Many elements, compounds, and mixtures have played a major role in creating life on Earth. One would undoubtedly tell about water after air, oxygen, carbon, hydrogen, and nitrogen.
The most common material found on Earth is water that makes up only 0.05% of the planet’s mass but covers, in the form of liquid and ice, more than 70% of its surface.
Yet water is the most unusual substance and a great mystery that keeps surprising researchers and scientists with its unique properties.
So what is water? Is it a compound? First, we need to know what a compound is and its features. Then we can understand what exactly water is.
A compound is defined as the substance resulting from the combination of two or more elements according to a well-defined quantitative relationship.
This ratio indicates the number of elements present in the compound. It also specifies the numerical balance between the atoms presents within the combination.
Thus, the composition that characterizes each compound must be rigidly constant; otherwise, except in rare cases, one could not speak.
The smallest constituent unit of a compound is a molecule; a molecule, however, is not necessarily a compound: in fact, it is sometimes made up of atoms of the same element.
Properties of compound
A compound has the following properties:
1. A compound is a substance that results from the union of two or more chemical elements, combined in exact and fixed amounts through chemical bonds.
2. All molecules in a compound have the same combination of elements.
3. The properties of compounds are different from those of the elements that make them up. Each combination has a definite name and a formula. This formula indicates how many atoms of each ingredient the compound has.
4. A compound’s elements cannot be separated by physical processes (decantation, filtration, distillation) but by chemical methods.
5. The physical properties depend mainly on the bond’s type that holds a molecule’s atoms together. These can indicate the type of structure and predict its physical properties.
6. Under ambient conditions, compounds are found in either three physical states (solid, liquid, and gas).
Water- a compound
Based on the properties of the compound mentioned above, we can easily say water is a compound. Why? Look at the explanation below. The French chemist Antoine Lavoisier found that water is made up of two elements: hydrogen and oxygen.
Lavoisier introduced the name oxygen in 1778 and hydrogen in 1783. He gave hydrogen its name, which means a water generator.
In 1804, another French chemist, Joseph Gay-Lussac, and the German naturalist Alexander von Humboldt demonstrated that the water molecule consists of two hydrogen atoms for each oxygen atom, forming the ubiquitous chemical formula H 2 O.
Covalent bonds link these elements. Until then, everyone thought the water was a single element. The water molecule has a non-linear structure. The atoms distribution and the high-value oxygen electronegativity generate the formation of a dipole that signifies the polarity of the water.
This characteristic makes the water have good electrical conductivity. Water is the universal solvent since the vast majority of substances can be dissolved in it.
It has an enormous adhesive quality, which is the reason why it can wet objects and bodies, thanks to the polarity of its molecules. And, in addition, it is an excellent conductor of electricity and heat.
Properties of Water
Water is a compound of paramount importance to life with exceptional properties due to its composition and structure. The chemical properties of water are:
1. Its chemical formula is H₂O: one oxygen atom linked to two hydrogens.
According to the first property of the compound mentioned above, water is composed of two hydrogen atoms and one oxygen atom, which is a fixed ratio for water formation.
The two-element atoms unite through a covalent bond, thereby forming water.
2. To form a water molecule (H 2 O), an oxygen atom joins two hydrogen atoms, sharing their electrons.
Each of the two hydrogen atoms shares its single electron with the oxygen atom in its outer covering to fill the two empty spaces, thus completing the shell with 8 electrons while forming two covalent bonds.
In this way, each hydrogen atom is filled with two electrons in its unique shell, and each oxygen atom is filled with eight electrons on its outer surface.
The two covalent bonds (between the O and H atoms) hold the molecule together. It proves that water molecules, like all molecules in a compound, have the same elements.
3. Though water is formed by hydrogen and oxygen atoms, the properties of water, hydrogen, and oxygen are different from each other. Hydrogen refers to both a chemical element and a simple substance.
The element hydrogen is made up of hydrogen atoms. Under normal conditions, hydrogen is a colorless and odorless gas. In small quantities, it is non-toxic.
Solid hydrogen melts at –259 ° C and liquid hydrogen boils at –253 ° C. Low melting and boiling points, a minimum temperature range for the existence of liquid hydrogen (only 6 ° ).
Like hydrogen, oxygen is also an element. Under normal conditions, oxygen is a colorless and odorless gas. Solid oxygen melts at –218 ° C, and liquid oxygen boils at –183 ° C.
Water, on the other hand, boils at 100 ° C and freezes at 0° C. It indicates that water has the third property of the compound listed above.
4. Water molecules are splittable through the process called the electrolysis of water. It is an electrolytic process in which the passage of electric current causes the breakdown of water into oxygen and gaseous hydrogen.
In 1790 the scholars Jan Rudolph Deiman and Adriaan Paets van Troostwijk managed to decompose the water by generating sparks with the help of pure gold threads.
In 1866 August Wilhelm von Hofmann invented the Hofmann voltmeter, an apparatus for electrolysis of water, which also allows the measurement of the quantity of oxygen and hydrogen developed during the process.
In 1888 Dmitry Lachinov developed a method that made it possible to carry out water electrolysis even in the industrial field.
It suggests that water is a compound as a water molecule is breakable through a chemical process only like all the other compounds.
5. Due to its structure, water is a prototypical compound for forming so-called hydrogen bonds.
Two partially negatively charged atoms interact in a hydrogen bond, indirectly attracting each other through a partially positively charged hydrogen atom.
The hydrogen atom, which functions as a bridge, is covalently bonded (sharing electrons) to an electronegative atom such as oxygen or nitrogen.
The intrinsic polarity of such a bond makes it possible for the hydrogen atom to feel an electrostatic attraction exerted by a second electronegative atom, which is located in another molecule.
The electronegative atom is covalently bonded to hydrogen in a hydrogen bond, known as the donor atom. The other electronegative atom is known as the acceptor of the hydrogen bond.
As suggested on the fifth property of the compound, water molecules are formed by the hydrogen bond, thus proving that water is a compound.
6. Under ambient conditions, water is found in a liquid state as in lakes, seas, and oceans. However, water is the only compound on Earth that is present in all three forms of matter.
Thus, water is present in the solid-state, liquid form, and gaseous state. The three phases are solid (ice or snow), liquid (water), and gaseous (water vapor).
- Solid–state: The particles in a solid are strongly bound together. Ice cubes keep their shape regardless of the container that contains them. It is because the oxygen atom of each water molecule participates in the formation of two hydrogen bonds with neighboring water molecules. The hydrogen bonds lead to an arrangement of water molecules that touch each other with their opposite poles. The molecules form layers, each of which is associated with three molecules belonging to the same layer and one from an adjacent layer. The ice structure belongs to minor dense systems; there are voids in it, the dimensions of which are somewhat more prominent than the size of the molecule.
- Liquid state: The bond between the molecules is broken, and the water can thus take the shape of the container that contains it. However, the hydrogen bonds between the molecules are preserved: associates consisting of a larger or smaller number of water molecules. However, unlike ice, each associate exists for a short time. The destruction of some and the formation of other aggregates constantly occurs.
- Gas state: The water vapor occupies the entire space in the container. The distances between molecules are great, and gas is thus compressible. When water is heated, part of the heat is spent on breaking hydrogen bonds (the energy of breaking a hydrogen bond in water is about 25 kJ / mol. Hydrogen bonds between water molecules are entirely broken only when water passes into steam.
Thus, it suggests that water is found in all three states, thereby fulfilling the sixth property of the compound.
Water is a compound, but it is a chemical compound that is broken only through electrolysis. The properties of this small compound of only three atoms are determined by a specific molecular arrangement and a particular electronic distribution.
As we have seen, the chemical properties of water are very particular and define a unique case among all chemical substances. These properties have enormous relevance in determining the world in which we live.
There is no doubt that our reality would be very different if we were not organisms based, at all levels, on our coexistence with water.