molecules

(noun)

A molecule is an electrically neutral group of two or more atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their lack of electrical charge. However, in quantum physics, organic chemistry, and biochemistry, the term molecule is often used less strictly, also being applied to polyatomic ions.

Related Terms

Examples of molecules in the following topics:

  • Homonuclear Diatomic Molecules

    • Diatomic molecules are composed of only two atoms, of either the same or different chemical elements.
    • Common diatomic molecules include hydrogen (H2), nitrogen (N2), oxygen (O2), and carbon monoxide (CO).
    • All diatomic molecules are linear, which is the simplest spatial arrangement of atoms.
    • Translational energies (the molecule moving from point A to point B)
    • A space-filling model of the homonuclear diatomic molecule nitrogen.

  • Molecules

    • Most often, the term "molecules" refers to multiple atoms; a molecule may be composed of a single chemical element, as with oxygen (O2), or of multiple elements, such as water (H2O).
    • Most molecules are too small to be seen with the naked eye.
    • The full elemental composition of a molecule can be precisely represented by its molecular formula, which indicates the exact number of atoms that are in the molecule.
    • Isomers are molecules with the same atoms in different geometric arrangements.
    • Each molecule is a structural isomer of the other.

  • Polyatomic Molecules

    • A polyatomic molecule is a single entity composed of at least three covalently-bonded atoms.
    • Molecules are distinguished from ions by their lack of electrical charge.
    • The science of molecules is called molecular chemistry or molecular physics, depending on the focus.
    • A pure substance is composed of molecules with the same average geometrical structure.
    • Molecules with the same atoms in different arrangements are called isomers.

  • Metabolic Pathways

    • An anabolic pathway requires energy and builds molecules while a catabolic pathway produces energy and breaks down molecules.
    • Another metabolic pathway might build glucose into large carbohydrate molecules for storage.
    • Catabolic pathways involve the degradation of complex molecules into simpler ones, releasing the chemical energy stored in the bonds of those molecules.
    • Anabolic pathways are those that require energy to synthesize larger molecules.
    • Catabolic pathways are those that generate energy by breaking down larger molecules.

  • Outcomes of Glycolysis

    • One glucose molecule produces four ATP, two NADH, and two pyruvate molecules during glycolysis.
    • Glycolysis starts with one molecule of glucose and ends with two pyruvate (pyruvic acid) molecules, a total of four ATP molecules, and two molecules of NADH .
    • Two ATP molecules were used in the first half of the pathway to prepare the six-carbon ring for cleavage, so the cell has a net gain of two ATP molecules and 2 NADH molecules for its use.
    • If the cell cannot catabolize the pyruvate molecules further (via the citric acid cycle or Krebs cycle), it will harvest only two ATP molecules from one molecule of glucose.
    • In this situation, the entire glycolysis pathway will continue to proceed, but only two ATP molecules will be made in the second half (instead of the usual four ATP molecules).

  • Water’s Solvent Properties

    • Water's polarity makes it an excellent solvent for other polar molecules and ions.
    • A polar molecule with partially-positive and negative charges, it readily dissolves ions and polar molecules.
    • The charges associated with these molecules form hydrogen bonds with water, surrounding the particle with water molecules.
    • Water is a poor solvent, however, for hydrophobic molecules such as lipids.
    • Nonpolar molecules experience hydrophobic interactions in water: the water changes its hydrogen bonding patterns around the hydrophobic molecules to produce a cage-like structure called a clathrate.

  • Riboswitches

    • Riboswitches are naturally occurring RNA molecules that can regulate gene expression.
    • Riboswitches are specific components of an mRNA molecule that regulates gene expression.
    • The riboswitch is a part of an mRNA molecule that can bind and target small target molecules.
    • An mRNA molecule may contain a riboswitch that directly regulates its own expression.
    • Hence, the existence of RNA molecules provide evidence to the RNA world hypothesis that RNA molecules were the original molecules, and that proteins developed later in evolution.

  • Molecules in Biological Membranes

  • More complex organic molecules and life

  • Dipole-Dipole Force

    • Molecules that contain dipoles are called polar molecules and are very abundant in nature.
    • A dipole is a molecule that has split charge.
    • The negatively charged oxygen atom of one molecule attracts the positively charged hydrogen of another molecule.
    • Attractions between polar molecules vary.
    • Choose a pair of molecules from the drop-down menu and "pull" on the star to separate the molecules.