Matter is the material substance of the observable universe that possesses inertia and gravitational mass. It is composed of elementary particles called quarks and leptons, which combine to form protons, neutrons, and electrons, further creating atoms and molecules. Clusters are a state of matter consisting of small groups of atoms, molecules, or ions bound together by various forces. These forces include van der Waals forces, ionic forces, covalent bonds, and metallic bonds. The properties of clusters can differ from those of the corresponding bulk material, offering insights into how the properties of matter evolve from the atomic level to the macroscopic scale.

What are atoms and molecules?

An atom is the basic building block of matter and chemistry. It cannot be divided into smaller parts through chemical processes. An atom consists of a nucleus containing protons and neutrons, surrounded by electrons. A molecule is a group of two or more atoms that form the smallest identifiable unit of a pure substance while retaining its composition and chemical properties. Molecules are held together by chemical bonds, which involve the sharing or exchange of electrons between atoms. Clusters combine bulk and molecular matter properties. Metallic clusters can cause molecules to dissociate. The chemical properties of clusters can be influenced by light, leading to reactions such as molecular dissociation or electron detachment.

How do solids, liquids, and gases differ?

Gases, liquids, and solids differ in their structure and properties. Gases lack definite size and shape, filling any closed container. In gases, molecules are independent, occasionally colliding. Liquids have a definite volume but adapt their shape to their container. They possess high density and partial order, with molecules remaining in constant contact. Solids have a definite size and shape and resist forces. They form when atoms decrease in energy and take on a three-dimensional structure. Solids are either crystalline, amorphous, or quasicrystalline. Crystalline solids have ordered atomic arrangements, while amorphous solids lack a definite lattice pattern.

What is the difference between a physical change and a chemical change?

A physical change alters the physical properties of a substance but not its chemical identity. Changes of state, such as melting ice or evaporating water, are examples of physical changes. The substance remains the same compound, like H2O, regardless of its physical state. A chemical reaction involves the rearrangement of atoms to create new substances. For instance, sodium metal (Na) reacts with water (H2O) to form molecular hydrogen (H2) and sodium hydroxide (NaOH), indicating a chemical change has occurred. Redox reactions , where electrons are transferred between substances, also exemplify chemical changes.

How does energy relate to changes in matter?

Energy is the capacity to do work, and matter can store energy as potential energy. Energy changes in matter occur at the microscopic level through increased molecular motion, such as translational kinetic energy in gas molecules, which is proportional to temperature. Molecules can rotate, atoms can vibrate, and energy can be stored in chemical bonds. When atoms or molecules combine, there's a change in potential energy and a release of kinetic energy. For example, the energy released during methane combustion occurs because the chemical bonds in the products are stronger than in the reactants. Clusters, which bridge molecular and bulk matter, demonstrate how energy relates to changes in matter. Clusters of iron atoms can cause hydrogen molecules to dissociate into hydrogen atoms. The chemical properties of clusters are influenced by light; light can break apart molecules captured within a cluster.

How do chemistry and physics work together to explain how the world around us behaves?

Chemistry and physics intertwine to explain the world's behavior by studying matter, energy, and their interactions. Physics provides the fundamental laws governing the motion, energy, and forces that dictate how matter behaves at macroscopic and submicroscopic levels. Chemistry uses these laws to explore the structure, properties, and reactions of substances, focusing on atoms and molecules. For example, physics explains how atoms bond through electromagnetic forces, while chemistry details how these bonds form diverse molecules with unique properties. Thermodynamics, a principle in physical chemistry, applies physical laws to predict chemical reaction behaviors, conserving energy while increasing entropy, or disorder. Together, these disciplines provide a comprehensive understanding of the universe.

cluster

Introduction
Comparison with other forms of matter
- Comparison with bulk matter
- Comparison with molecules
Methods of study
- Preparation of clusters
- Ionization and sorting of clusters
- Computer simulation of cluster behaviour
Structure and properties
- Structure
  - Clusters with icosahedral structures
  - Clusters of simple metal atoms
  - Network structures
- Physical properties
  - Liquid and solid phases
  - Electric, magnetic, and optical properties
- Chemical properties

References & Edit History Related Topics

Images

Figure 1: The four stable geometric structures of the seven-atom cluster of argon, in order of increasing energy: (A) A pentagonal bipyramid. (B) A regular octahedron with one face capped by the seventh atom. (C) A regular tetrahedron with three of its faces capped by other atoms. (D) A trigonal bipyramid with two of its faces capped by other atoms; although this has the highest energy of the four structures, it is very close in energy to the tricapped tetrahedron.

Figure 2: The four lowest-energy structures of the 13-atom cluster of argon.

Figure 4: The structure of C60, buckminsterfullerene.

cluster

chemistry and physics

Written by

R. Stephen Berry

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History

Top Questions

What is matter?
Matter is the material substance of the observable universe that possesses inertia and gravitational mass. It is composed of elementary particles called quarks and leptons, which combine to form protons, neutrons, and electrons, further creating atoms and molecules.

Clusters are a state of matter consisting of small groups of atoms, molecules, or ions bound together by various forces. These forces include van der Waals forces, ionic forces, covalent bonds, and metallic bonds. The properties of clusters can differ from those of the corresponding bulk material, offering insights into how the properties of matter evolve from the atomic level to the macroscopic scale.
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2. matter
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What are atoms and molecules?
An atom is the basic building block of matter and chemistry. It cannot be divided into smaller parts through chemical processes. An atom consists of a nucleus containing protons and neutrons, surrounded by electrons.

A molecule is a group of two or more atoms that form the smallest identifiable unit of a pure substance while retaining its composition and chemical properties. Molecules are held together by chemical bonds, which involve the sharing or exchange of electrons between atoms.

Clusters combine bulk and molecular matter properties. Metallic clusters can cause molecules to dissociate. The chemical properties of clusters can be influenced by light, leading to reactions such as molecular dissociation or electron detachment.
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How do solids, liquids, and gases differ?
Gases, liquids, and solids differ in their structure and properties. Gases lack definite size and shape, filling any closed container. In gases, molecules are independent, occasionally colliding.

Liquids have a definite volume but adapt their shape to their container. They possess high density and partial order, with molecules remaining in constant contact.

Solids have a definite size and shape and resist forces. They form when atoms decrease in energy and take on a three-dimensional structure. Solids are either crystalline, amorphous, or quasicrystalline. Crystalline solids have ordered atomic arrangements, while amorphous solids lack a definite lattice pattern.
5 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What is the difference between a physical change and a chemical change?
A physical change alters the physical properties of a substance but not its chemical identity. Changes of state, such as melting ice or evaporating water, are examples of physical changes. The substance remains the same compound, like H2O, regardless of its physical state.

A chemical reaction involves the rearrangement of atoms to create new substances. For instance, sodium metal (Na) reacts with water (H2O) to form molecular hydrogen (H2) and sodium hydroxide (NaOH), indicating a chemical change has occurred. Redox reactions, where electrons are transferred between substances, also exemplify chemical changes.
6 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How does energy relate to changes in matter?
Energy is the capacity to do work, and matter can store energy as potential energy. Energy changes in matter occur at the microscopic level through increased molecular motion, such as translational kinetic energy in gas molecules, which is proportional to temperature. Molecules can rotate, atoms can vibrate, and energy can be stored in chemical bonds.

When atoms or molecules combine, there's a change in potential energy and a release of kinetic energy. For example, the energy released during methane combustion occurs because the chemical bonds in the products are stronger than in the reactants.

Clusters, which bridge molecular and bulk matter, demonstrate how energy relates to changes in matter. Clusters of iron atoms can cause hydrogen molecules to dissociate into hydrogen atoms. The chemical properties of clusters are influenced by light; light can break apart molecules captured within a cluster.
5 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How do chemistry and physics work together to explain how the world around us behaves?
Chemistry and physics intertwine to explain the world's behavior by studying matter, energy, and their interactions. Physics provides the fundamental laws governing the motion, energy, and forces that dictate how matter behaves at macroscopic and submicroscopic levels. Chemistry uses these laws to explore the structure, properties, and reactions of substances, focusing on atoms and molecules.

For example, physics explains how atoms bond through electromagnetic forces, while chemistry details how these bonds form diverse molecules with unique properties. Thermodynamics, a principle in physical chemistry, applies physical laws to predict chemical reaction behaviors, conserving energy while increasing entropy, or disorder. Together, these disciplines provide a comprehensive understanding of the universe.
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Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

cluster, Atoms and molecules are the smallest forms of matter typically encountered under normal conditions and are in that sense the basic building blocks of the material world. There are phenomena, such as lightning and electric discharges of other kinds, that allow free electrons to be observed, but these are exceptional occurrences. It is of course in its gaseous state that matter is encountered at its atomic or molecular level; in gases each molecule is an independent entity, only occasionally and briefly colliding with another molecule or with a confining wall.

In contrast to the free-molecule character of gases, the condensed phases of matter—as liquids, crystalline solids, and glasses are called—depend for their properties on the constant proximity of all their constituent atoms. The extent to which the identities of the molecular constituents are maintained varies widely in these condensed forms of matter. Weakly bound solids, such as solid carbon dioxide (dry ice), or their liquid counterparts, such as liquid air or liquid nitrogen, are made up of molecules whose properties differ only slightly from the properties of the same molecules in gaseous form; such solids or liquids are simply molecules packed tightly enough to be in constant contact. These are called van der Waals solids or liquids, after Johannes D. van der Waals, the Dutch physicist who described the weak forces that just manage to hold these materials together if they are cold enough. In other solids, like diamond, graphite, silicon, or quartz, the individual atoms retain their identity, but there are no identifiable molecules in their structures. The forces between the constituent atoms are roughly as strong as the forces that hold atoms together in the strongly bound covalent molecules that make up most common substances. Negatively charged electrons act as a “glue” to hold the positively charged nuclei together and are more or less confined to the vicinity of the so-called home-base nuclei with which they are associated; they are not free to roam through the entire solid or liquid. These materials are said to be covalently bound and are electrical insulators. They are best described as neutral atoms held together by covalent bonds and are essentially one giant molecule.

Another kind of bonding found in condensed matter is exhibited by sodium chloride, ordinary table salt, which is composed of positive sodium ions (Na⁺) and negative chloride ions (Cl^-). Such ionic compounds are held together by the mutual attraction of the oppositely charged ions; because of their locations, these attractions are stronger than the repulsions of the ions with like charges. Each ion in an ionic crystal is surrounded by nearest neighbours of opposite charge. The consequence is that the binding energies of ionic compounds are large, comparable to those of strongly bound covalent substances.

Metallic bonding is another type of binding found in condensed matter. Electrons moving between the positive atomic cores (i.e., the nuclei plus inner-shell, tightly bound electrons) form an electron cloud; the attractions between the positive cores and the negative charges that make up the cloud hold metals together. Metals differ from covalently bound insulators in that those electrons responsible for the cohesion of the metals move freely throughout the metal when given the slightest extra energy. For example, under the influence of the electric field produced in a copper wire when its ends are connected to the terminals of a battery, electrons move through the wire from the end connected to the battery’s negative pole toward the end connected to its positive pole. An electric field applied to a metal generates an electric current, but the same electric field applied to a covalent insulator does not (see below Comparison with other forms of matter). The net binding forces between electrons and atomic cores of a metal are comparable in strength to those that hold ionic compounds together.

As mentioned above, liquids constitute a condensed or dense phase of matter, but their atomic arrangement differs from that of solids. In a liquid the constituent atoms are only slightly farther apart than they are in a solid, but that small difference is significant enough to allow the atoms or molecules that constitute a liquid to move around and to assume a full range of geometric configurations. Atoms of the same kind can trade places and can wander through the liquid by the random-walk process called diffusion. In general, materials that can form solids can also form liquids, but some, such as carbon dioxide, can only enter the liquid state under excess pressure. At least one substance, helium, can form a liquid while having no known solid form.

Italian-born physicist Dr. Enrico Fermi draws a diagram at a blackboard with mathematical equations. circa 1950.

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Physics and Natural Law

Materials that form solids and liquids can exhibit another form, one that may be solidlike or liquidlike but that has properties somewhat different from those of the bulk. This is the form of matter consisting of exceedingly small particles that are called clusters. Clusters are aggregates of atoms, molecules, or ions that adhere together under forces like those that bind the atoms, ions, or molecules of bulk matter; because of the manner in which they are prepared, clusters remain as tiny particles at least during the course of an experiment. There are clusters held together by van der Waals forces, by ionic forces, by covalent bonds, and by metallic bonds. Despite the similarity of the forces that bind both clusters and bulk matter, one of the fascinating aspects of clusters is that their properties differ from those of the corresponding bulk material; that characteristic affords the opportunity to learn about the properties of bulk matter by studying how, as the number of constituent particles increases, the properties of clusters evolve into those of bulk matter. For example, a cluster of 20 or 30 atoms typically has a melting point far lower than that of the corresponding bulk. The electrical properties of clusters also differ in some instances from those of the bulk matter: clusters of only a few atoms of mercury are insulators, held together by weak van der Waals forces, but clusters of hundreds of mercury atoms are metallic. One of the puzzles posed by clusters is the question of how properties of small clusters evolve with size into properties of bulk matter.

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