The Second Step On The Path To Matter: Molecules

What is it that makes the objects you see in your surroundings different from each other? What is it that discriminates their colours, shapes, smells, and tastes? Why is one substance soft, another hard, and yet another fluid? From what you have read so far, you may answer these questions saying, "The differences between their atoms do this". Yet, this answer is not sufficient, because if the atoms were the cause for these differences, then there would have to be billions of atoms bearing different properties from each other. In practice, this is not so. Many materials look different and bear different properties although they contain the same atoms. The reason for this is the different chemical bonds the atoms form among them to become molecules.
On the way to matter, molecules are the second step after atoms. Molecules are the smallest units determining the chemical properties of matter. These small bodies are made up of two or more atoms and some, of thousands of groups of atoms. Atoms are held together inside molecules by chemical bonds determined by the electromagnetic force of attraction, which means that these bonds are formed on the basis of the electrical charges of the atoms. The electrical charges of atoms, in turn, are determined by the electrons on their outermost shell. The arrangements of molecules in different combinations give rise to the diversity of matter we see around us. The importance of the chemical bonds that lie at the heart of the diversity of matter come forward at this very point.
 

Chemical Bonds

As explained above, chemical bonds are formed through the motion of electrons in the outermost electron shells of the atoms. Each atom has a tendency to fill up its outermost shell with the maximum number of electrons it may shelter. The maximum number of electrons the atoms can hold in their outermost shells is 8. To do this, atoms either receive electrons from other atoms to complete the electrons in their outermost shells to eight, or if they have lesser electrons in their outermost shells, then they give these to another atom, making a sub-shell that had previously been completed in their outermost orbits. The tendency of the atoms to exchange electrons constitutes the basic inciting force of the chemical bonds they form between each other.
This driving force, that is, the objective of the atoms to raise the number of electrons in their outermost shells to maximum, causes an atom to form three types of bonds with other atoms. These are the ionic bond, covalent bond and metallic bond.
Commonly, special bonds categorised under the general title of "weak bonds" act between molecules. These bonds are weaker than the bonds formed by atoms to constitute molecules because molecules need more flexible structures to form matter.
Let us now, in brief, see the properties of these bonds and how they are formed.

Ionic Bonds

Atoms combined by this bond swap electrons to complete the number of electrons in their outermost shells to eight. Atoms having up to four electrons in their outermost shells give these electrons to the atom with which they are going to combine, that is, with which they will bond. Atoms having more than four electrons in their outermost shells receive electrons from the atoms with which they will bond. Molecules formed by this type of bond have crystal (cubic) structures. Familiar table salt (NaCl) molecules are among substances formed by this bond. Why do atoms have such a tendency? What would happen if they did not have it?

The sodium atom gives its outermost electron to a chlorine atom and becomes positively charged. Receiving the electron, the chlorine atom becomes negatively charged. The two form an ionic bond through these two opposite charges attracting each other.24

Until today, the bonds formed by atoms could be defined only in very general terms. It has not yet been understood why atoms adhere to this principle. Could it be that atoms decide by themselves that the number of electrons in their outermost shells should be eight? Definitely not. This is such decisive behaviour that it goes beyond the atom, because it has no intellect, will, or consciousness. This number is the key in the combination of atoms as molecules that constitute the first step in the creation of the matter, and eventually, the universe. If atoms did not have such a tendency based on this principle, some vital molecules would not exist. Yet, from the first moment they were created, atoms have been serving in the formation of molecules and matter in a perfect manner thanks to this tendency.

Covalent Bonds

Scientists who studied the bonds between atoms faced an interesting situation. While some atoms swap electrons for bonding, some of them share the electrons in their outermost shells. Further research revealed that many molecules that are of critical importance for life owe their existence to these 'covalent' bonds.

Some atoms form new molecules by covalent bonding, sharing the electrons in their outer orbits.25

Let us give a simple example to explain covalent bonds better. As we mentioned previously on the subject of electron shells, atoms can carry a maximum of two electrons in their innermost electron shells. The hydrogen atom has a single electron and it has the tendency to increase the number of its electrons to two to become a stable atom. Therefore, the hydrogen atom forms a covalent bond with a second hydrogen atom. That is, the two hydrogen atoms share each other's single electron as a second electron. Thus, the H₂ molecule is formed.
 

Metallic Bonds

If a large number of atoms come together by sharing each others' electrons, this is called a "metallic bond". Metals like iron, copper, zinc, aluminium, etc., that form the raw material of many tools and instruments we see around us or use in daily life, have acquired a substantial and tangible body as a result of the metallic bonds formed by the atoms constituting them.

The bonds between metal atoms are very different from other forms of chemical bonding – each metal atom contributes its outer electrons to a common pool. This "sea of electrons" explains a key property of metals – their ability to conduct electricity.26

Scientists are not able to answer the question as to why electrons in the electron shells of the atoms have such a tendency. Living organisms, most interestingly, owe their existence to this tendency.

The Next Step: Compounds

A compound is a pure substance formed when two or more atoms combine through a chemical reaction. Molecules are the basic building blocks of compounds.
In laboratories, new compounds are produced everyday. Currently, it is possible to talk about almost two million compounds. The simplest chemical compound can be as small as the hydrogen molecule, while there are also compounds made up of millions of atoms.27

The Raw Materials of the Universe and the Periodic Table: 92 elements found freely in nature and 17 elements formed artificially in laboratories or in nuclear reactions are arranged in a table called the "Periodic Table" according to the number of their protons. At first look, the Periodic Table may appear to be a bunch of boxes containing one or two letters with numbers at the top and bottom corners. Most interestingly, however, this table accommodates the elements of the entire universe including the air we breathe, as well as of our bodies.

How many different compounds can an element form at most? The answer to this question is quite interesting because, on the one hand, there are certain elements that do not interact with any others (inert gases), while, on the other hand, there is the carbon atom that is able to form 1,700,000 compounds. As stated above, the total number of compounds is about two million. 108 elements out of the total of 109 form 300,000 compounds. Carbon, however, forms 1,700,000 compounds all by itself in a most amazing fashion.