molecule | Definition, Examples, Structures, & Facts | thetutee
Introduction
A molecule is a combination of two or more atoms that make up the smallest recognizable unit into which a pure material may be split while retaining its makeup and chemical characteristics. Until the parts consisting of single molecules are reached, dividing a sample of a substance into progressively smaller parts creates no change in its composition or chemical characteristics. Further subdivision of the material produces tiny portions that are generally different in composition from the original substance and always different in chemical characteristics. The chemical bonds that keep the atoms in the molecule together are broken in this step of breakage.
Characteristics of Molecules
Atoms are made up of a single positive-charged nucleus surrounded by a cloud of negatively charged electrons. The electron particles interact with each other and with the nuclei as atoms approach each other closely. If the overall energy of the system is reduced as a result of this interaction, the atoms link together to create a molecule. A molecule is thus a collection of atoms held together by valence forces from a structural standpoint. Diatomic molecules are made up of two chemically linked atoms. A homonuclear diatomic molecule is made up of two similar atoms, as in the oxygen molecule (O2), whereas a heteronuclear diatomic molecule is made up of two distinct atoms, as in the carbon monoxide molecule (CO). Polyatomic molecules, such as carbon dioxide (CO2) and water, are molecules with more than two atoms (H2O). Hundreds of molecules make up polymer molecules.
Molecular Bonding
The number of atoms that can be joined together to create molecules has a predetermined ratio; for example, every water molecule has two hydrogen atoms and one oxygen atom. Chemical compounds are distinguished from solutions and other mechanical mixes by this property. In mechanical combinations, hydrogen and oxygen may be present in any arbitrary quantities, but when ignited, they will only combine in certain proportions to produce the chemical complex water (H2O). Two atoms of hydrogen may chemically join with one atom of oxygen to produce a water molecule, whereas two atoms of hydrogen can chemically bond with two atoms of oxygen to form a hydrogen peroxide molecule (H2O2).
Furthermore, atoms can join together in the same amounts to produce distinct compounds. Isomers are molecules that differ solely in the arrangement of their atoms within the molecule. Ethyl alcohol (CH3CH2OH) and methyl ether (CH3OCH3), for example, both include one, two, and six oxygen, carbon, and hydrogen atoms, but these atoms are connected in different ways.
Determining Molecular Structure
Different molecular units do not make up all compounds. For example, sodium chloride (ordinary table salt) is made up of sodium ions and chloride ions organized in a lattice, with each sodium ion surrounded by six equidistant chlorine ions and each chloride ion surrounded by six equidistant sodium ions. The forces exerted on any sodium ion and any chlorine ion close to it are equivalent. As a result, there is no unique aggregation that can be identified as a sodium chloride molecule. As a result, the idea of a chemical molecule has no meaning in sodium chloride and other substances of a similar nature. As a result, the formula for such a compound is written as the atoms' simplest ratio, known as a formula unit—in the instance of sodium chloride, NaCl.
Covalent bonds, or shared electron pairs, hold molecules together. These bonds are directed, which means the atoms take certain orientations relative to one another to increase bond strength. As a result, each molecule's structure, or spatial arrangement of its atoms, is defined and rather rigid. Valence is a concept in structural chemistry that describes how atoms combine in certain ratios and how this is connected to bond orientations and lengths. Molecule attributes are linked to their structures; for example, the water molecule is bent structurally and so has a dipole moment, whereas the carbon dioxide molecule is straight and has none.
Microwave vibration-rotation spectra or neutron diffraction are used to determine the nuclear positions of a molecule. X-ray diffraction investigations may be used to study the electron cloud surrounding the nuclei of a molecule. Electron spin resonance and nuclear magnetic resonance methods can be used to gather more information. Advances in electron microscopy have allowed for the creation of visual representations of individual molecules and atoms. The Schrödinger equation (a quantum mechanical equation for the transport of electrons in the field of nuclei) is used to calculate the molecular structure in theory. Bond lengths and bond angles in a molecular structure are those with the lowest molecular energy. The numerical solution of the Schrödinger equation to determine structures has evolved into a highly developed procedure requiring the use of computers and supercomputers.
Polar and Non-polar Molecules
A molecule's negative charge equals its positive charge if it has no net electrical charge. The forces experienced by such molecules are determined by the arrangement of positive and negative charges in space. The molecule is considered to be nonpolar if the arrangement is spherically symmetric. The molecule has a dipole moment (i.e., a quantifiable propensity to rotate in an electric or magnetic field) if there is an excess of positive charge on one end and an excess of negative charge on the other, and is hence referred to as polar. When polar molecules have the freedom to spin, they gravitate toward orientations that produce attractive forces.
Nonpolar compounds are lipophilic (love lipids), whereas polar substances are hydrophilic (love water). Because they dissolve in the hydrophobic, nonpolar component of the lipid bilayer, lipid-soluble, nonpolar compounds flow easily across a cell membrane. The nonpolar lipid bilayer of cell membranes is permeable to water (a polar molecule), but it is impenetrable to many other polar molecules, such as charged ions or those with numerous polar side chains. Specific transport methods allow polar compounds to travel across lipid membranes.
Molecular Weight
A molecule's molecular weight is the sum of the atomic weights of its constituent atoms. One mole is defined as M grams of a material with a molecular weight of M. For all substances, the number of molecules in one mole is the same; this quantity is known as Avogadro's number. Mass spectrometry and approaches based on thermodynamics or kinetic transport phenomena can be used to calculate molecular weights.
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