Key Types and Properties of Molecules Explained
A molecule definition, a group of two or more atoms that form the smallest recognizable unit into which the structure and chemical properties of that substance can be divided and preserved by a pure substance.
A molecule may be homonuclear, meaning that it consists of atoms of a single chemical component, as with oxygen (O2); or it may be heteronuclear, as with water, a chemical compound consisting of more than one component (H2O).
Atoms and Molecules
Atoms consist of a single nucleus of a positive charge surrounded by a cloud of negatively charged electrons. The electron clouds communicate with each other and with the nuclei as atoms touch each other closely. If this interaction is such that the system's total energy is reduced, then the atoms bind to form a molecule together. Thus, a molecule consists, from a structural point of view, of an arrangement of atoms held together by the forces of valence. Two atoms that are chemically bound comprise diatomic molecules.
Diatomic Molecules — Only two atoms, of the same or different chemical elements, are composed of a diatomic atom. O2 and CO are representations of diatomic molecules.
Heteronuclear Diatomic Molecules — A diatomic heteronuclear molecule consists of two combined atoms of the same substance. Carbon monoxide, hydrochloric acid (HCl), and hydrogen fluoride are examples of homonuclear diatomic molecules (HF)
Homonuclear Diatomic Molecules — A homonuclear diatomic molecule consists of two chemically fused atoms of different elements. . Seven diatomic elements are available: hydrogen (H2), nitrogen (N2), oxygen (O2), fluorine (F2), chlorine (Cl2), iodine (I2) and bromine (Br2). These seven elements are so reactive that they are most often found to be related to another atom of the same nature.
Molecular Mass
The sum of the atomic weights of its constituent atoms is the molecular weight of a molecule. If the molecular weight of a substance is M, then M grams of the substance is considered one mole. For all substances, the number of molecules in one mole is the same; this number is known as Avogadro's number (6.0221023). Through mass spectrometry and by techniques based on thermodynamics or kinetic transport processes, molecular weights can be calculated.
Water Molecule
The ratio of the number of atoms that can be bonded together to form molecules is fixed; each water molecule, for instance, contains two hydrogen atoms and one oxygen atom. Chemical compounds are differentiated from solutions and other mechanical mixtures by this characteristic. Hydrogen and oxygen can therefore be present in mechanical mixtures in any arbitrary proportion, but the chemical compound water can only combine in such amounts to form the chemical compound water (H2O). Here given the structure of water molecule -
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Polar Molecule
Shared electron pairs, or covalent bonds, keep molecules together. Such bonds are directional, which means that the atoms take particular positions relative to each other in order to maximize the strength of the bonds. As a consequence, each molecule has a definite structure, or spatial distribution of its atoms, which is fairly rigid.
Valence, which specifies how atoms join in definite ratios and how this is related to the bond directions and bond lengths, is concerned with structural chemistry. The properties of molecules are associated with their structures; the water molecule, for example, is structurally bent and thus has a dipole moment, Oxygen being electronegative pull electrons towards itself and attain a partial negative charge while the hydrogen atoms attain a partial positive charge which results in the formation of a polar molecule.
While the carbon dioxide molecule is linear and has no dipole moment and hence is a nonpolar molecule.
ATP Molecule
Adenosine triphosphate (ATP) is an organic compound and hydrotrope that provides energy in living cells to drive several processes, such as muscle contraction, the transmission of nerve impulses, dissolution of condensate, and chemical synthesis. ATP is also referred to as the "molecular unit of currency" of intracellular energy transfer found in all known forms of life.
ATP is known as a nucleoside triphosphate from a biochemical point of view, which means that it consists of three components: a nitrogen base (adenine), a ribose sugar, and triphosphate.
Biological Molecules
Substances that cells and living organisms produce are known as biological molecules or biological macromolecules. Biomolecules have a broad variety of structures and sizes and perform a wide range of functions. There are mainly four types of biological molecules- carbohydrate, lipids, proteins, and nucleic acids.
Among biomolecules, nucleic acids, namely DNA and RNA, have the unique role of storing the genetic code of an organism, the nucleotide sequence that specifies the protein sequence of amino acids that are critical to life on Earth.
Within a protein, there are 20 different amino acids that can occur; the order in which they occur plays a central role in deciding the structure and function of proteins.
Carbohydrates, which mainly consist of molecules containing carbon, hydrogen, and oxygen atoms, are critical sources of energy and structural components of all life and are among the most abundant biomolecules on Earth. They are composed of monosaccharides, disaccharides, oligosaccharides, and polysaccharides from four types of sugar units.
Lipids, another essential living organism biomolecule, perform a number of functions, including serving as a stored energy source and acting as chemical messengers.
Did You Know?
There are various methods to represent the molecular structure-
Element symbols represent atoms in Lewis structures, and dots represent electrons surrounding them. It is also possible to display a pair of mutual electrons (covalent bond) as a single dash. The ball-and-stick model better illustrates the spatial arrangement of the atoms. The Kekulé structure, in which each bond is represented by a slash, carbon atoms are implied where two or more lines intersect, and hydrogen atoms are typically omitted, is typical for aromatic compounds.
FAQs on What Is a Molecule in Chemistry?
1. What is a molecule in chemistry, and can you provide some common examples?
In chemistry, a molecule is defined as the smallest particle of a pure substance that can exist independently and retain its chemical properties. It consists of two or more atoms held together by strong chemical bonds. Molecules can be formed from atoms of the same element or different elements.
Common examples include:
- Water (H₂O): A molecule made of two hydrogen atoms and one oxygen atom.
- Oxygen (O₂): A molecule made of two oxygen atoms bonded together.
- Carbon Dioxide (CO₂): A molecule consisting of one carbon atom and two oxygen atoms.
2. What is the main difference between a molecule and a compound?
The primary difference lies in the composition of atoms. A molecule is a general term for any group of two or more atoms bonded together. A compound is a specific type of molecule that consists of two or more different elements chemically joined in a fixed ratio. Therefore, all compounds are molecules, but not all molecules are compounds. For example, a water molecule (H₂O) is also a compound, but an oxygen molecule (O₂) is not a compound because it is made of only one element.
3. What are the main types of molecules based on the atoms they contain?
Molecules can be broadly classified based on the types of atoms they are composed of:
- Homonuclear Molecules: These are molecules formed from atoms of the same element. They are also known as molecules of elements. Examples include Oxygen (O₂), Nitrogen (N₂), and Ozone (O₃).
- Heteronuclear Molecules: These are molecules formed from atoms of two or more different elements. They are known as molecules of compounds. Examples include Water (H₂O), Ammonia (NH₃), and Methane (CH₄).
4. Why do atoms combine to form molecules in the first place?
Atoms combine to form molecules primarily to achieve a state of greater stability. Most individual atoms (except for noble gases) have an unstable electron arrangement in their outermost shell. By forming chemical bonds with other atoms, they can share, lose, or gain electrons to achieve a stable electron configuration, often resembling that of the nearest noble gas (known as the octet rule). This process releases energy, resulting in a lower-energy, more stable entity—the molecule.
5. How are atoms, elements, and molecules fundamentally related to each other?
These three terms describe matter at different levels of organisation:
- An atom is the smallest, most fundamental unit of an element.
- An element is a pure substance consisting of only one type of atom (e.g., pure iron is made only of iron atoms).
- A molecule is formed when two or more atoms (either of the same element or different elements) are chemically bonded together. It is the smallest unit of a substance that exhibits the properties of that substance.
6. Can we see a single molecule? If not, how do scientists study them?
No, it is impossible to see a single molecule with the naked eye or even with a standard light microscope. This is because molecules are smaller than the wavelength of visible light. However, scientists can 'see' or map them using highly advanced instruments like the Scanning Tunnelling Microscope (STM) or the Atomic Force Microscope (AFM). These tools don't use light but instead use a fine-tipped probe to scan the surface of a material, allowing them to detect the positions of individual atoms and molecules and create a visual representation.
7. What determines the properties of a substance: its atoms or its molecular structure?
While the constituent atoms are the building blocks, it is the molecular structure—the specific arrangement and bonding of those atoms—that primarily determines the physical and chemical properties of a substance. For example, diamond and graphite are both made purely of carbon atoms. However, because their atoms are arranged in different three-dimensional structures, diamond is extremely hard and transparent, while graphite is soft, black, and slippery. This demonstrates that the arrangement of atoms in a molecule is crucial to its function and properties.
