When two or more atoms enter into chemical bonds with each other, molecules arise. It does not matter if these atoms are the same or whether they are completely different from each other both in shape and in size. We will figure out what is the size of the molecules and what it depends on.
What are molecules?
For millennia, scientists have been pondering the mystery of life, what exactly happens when it begins. According to the most ancient cultures, life and everything in this world consists of the basic elements of nature - earth, air, wind, water and fire. However, over time, many philosophers began to put forward the idea that all things consist of tiny, indivisible things that cannot be created and destroyed.
However, only after the advent of atomic theory and modern chemistry did scientists begin to postulate that particles taken together gave rise to the basic building blocks of all things. So the term appeared, which in the context of modern particle theory refers to the smallest units of mass.
By its classical definition, a molecule is the smallest particle of a substance that helps preserve its chemical and physical properties. It consists of two or more atoms, as well as groups of identical or different atoms held together by chemical forces.
What is the size of the molecules? In the 5th grade, natural science (a school subject) gives only a general idea of the sizes and forms, this question is studied in more detail in high school in chemistry classes.
Molecule Examples
Molecules can be simple or complex. Here are some examples:
- H 2 O (water);
- N 2 (nitrogen);
- O 3 (ozone);
- CaO (calcium oxide);
- C 6 H 12 O 6 (glucose).
Molecules consisting of two or more elements are called compounds. So, water, calcium oxide and glucose are compound. Not all compounds are molecules, but all molecules are compounds. How big can they be? What is the size of the molecule? The fact is known that almost everything around us consists of atoms (except for light and sound). Their total weight will be the mass of the molecule.
Molecular mass
Speaking about the size of the molecules, most scientists are repelled by molecular weight. This is the total weight of all atoms included in it:
- Water, consisting of two hydrogen atoms (having one unit of atomic mass) and one oxygen atom (16 units of atomic mass), has a molecular weight of 18 (more precisely, 18.01528).
- Glucose has a molecular weight of 180.
- DNA, which is very long, can have a molecular weight of about 1010 (the approximate weight of one human chromosome).
Measurement in nanometers
In addition to mass, we can also measure the size of molecules in nanometers. The unit of water is about 0.27 Nm across. DNA reaches 2 Nm across and can stretch to several meters in length. It is difficult to imagine how such dimensions can fit in one cell. The ratio of length and thickness of DNA is amazing. It is 1/100 million, it's like a human hair with a length of a football field.
Shapes and sizes
What is the size of the molecules? They come in different shapes and sizes. Water and carbon dioxide are among the smallest, while proteins are among the largest. Molecules are elements made up of atoms that are linked together. Understanding the appearance of molecules is traditionally part of chemistry. Besides their incomprehensibly strange chemical behavior, one of the important characteristics of molecules is their size.
Where can the knowledge of the size of the molecules be especially useful? The answer to this and many other questions helps in the field of nanotechnology, since the concept of nanorobots and intelligent materials necessarily deals with the effects of molecular sizes and shapes.
What is the size of the molecules?
In Grade 5, natural science on this topic gives only general information that all molecules are composed of atoms that are in constant random motion. In high school, you can already see structural formulas in chemistry textbooks that resemble the actual form of molecules. However, it is impossible to measure their length using an ordinary ruler, and to do this, you need to know that the molecules are three-dimensional objects. Their image on paper is a projection onto a two-dimensional plane. The length of the molecule is changed by using the relationships of the lengths of its angles. There are three main ones:
- The angle of the tetrahedron is 109 °, when all bonds of this atom with all other atoms are single (only one dash).
- The angle of the hexagon is 120 °, when one atom has one double bond with another atom.
- The angle of the line is 180 °, when the atom has either two double bonds or one triple bond with another atom.
Real angles often differ from these angles, since it is necessary to take into account a number of various effects, including electrostatic interactions.
How to imagine the size of molecules: examples
What is the size of the molecules? In grade 5, the answers to this question, as we have already said, are general. Students know that the size of these compounds is very small. For example, if you turn a molecule of sand in one single grain of sand into a whole grain of sand, then under the resulting mass it would be possible to hide a house of five floors. What is the size of the molecules? The short answer, which is also more scientific, has the following form.
Molecular mass is equal to the ratio of the mass of the whole substance to the number of molecules in the substance or the ratio of the molar mass to the Avogadro constant. The unit of measure is a kilogram. The average molecular weight is 10 -23 -10 -26 kg. Take water, for example. Its molecular weight will be 3 x 10 -26 kg.
How does the size of a molecule affect gravity?
Responsible for the attraction between molecules is the electromagnetic force, which manifests itself through the attraction of opposite and repulsion of such charges. The electrostatic force that exists between opposing charges dominates the interactions between atoms and between molecules. The gravitational force is so small in this case that it can be neglected.
In this case, the size of the molecule affects the force of attraction through the electron cloud of random distortions arising from the distribution of electrons of the molecule. In the case of non-polar particles exhibiting only weak van der Waals interactions or dispersion forces, the size of the molecules directly affects the size of the electron cloud surrounding the molecule. The larger it is, the larger is the charged field that surrounds it.
A larger electron cloud means that more electronic interactions can occur between neighboring molecules. As a result, one part of the molecule develops a temporary positive partial charge, and the other negative. When this happens, the molecule can polarize the electron cloud in the neighboring one. Attraction occurs because the partial positive side of one molecule is attracted to the partial negative side of the other.
Conclusion
So what is the size of the molecules? In natural science, as we have found, you can find only a figurative idea of the mass and size of these smallest particles. But we know that there are simple and complex compounds. And the second can include such a thing as a macromolecule. This is a very large unit, for example a protein, which is usually created by polymerization of smaller subunits (monomers). They usually consist of thousands of atoms or more.
The most common macromolecules in biochemistry are biopolymers (nucleic acids, proteins, carbohydrates and polyphenols) and large non-polymer molecules (such as lipids). Synthetic macromolecules include conventional plastics and synthetic fibers, as well as experimental materials such as carbon nanotubes.