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Chemistry is the scientific study of the properties and behavior of matter. It is a natural science that covers the elements that make up matter to the compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they undergo during a reaction with other substances. Chemists often find it useful to look at matter differently than physicists. The starting point is different. The two starting point are consistent but emphasize different things. This article attempts to describe things as they are presented in college chemistry courses.

The Nature of Matter
Matter is anything that has mass and occupies volume (has weight and takes up space).

Matter is composed of small particles called atoms.

Atoms are made up of smaller particles called subatomic particles. The subatomic particles considered important in the understanding of chemistry are the electron (discovered -1897), the proton (1896), and the neutron (1932). In physics, only the electron is considered an elementary particle. Protons and neutrons are composed of other smaller subatomic particles. (In nuclear chemistry, the positron is often included as a elementary particle to be studied.)

The particles are arranged with a nucleus composed of protons and neutrons surrounded by the electrons moving in orbitals.

The number of protons in the nucleus defines the kind of atom. The same kind of atom can exist with different numbers of neurons on the nucleus. Such atoms are called isotopes of each other. There are limits on the number of protons and neutrons that can exist in atoms, described by the band of stability.

The Classification of Matter
Matter can be identified as an element, a compound, or a mixture.

An element is a pure substance composed of only one kind of atom.

A compound is a pure substance composed of more than one kind of atom. A compound can be either ionic or molecular.

A mixture is composed of more than one kind of element and/or compound.

Matter can be described with both physical properties and chemical properties.

Physical properties are characteristics that describe matter. They include characteristics such as size, shape, color, and mass. These characteristics can be observed or measured without changing the identity of the matter in question.

Chemical properties are characteristics that describe how matter changes its chemical structure or composition. An example of a chemical property is flammability—a material’s ability to burn—because burning (also known as combustion) changes the chemical composition of a material. The observation of chemical properties involves a chemical change of the matter in question, resulting in matter with a different identity and different physical and chemical properties.

States of Matter
There are three basic states of matter: Solids, Liquids, and Gases.

A solid is in a state in which matter maintains a fixed volume and shape

A liquid is in a state in which matter maintains a fixed volume but adapts to the shape of its container.

A gas is the state in which matter expands to occupy whatever volume is available.

These three states are the three fundamental states of matter in chemistry, but they do not include all possible conditions in which matter is found. Additional states of matter have been described and named. There is no unambiguous definition of a state of matter; ultimately the definitions of the states are arbitrarily defined. However, there is another state, which is often cited as the "fourth sate of matter" in the field of physics. That is a plasma.

In physics, a plasma consists of a gas of ions, in which there are free electrons along with the atoms or molecules from which they came. In a high energy plasma, all the electrons are stripped, and it consists of atomic nuclei swimming in a sea of electrons.

The traditional definition of a plasma in chemistry was "ions in the gaseous state", and did not require a separate state of matter. Such a plasma can be produced by heating ionic salts (such as NaCl) well above their melting point. The study of the chemistry of plasmas may be referred to as gas-phase ion chemistry.

There are two "states of matter" that are very important to chemistry. They are the supercritical fluids and materials in the plastic state.

Th critical state is a state in which the liquid and vapor (gas) states have the same density. A super critical fluid has a temperature above the critical temperature and pressure.

The plastic state is best known for polymers. A polymer is a substance or material consisting of very large molecules, or macromolecules, composed of many repeating sub-units. When a polymer is cooled very rapidly, it tends to form a brittle amorphous solid called a glass. When such a mateial is heated, it reach a point called the glass transition temperature when it softens, and can be deformed without breaking. This may be called the plastic state. If the polymer is cooled very slowly, it will form a crystalline solid.

Matter word list
Gas  A gas is a substance which takes the shape of its container and expands to completely fill its container.

Ideal Gas Ideal gasses refer to the behavior which gasses approach as the pressure nears zero. This behavior is described mathematically by the ideal gas law. Although no gas behaves exactly as an ideal gas, many substances come very close to ideal behavior at atmospheric pressure and most behave ideally at very low pressures.

Real Gas Most molecules attract one another until they come very close together, when they become repulsive (i.e., they bounce off each other). The attraction is due to the electrostatic interactions between the two molecules. The repulsion between molecules at very close distances is due to the repulsion between the nuclei of the two molecules. These forces give rise to relationships between the pressure, temperature, volume and quantity of a substance, which do not exactly obey the ideal gas law. Gasses under physical conditions that give non-ideal behavior are called real gasses.

Supercritical Fluids At a given temperature, a gas can be compressed until it starts to condense into a liquid displaying a clear boundary between the liquid at the bottom of the container and the gas. Above a certain temperature, called the critical temperature, a gas can be compressed without ever observing a clear liquid - gas boundary. Gasses in this state are called super-critical fluids. It is sometimes described as a gas with the density of a liquid.

Plasma Ions in the gaseous state.

Liquid A liquid is a substance which takes the shape of its container and has a fixed volume at a given temperature and pressure. Suspensions, colloids, liquid crystals and viscoelastic materials have properties intermediate between those of a liquid and a solid.

Suspension A material in which small solid particles are mixed uniformly with a liquid. A suspension behaves as a liquid.

(Liquid) Solution A material in which other materials are dissolved and mixed uniformly on the molecular scale with a liquid. Such a solution behaves as a liquid.

Colloid A colloid is a material which appears to be liquid but actually is a suspension of particles too small to observe with a microscope but bigger than normal molecules.

Liquid Crystal In crystals, the atoms are arranged in an ordered repeating pattern. Inliquids there is no ordered pattern. In liquid crystals there is order in one or two directions while there is no order in the other directions. This gives a number of unique properties such as optical properties that can be turned off and on to make liquid crystal displays for watches and computers. There will also be changes in the viscosity of a substance when it reaches a liquid crystal phase.

Solid Solid state materials are characterized by having a fixed volume and shape. Crystals, glasses and elastomers are all types of solids.

Crystal Crystals are solid state materials in which the atoms are arranged in an ordered repeating pattern. Many molecules will form crystals in which the original molecules are still distinguishable only stacked neatly. Organic compounds often form these molecular crystals. In other crystals, such as metal alloys, there is a repeating pattern but no distinguishable molecular units.

Solid Solution A solid solution is a solid-state solution of one or more solutes in a another material, called the solvent. Such a mixture is considered a solution rather than a compound when the crystal structure of the solvent remains unchanged by addition of the solutes, and when the mixture remains in a single homogeneous phase. This often happens when the two elements (generally metals) involved are close together on the periodic table; conversely, a chemical compound is generally a result of non-proximity of the two metals involved on the periodic table.

Viscoelastic Some compounds such as natural rubber appear to be solid when they are stretched, bent or set on a table top. However, over a period of time these materials will slowly deform to take the shape of the container. Substances, which act as solid onshort time scales and act as liquids on long time scales are, called viscoelastic materials.

Glass Glasses are amorphous solids, meaning that the atoms are not arranged in any repeating pattern. When a liquid is cooled very slowly it tends to form a crystal, while cooling quickly can result in amorphous phases. Glasses are distinguished from elastomers by being brittle.

Elastomer An elastomer is an amorphous solid which can be deformed without breaking.

Plastic State Pertaining to a material that can deform permanently without rupturing.

-->Chemistry is the scientific study of the properties and behavior of matter. It is a natural science that covers the elements that make up matter to the compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they undergo during a reaction with other substances. Chemists often find it useful to look at matter differently than physicists. The starting point is different. The two starting point are consistent but emphasize different things. This article attempts to describe things as they are presented in college chemistry courses.

The Nature of Matter
Matter is anything that has mass and occupies volume (has weight and takes up space).

Matter is composed of small particles called atoms.

Atoms are made up of smaller particles called subatomic particles. The subatomic particles considered important  in the understanding of chemistry are the electron (discovered -1897), the proton (1896), and the neutron (1932). In physics, only the electron is considered an elementary particle. Protons and neutrons are composed of other smaller subatomic particles. (In nuclear chemistry, the positron is often included as a elementary particle to be studied.)

The particles are arranged with a nucleus composed of protons and neutrons surrounded by the electrons moving in orbitals.

The number of protons in the nucleus defines the kind of atom. The same kind of atom can exist with different numbers of neurons on the nucleus. Such atoms are called isotopes of each other. There are limits on the number of protons and neutrons that can exist in atoms, described by the band of stability.

The Classification of Matter
Matter can be identified as an element, a compound, or a mixture.

An element is a pure substance composed of only one kind of atom.

A compound is a pure substance composed of more than one kind of atom. A compound can be either ionic or molecular.

A mixture is composed of more than one kind of element and/or compound.

Matter can be described with both physical properties and chemical properties.

Physical properties are characteristics that describe matter. They include characteristics such as size, shape, color, and mass. These characteristics can be observed or measured without changing the identity of the matter in question.

Chemical properties are characteristics that describe how matter changes its chemical structure or composition. An example of a chemical property is flammability—a material’s ability to burn—because burning (also known as combustion) changes the chemical composition of a material. The observation of chemical properties involves a chemical change of the matter in question, resulting in matter with a different identity and different physical and chemical properties.

States of Matter
There are three basic states of matter: Solids, Liquids, and Gases.

A solid is in a state in which matter maintains a fixed volume and shape

A liquid is in a state in which matter maintains a fixed volume but adapts to the shape of its container.

A gas is the state in which matter expands to occupy whatever volume is available.

These three states are the three fundamental states of matter in chemistry, but they do not include all possible conditions in which matter is found. Additional states of matter have been described and named. There is no unambiguous definition of a state of matter;  ultimately the definitions of the states are arbitrarily defined. However, there is another state, which is often cited as the "fourth sate of matter" in the field of physics. That is a plasma.

In physics, a plasma consists of a gas of ions, in which there are free electrons along with the atoms or molecules from which they came. In a high energy plasma, all the electrons are stripped, and it consists of atomic nuclei swimming in a sea of electrons.

The traditional definition of a plasma in chemistry was "ions in the gaseous state", and did not require a separate state of matter. Such a plasma can be produced by heating ionic salts (such as NaCl) well above their melting point. The study of the chemistry of plasmas may be referred to as gas-phase ion chemistry.

There are two "states of matter" that are very important to chemistry. They are the supercritical fluids and materials in the plastic state.

Th critical state is a state in which the liquid and vapor (gas) states have the same density. A super critical fluid has a temperature above the critical temperature and pressure.

The plastic state is best known for polymers. A polymer is a substance or material consisting of very large molecules, or macromolecules, composed of many repeating sub-units. When a polymer is cooled very rapidly, it tends to form a brittle amorphous solid called a glass. When such a mateial is heated, it reach a point called the glass transition temperature when it softens, and can be deformed without breaking. This may be called the plastic state. If the polymer is cooled very slowly, it will form a crystalline solid.

Matter word list
Gas   A gas is a substance which takes the shape of its container and expands to completely fill its container.

Ideal Gas Ideal gasses refer to the behavior which gasses approach as the pressure nears zero. This behavior is described mathematically by the ideal gas law. Although no gas behaves exactly as an ideal gas, many substances come very close to ideal behavior at atmospheric pressure and most behave ideally at very low pressures.

Real Gas Most molecules attract one another until they come very close together, when they become repulsive (i.e., they bounce off each other). The attraction is due to the electrostatic interactions between the two molecules. The repulsion between molecules at very close distances is due to the repulsion between the nuclei of the two molecules. These forces give rise to relationships between the pressure, temperature, volume and quantity of a substance, which do not exactly obey the ideal gas law. Gasses under physical conditions that give non-ideal behavior are called real gasses.

Supercritical Fluids At a given temperature, a gas can be compressed until it starts to condense into a liquid displaying a clear boundary between the liquid at the bottom of the container and the gas. Above a certain temperature, called the critical temperature, a gas can be compressed without ever observing a clear liquid - gas boundary. Gasses in this state are called super-critical fluids. It is sometimes described as a gas with the density of a liquid.

Plasma  Ions in the gaseous state.

Liquid  A liquid is a substance which takes the shape of its container and has a fixed volume at a given temperature and pressure. Suspensions, colloids, liquid crystals and viscoelastic materials have properties intermediate between those of a liquid and a solid.

Suspension A material in which small solid particles are mixed uniformly with a liquid. A suspension behaves as a liquid.

(Liquid) Solution A material in which other materials are dissolved and mixed uniformly on the molecular scale with a liquid. Such a solution behaves as a liquid.

Colloid A colloid is a material which appears to be liquid but actually is a suspension of particles too small to observe with a microscope but bigger than normal molecules.

Liquid Crystal In crystals, the atoms are arranged in an ordered repeating pattern. Inliquids there is no ordered pattern. In liquid crystals there is order in one or two directions while there is no order in the other directions. This gives a number of unique properties such as optical properties that can be turned off and on to make liquid crystal displays for watches and computers. There will also be changes in the viscosity of a substance when it reaches a liquid crystal phase.

Solid Solid state materials are characterized by having a fixed volume and shape. Crystals, glasses and elastomers are all types of solids.

Crystal Crystals are solid state materials in which the atoms are arranged in an ordered repeating pattern. Many molecules will form crystals in which the original molecules are still distinguishable only stacked neatly. Organic compounds often form these molecular crystals. In other crystals, such as metal alloys, there is a repeating pattern but no distinguishable molecular units.

Solid Solution A solid solution is a solid-state solution of one or more solutes in a another material, called the solvent. Such a mixture is considered a solution rather than a compound when the crystal structure of the solvent remains unchanged by addition of the solutes, and when the mixture remains in a single homogeneous phase. This often happens when the two elements (generally metals) involved are close together on the periodic table; conversely, a chemical compound is generally a result of non-proximity of the two metals involved on the periodic table.

Viscoelastic  Some compounds such as natural rubber appear to be solid when they are stretched, bent or set on a table top. However, over a period of time these materials will slowly deform to take the shape of the container. Substances, which act as solid onshort time scales and act as liquids on long time scales are, called viscoelastic materials.

Glass Glasses are amorphous solids, meaning that the atoms are not arranged in any repeating pattern. When a liquid is cooled very slowly it tends to form a crystal, while cooling quickly can result in amorphous phases. Glasses are distinguished from elastomers by being brittle.

Elastomer An elastomer is an amorphous solid which can be deformed without breaking.

Plastic State  Pertaining to a material that can deform permanently without rupturing.