlaps with pharmacology (the study of drug action).
  • Organometallic chemistry — the study of chemical compounds containing bonds between carbon and a metal.
  • Polymer chemistry — the study of the chemistry of polymers.
  • Physical organic chemistry — the study of the interrelationships between structure and reactivity in organic molecules.
  • Stereochemistry — the study of the spatial arrangements of atoms in molecules and their effects on the chemical and physical properties of substances.
2. Branches of Chemistry

The scope of chemistry

The days are long past when one person could hope to have a detailed knowledge of all areas of chemistry. Those pursuing their interests into specific areas of chemistry communicate with others who share the same interests. Over time a group of chemists with specialized research interests become the founding members of an area of specialization. The areas of specialization that emerged early in the history of chemistry, such as organic, inorganic, physical, analytical, and industrial chemistry, along with biochemistry, remain of greatest general interest. There has been, however, much growth in the areas of polymer, environmental, and medicinal chemistry during the 20th century. Moreover, new specialities continue to appear, as, for example, pesticide, forensic, and computer chemistry.

2. Branches of Chemistry


chemistry, the science that deals with the properties, composition, and structure of substances (defined as elements and compounds), the transformations they undergo, and the energy that is released or absorbed during these processes. Every substance, whether naturally occurring or artificially produced, consists of one or more of the hundred-odd species of atoms that have been identified as elements. Although these atoms, in turn, are composed of more elementary particles, they are the basic building blocks of chemical substances; there is no quantity of oxygen, mercury, or gold, for example, smaller than an atom of that substance. Chemistry, therefore, is concerned not with the subatomic domain but with the properties of atoms and the laws governing their combinations and how the knowledge of these properties can be used to achieve specific purposes.

The great challenge in chemistry is the development of a coherent explanation of the complex behaviour of materials, why they appear as they do, what gives them their enduring properties, and how interactions among different substances can bring about the formation of new substances and the destruction of old ones. From the earliest attempts to understand the material world in rational terms, chemists have struggled to develop theories of matter that satisfactorily explain both permanence and change. The ordered assembly of indestructible atoms into small and large molecules, or extended networks of intermingled atoms, is generally accepted as the basis of permanence, while the reorganization of atoms or molecules into different arrangements lies behind theories of change. Thus chemistry involves the study of the atomic composition and structural architecture of substances, as well as the varied interactions among substances that can lead to sudden, often violent reactions.

Chemistry also is concerned with the utilization of natural substances and the creation of artificial ones. Cooking, fermentation, glass making, and metallurgy are all chemical processes that date from the beginnings of civilization. Today, vinyl, Teflon, liquid crystals, semiconductors, and superconductors represent the fruits of chemical technology. The 20th century saw dramatic advances in the comprehension of the marvelous and complex chemistry of living organisms, and a molecular interpretation of health and disease holds great promise. Modern chemistry, aided by increasingly sophisticated instruments, studies materials as small as single atoms and as large and complex as DNA (deoxyribonucleic acid), which contains millions of atoms. New substances can even be designed to bear desired characteristics and then synthesized. The rate at which chemical knowledge continues to accumulate is remarkable. Over time more than 8,000,000 different chemical substances, both natural and artificial, have been characterized and produced. The number was less than 500,000 as recently as 1965.

Intimately interconnected with the intellectual challenges of chemistry are those associated with industry. In the mid-19th century the German chemist Justus von Liebig commented that the wealth of a nation could be gauged by the amount of sulfuric acid it produced. This acid, essential to many manufacturing processes, remains today the leading chemical product of industrialized countries. As Liebig recognized, a country that produces large amounts of sulfuric acid is one with a strong chemical industry and a strong economy as a whole. The production, distribution, and utilization of a wide range of chemical products is common to all highly developed nations. In fact, one can say that the “iron age” of civilization is being replaced by a “polymer age,” for in some countries the total volume of polymers now produced exceeds that of iron.

1. Introduction and basic guide

What is radioactivity?

Radioactive decay, or radioactivity, is basically a process in which an unstable nucleus loses energy by the emission of radiation in the form of a particle.

This is more of a physics concept than a basic chemistry concept, but it is very relevant for chemists.

Not all atoms that exist are stable, some are what you could call “not meant to be”. Most of the matter that we see is made up of combinations of protons, neutrons that are stable (stable atoms, specifically, stable nuclei). But other combinations of neutrons and protons give rise to unstable nuclei, that eventually fall apart. This is the basis of radioactivity in simple terms.

During the decomposition of these unstable atoms, energy is released in the form of particles. This release of energy can be detected, and it is what we call radiation. When this process takes place, a new nucleus is formed, and therefore, a new atom. This new atom can be also unstable and keep releasing radiation until it turns into an stable atom, which no longer emits energy as radiation.

1. Introduction and basic guide

What is oxidation and reduction in chemistry?

Redox processes are a type of chemical reaction in which one of the reacting compounds gets oxidized and the other gets reduced. A redox reaction involves a transfer of electrons. We say that a compound, or atom within a compound, gets oxidized when it loses electrons and the other component gets reduced when it gains electrons.

One of the most typical examples of a redox process is the rusting of iron. Iron metal, Fe0 (oxidation state = 0) reacts with oxygen from air, O2 (oxidation state = 0) to give rust, or iron (III) oxide, Fe2O3.

4 Fe0 (solid) + 3 O2  (gas) → 2 Fe2O3 (solid)

In this new compound, the new oxidation state of iron is +3. Iron has lost 3 electrons, therefore, getting oxidized:

Fe0 → Fe3+ + 3 e

On the other hand, the new oxidation state of oxygen is -2. Each oxygen atom has gained two electrons, getting reduced:

O2 + 4 e → 2 O2-

A typical example of a redox process is an explosion in which the explosive compound gets oxidized violently. C4 is a common plastic explosive, much more energetic than dynamite. The main component of C4 is RDX (Research Development Explosive), also known as cyclonite or, according to IUPAC, 1,3,5-trinitro-1,3,5-triazinane.

The process of oxidation of RDX is thermodynamically favorable, and gives rise to a exothermic reaction, in which a large amount of energy is released in the form of heat and light, causing the explosion.

redox reactions are among the most basic chemistry concepts
Explosive oxidation of RDX from C4 explosives

The N–NO2 bonds are extremely unstable and prone to oxidation. That’s what makes this kind of compounds highly explosive.

1. Introduction and basic guide

What is stoichiometry?

Stoichiometry is a very basic chemistry concept. It is just a way of measuring or determining the amount of each substance that is involved in a reaction (reactants), and the amount of products that are generated.

Before actually running a reaction in the lab, a chemist needs to figure out what is the number of molecules of each reagent is required for the reaction to proceed. For this purpose, we use a unit called “mole”. The mole is the base unit of “amount of substance”. One mole accounts for 6.022·1023 molecules. We need it to be a huge number, since there is a huge number of molecules in each gram of any reagent of a reaction.

The stoichiometry of a reaction is the measurement of the relative quantities (or equivalents), measured in moles, of the reactants that are involved in the reaction.

For instance, each 2 molecules (or 2 moles) of hydrogen gas (H2) react with 1 molecule (or 1 mole) of oxygen gas (O2), to generate 2 molecules (or 2 moles) of water (H2O):

2 H2 (gas) + 1 O2 (gas) → 2 H2O (liquid)

So if we were to perform this (rather inpractical, using two expensive, difficult to handle gases, to get a cheap easy to find product such as water) reaction in a lab, we would have to mix together 2 moles of hydrogen per mole of oxygen. This means using 2 equivalents (equiv) of hydrogen respect to the amount of oxygen. In this case, while handling gases, the number of moles of each can be controlled by establishing a partial pressure for each of them.

In case of more common solid reagents, we can consider a hypotetical synthesis of sodium carbionate from carbonic acid. We need 2 equivalents of sodium hydride (NaH) per mole of carbonic acid employed (twice as many molecules of NaH than molecules of carbonic acid).

stoichiometry of sodium carbonate synthesis
Synthesis of sodium carbonate from carbonic acid

This would yield 1 equivalent, or 1 mole of sodium carbonate, and also release 2 equivalents (or 2 moles) of hydrogen gas as a byproduct.

1. Introduction and basic guide

What are acids and bases?

Following the original definition by Arrhenius, (1884), an acid is a compound that is able to release a hydrogen cation, or proton (H+). For example, molecules of hydrochloric acid (aqueous HCl) get ionized in solution giving a proton to water, through an acid-base equilibrium:

HCl (aq) + H2O (liquid) ⇌ H3O+ (aq) + Cl (aq)

HCl in water gives rise to hydronium cations and chloride anions. This is classical acid-base equilibrium.

On the other hand, bases, such as sodium hydroxide (NaOH), can catch protons from water, giving rise to hydroxide anions.

NaOH (aq) + H2O (liquid) ⇌ HO (aq) + Na+ (aq)

Whereas the Arrhenius acid-base model is very illustrative, it has its limitations, and other models are used to describe more advanced acid-base theories. The most important ones are the Brønsted-Lowry theory (which is a more general version of the Arrhenius theory), and the Lewis theory.

According to the Lewis theory, an acid is a substance that accepts a lone pair of electrons, and a base is a substance that donates a lone pair of electrons. This accounts for acid-base equilibria which cannot be explained by Arrhenius or Brønsted-Lowry theories, such as the basicity of ammonia in water:

:NH3 (aq) + H2O (liquid) ) ⇌ NH4+ (aq) + :OH (aq)

Relative acidity or basicity of solutions or mixtures is measured using a logarithmic scale called the pH scale. It generally goes from 0, most acidic (such as hydrochloric acid solutions), through pH = 7 (considered neutral), up to 14, most basic (such as water solutions of sodium hydroxide). Nevertheless, compounds more basic and acidic than those do exist, pH = 0–14 is definitely not a closed range. Examples of common solutions or mixtures of different pH are shown in the scale below.

acid-base pH scale is one of the most basic chemistry concepts
pH scale.
1. Introduction and basic guide

What is chirality and where does it come from?

Chirality is a geometric property of certain molecules. A molecule is said to be chiral when its mirror image is not superimposable to the molecule itself. The classical source of chirality in a (organic) compound is the presence of a carbon atom with four different substituents.

The origin of chirality, together with the origin of life is one of the most relevant questions in, not only chemistry, but science in general, so it is not possible to answer in a straightforward manner. The main theory backing it up is based on homochirality, which could have emerged over three steps: mirror-symmetry breaking, chiral amplification and chiral transmission. This is far beyond basic chemistry concepts.

1. Introduction and basic guide

Why do two chemical compounds react?

Chemistry studies changes in matter. A chemical reaction is a process in which one set of chemical compounds are transformed into another. Reaction occur when there is an interaction between the compounds in which some initial bonds are broken and some new bonds are formed.

Why does this happen? In simple terms, because the energy holding the new bonds together is higher than the energy that held the initial bonds. This is the definition of a thermodynamically favored process. Favorable thermodynamics is the most fundamental step that leads two compounds to react with each other. Other drastically important factor is reaction kinetics.