What Are The Energy Stores In Molecules?

Molecules contain various forms of energy that allow them to participate in chemical reactions and provide energy for biological processes. The main energy stores found within molecules include chemical energy, nuclear energy, electromagnetic energy, elastic potential energy, mechanical energy, thermal energy, sound energy, and light energy. This article will examine each of these key energy stores and discuss their roles in molecules.

Chemical Energy

Chemical energy is the potential energy stored in the bonds between atoms that make up molecules. It is the energy released when chemical bonds are formed and absorbed when chemical bonds are broken. Some examples of molecules that store chemical energy include:

a diagram showing chemical energy stored in the bonds of a glucose molecule.

  • Carbohydrates like glucose and starch – The energy in the bonds between carbon, hydrogen and oxygen atoms is released during cellular respiration to power biological processes.

  • Fats and oils – The energy stored in the bonds between fatty acid chains and glycerol provide concentrated energy storage for organisms.

  • Proteins – The peptide bonds linking amino acids contain energy that supports protein structure and function.

  • ATP – The phosphate bonds in this energy carrier molecule can release energy to power biochemical reactions when broken via hydrolysis.

In summary, molecules like carbohydrates, fats, proteins and ATP store large amounts of chemical potential energy in their atomic bonds that can be harnessed to perform work.

Nuclear Energy

Nuclear energy is the energy stored in the nucleus of an atom. Atoms are made up of protons, neutrons, and electrons. The protons and neutrons are densely packed together in the nucleus. Nuclear energy comes from the forces that hold the nucleus together. There are two types of nuclear energy:

1. Nuclear binding energy – This is energy that holds the protons and neutrons together in the atomic nucleus. The binding energy increases as the number of protons and neutrons increases in the nucleus, reaching a peak at iron. Nuclei larger than iron have less binding energy per nucleon. Nuclear fusion reactions (combining lighter nuclei) release binding energy, while nuclear fission reactions (splitting heavier nuclei) absorb binding energy.

2. Nuclear potential energy – This is energy stored in the nuclear force between nucleons. The nuclear force is attractive at short distances but repulsive at longer distances. Bringing nucleons closer together decreases potential energy, while forcing them apart increases it. Nuclear potential energy allows energy to be released in nuclear decay, where the nucleus spontaneously emits particles and energy.

Examples of nuclear energy in molecules include:

  • The bond between protons and neutrons in atomic nuclei like uranium-235.
  • Energy released in nuclear fission of uranium atoms in nuclear power plants.
  • Energy released in nuclear fusion of hydrogen atoms in the sun.
  • Decay of radioactive elements like radium and radon.

In summary, nuclear energy arises from forces between nucleons in an atomic nucleus. It is harnessed for power generation in nuclear fission and fusion reactions.

Electromagnetic Energy

Electromagnetic energy is energy stored in the electromagnetic fields of atoms and molecules. This includes several types of energy:

  • Electric potential energy – Energy stored in the electric field of charged particles like protons and electrons. For example, the buildup of charge separation across cell membranes stores electric potential energy.
  • Magnetic potential energy – Energy stored in the magnetic field generated by the spin and orbital motion of electrons. This energy stabilizes the structure of atoms and molecules.
  • Photons – Light is a form of electromagnetic radiation that carries energy in discrete packets called photons. Excited electrons store energy in photons when relaxing to lower energy states.

Electromagnetic energy is important for many molecular processes like chemical reactions, light emission, cell metabolism, and more. It provides one way for energy to be stored within molecules.

Elastic Potential Energy

Elastic potential energy is stored in the bonds between atoms when they are stretched or compressed. Molecules can store energy when the chemical bonds between atoms are distorted. This stored energy can later be released when the bonds return to their original shape.

A common example of elastic potential energy in molecules is found in rubber bands. The polymer chains that make up rubber are coiled and tangled when relaxed. But when you stretch a rubber band, the polymer chains are forced to straighten out, which requires energy. The extended rubber band can now spring back to its original shape, releasing the stored elastic potential energy.

Similarly, many proteins and enzymes store elastic potential energy in their molecular structure. The peptide bonds between amino acids can be twisted and distorted. When external stresses are removed, the protein returns to its lowest energy shape, releasing the stored elastic energy. Molecular springs like polysaccharide chains in plant cell walls also exhibit elastic potential energy.

Mechanical Energy

Mechanical energy is the energy stored in objects by tension or motion. On a molecular level, mechanical energy can be stored in the bonds between atoms through deformation and stretching.

For example, rubber and springs are able to store mechanical energy when they are stretched or compressed. This is because the polymer chains that make up rubber and the metal coils in springs are elongated or compressed. When released, these molecules snap back to their resting positions, releasing the stored mechanical energy.

Another example is ATP, or adenosine triphosphate, which is the main energy carrier molecule found in cells. ATP contains high-energy phosphate bonds that can release energy when broken through a process called hydrolysis. The energy released allows ATP to fuel cellular processes and muscle contraction. So the mechanical energy is stored in the strained high-energy bonds until they are broken to release the energy.

Thermal Energy

Thermal energy refers to the internal energy present in molecules due to their temperature. Molecules are constantly vibrating and moving, and the higher their temperature, the faster their motions. This microscopic kinetic energy is what we sense macroscopically as heat. The total thermal energy in a substance depends on the number of molecules present and their average kinetic energy.

Molecules can store thermal energy in different ways. In gases, the main form of energy storage is the kinetic energy of molecular translation and rotation. In liquids and solids, molecules also possess vibrational energy in their chemical bonds. The more ways a molecule can move, the more thermal energy it can possess at a given temperature.

Some examples of thermal energy storage in molecules:

  • Nitrogen gas molecules store energy through translation and rotation.
  • Water molecules in liquid form also vibrate and bend their chemical bonds.
  • The complex molecules in gasoline possess many vibrational modes that can store thermal energy.
  • Metals contain atoms that vibrate against each other in crystal structures.

In summary, the thermal energy stored in molecules manifests as random microscopic motion. More complex molecules with more degrees of freedom can store more thermal energy at a given temperature.

Sound Energy

Molecules can store sound energy through vibrations. As sound waves travel through a medium like air, the molecules in the air vibrate back and forth. The kinetic energy of these vibrations is the sound energy being stored in the molecules. The greater the amplitude of the vibrations, the more sound energy is stored.

Some examples of molecules storing sound energy include:

  • The molecules of air vibrating as music plays from speakers
  • The molecules of water vibrating from underwater noises like sonar pings
  • The molecules in our eardrums vibrating as they receive and transduce soundwaves into nerve signals

In each of these cases, the kinetic energy of the molecular vibrations represents the sound energy being stored momentarily as the sound waves pass through. The molecules return to their resting positions once the sound has traveled through.

Light Energy

Light energy is stored in molecules through electronic excitation. When a molecule absorbs a photon of light, one of its electrons is promoted to a higher energy orbital. This stores the energy from the photon in the excited electronic state of the molecule.

A common example is the storage of light energy in retinal, the light-sensitive molecule in your eyes. Retinal contains a network of double bonds that have pie electrons that can be excited by visible light photons. This electronic excitation triggers a signal to your visual cortex, allowing you to see.

Another example is chlorophyll, the key light-absorbing pigment in plants. Chlorophyll molecules contain a network of conjugated double bonds similar to retinal. When chlorophyll absorbs sunlight, the energy excites its electrons into a higher energy state. This excited state then drives photosynthesis and the storage of energy in glucose molecules.

In summary, light energy is commonly stored in molecules through electronic excitation, such as in retinal for vision or chlorophyll for photosynthesis. The energy is stored in higher energy orbitals until the molecule relaxes back down by dissipating the energy.


In summary, there are various forms of energy that can be stored in molecules. Chemical energy stored in the bonds between atoms is a key source of potential energy in molecules. Nuclear energy stored in the nuclei of atoms through binding forces between protons and neutrons is the most concentrated form. Electromagnetic energy stored in the interactions between charged particles and magnetic fields enables many molecular processes. Elastic potential energy stored through molecular shape changes allows for mechanical motions. Thermal energy from molecular motion provides heat. Sound energy from vibration propagates through mediums. Light energy from oscillating electric/magnetic fields illuminates. Understanding the different molecular energy stores and how they can interconvert enables insights into many natural phenomena and technologies.

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