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Heat Transfer: Crash Course Engineering #14

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Thermal Energy Transfer: Conduction, Convection, Radiation

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Thermal Energy Transfer: Conduction, Convection, Radiation

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All things are made up of molecules

When things get heated, they absorb heat energy

With more energy, molecules are able to move faster

When molecules move faster, the temperature rises

Thermal Energy is energy resulting from the motion of particles

It is a form of kinetic energy and is transferred as heat

Thermal Energy Transfer can occur by three methods:

Conduction

Convection

Radiation

Conduction

Conduction is the transfer of thermal energy through direct contact between particles of a substance, without moving the particles to a new location

Usually occurs in solids

When heat is supplied to one end, molecules at that end start to move more quickly

In the process, they bump into their neighbours, transferring the kinetic energy

Convection

Convection is the transfer of thermal energy through movement of particles from one location to another

Usually occur in fluids (liquids and gases)

Example with boiling water:

Water at bottom of pan is heated first

Heated water expands and density decreases

Heated water begins to rise

Cooler water with higher density from the sides of the pan rush down to take its place

The cooler water gets heated and the cycle repeats

We call these Convection Currents

Radiation

Radiation is the emission of energy as waves or particles or rays

Radiation does not require a medium to transfer energy

Radiant energy is either reflected or absorbed by matter

Energy that is absorbed increases the kinetic energy of the object

This increases the temperature of the object

Example ... frying pan on a stove top

Energy is radiated from the heat source and absorbed by the lower surface of the pan

Example ... the sun

Sun radiates energy in form of solar radiation

When this energy reaches Earth, it is absorbed by matter (air, water, land)

Absorbed radiant energy increases kinetic energy of the matter, raising its temperature

The sun is an emitter

It gives out heat

The Earth is an absorber

It takes in the heat

ALBEDO

Colour of the surface

Albedo is the percentage of the incoming solar radiation that it reflects

Albedo of Earth is about 30%

Light-coloured, shiny objects reflect more solar radiation and have a high albedo (ice, snow, sand)

Darker, dull objects absorb more solar radiation and have a low albedo (forests, soils)

Factors Affecting Radiation

Surface Temperature

The higher the surface temperature, the higher the rate of transfer

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Surface Area

The larger the surface area, the higher the rate of transfer

Thermal Energy Transfer in the Atmopshere

Things to Know:

Atmospheric Pressure > the pressure exerted by the mass of air above any point on Earth's surface

Warm air is less dense than cold air

Warmer regions generally have less atmospheric pressure than colder regions

Wind > the movement of air from areas of high pressure to areas of low pressure

The rising and sinking masses of air in convection currents cause changes in atmospheric pressure ... causing wind

Wind Patterns and Coriolis Effect

Moves from WEST to EAST

Closer to equator in colder monthes

Closer to Poles in warmer months

Thermal Energy Transfer in the Hydrosphere

Effect of water on transfer of heat is significant

Earth's climate is effected by phase changes in the water cycle

Water Cycle

Water molecules undergo changes of state (e.g. solid to liquid)

When these changes occur, thermal energy is either released or absorbed

Released from liquid > solid

Absorbed from Liquid > gas

Temp. remains the same between phase changes

Through changes of state is how thermal energy is transferred through the biosphere

Ocean Currents

Main pathways to transfer thermal energy from warmer regions to cooler regions

Global winds push the water, driving the surface currents of the ocean

Pattern of ocean currents is modified by the Coriolis Effect

Currents in North veer to the right

Currents in South veer to the left

Thermal energy is also transferred vertically via convection currents

(same principles as with air)

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Thermal Energy Transfer: Conduction, Convection, Radiation

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All things are made up of molecules When things get heated, they absorb heat energy With more energy, molecules are able to move faster When molecules move faster, the temperature rises What is Thermal Energy Thermal Energy is energy resulting from the motion of particles It is a form of kinetic energy and is transferred...

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Maths

Science

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You can download our open textbooks in different formats to use them in the way that suits you. The files can be big, so we don't make them available from our mobi site (the one you're currently viewing). Visit the desktop version of the site to access the download files for all of our titles.

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PHYSICS: ENERGY TRANSFORMATION [ AboodyTV ]

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Physics - Energy - Heat Transfer - Convection

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Law of Conservation of Matter | Science Lesson for Kids | Grades 3-5

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Want to learn about the law of conservation of matter? Watch this science video for kids in 3rd. 4th and 5th grade to help you learn it!

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Vacation or Conservation (Of Mass): Crash Course Kids #23.1

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Professor Dave Explains: Conservation of Matter

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Professor Dave Explains: Conservation of Matter

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Phase Change: Evaporation, Condensation, Freezing, Melting, Sublimation & Deposition

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Phase Change: Evaporation, Condensation, Freezing, Melting, Sublimation & Deposition

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All matter is made from atoms. Every substance (oxygen, lead, silver, neon ...) has a unique number of protons, neutrons, and electrons.
Oxygen, for example, has 8 protons, 8 neutrons, and 8 electrons.
Hydrogen has 1 proton and 1 electron.
Individual atoms can
combine with other atoms to form molecules.
Water molecules contain two atoms of hydrogen H and one atom of oxygen O
and is chemically called H2O.
Oxygen and
nitrogen are the major components of
air
and occur in nature as
diatomic (two atom) molecules.
Regardless of the type of molecule, matter normally
exists as either a solid, a liquid, or a gas.
We call this property of matter the phase of the matter.
The three normal phases of matter have unique characteristics which are listed on the
slide.

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Use this timeline for a look at some of the historical aspects in the development of our understanding of gases and plasmas.

1644 - Invention of the barometer

Evangelista Torricelli (1608-1647), a student of Galileo, invents the barometer to prove that the Earth's atmosphere has weight. His barometer is made by filling a glass tube, sealed at one end, with mercury and inverting into a bowl containing additional mercury.

1648 - Air pressure and altitude

Blaise Pascal (1623-1662) coins the term 'pressure' to indicate the weight of the air in the Earth's atmosphere. Using a Torricelli barometer, he compares pressure at the base of a mountain with the top. He discovers air pressure decreases with height above base level.

1662 - Boyle's Law

Robert Boyle (1627-1691) investigates the relationship between the volume of a fixed mass of gas, at constant temperature, and the pressure acting on it. He discovers that pressure is inversely proportional to volume. The Boyle's Law formula is written as P ₁V ₁=P ₂V ₂.

1702 - Amontons's Law

Guillaume Amontons (1663-1705) investigates the relationship between the pressure of a gas and its temperature. He discovers that, over the range from freezing to boiling water, the pressure increases by about one-third. Amontons's Law can be written as P ₁/T ₁=P ₂/T ₂.

1714 - First mercury-in-glass thermometer

Daniel Gabriel Fahrenheit (1686-1736) designs a mercury-in-glass thermometer and develops a temperature scale now named after him. The three calibration points used are a freezing mixture of ice/salt (0°F), a water/ice mixture (32°F) and human body temperature (96°F).

1742 - Celsius temperature scale

Anders Celsius (1701-1744) develops a new temperature scale based on the freezing and boiling points of water. Celsius assigns a value of 100° for the freezing point and 0° for the boiling point. A year after his death, the scale is reversed to make it more practical.

1780 - James Six's thermometer

James Six (1731-1793) invents a thermometer that allows maximum and minimum temperatures to be measured over a given time period. It proves to be most useful to meteorologists, and the basic design still remains in use today.

1787 - Charles's Law

With the recent development of accurate thermometers, Jacques Charles (1746-1823) is able to investigate the relationship between the volume of a gas and its temperature. The modern interpretation of his findings states that V ₁/T ₁=V ₂/T ₂.

1801 - Dalton's Law

John Dalton's (1776-1844) interest in the weather motivates him to study gases. He is the first to observe that the pressure of a mixture of gases is the sum of the pressures of the various gases in the mixture. Dalton's Law takes the form P T=P ₁+P ₂+P ₃+...

1803 - Henry's Law

William Henry (1774-1836) discovers that the solubility of a gas in a liquid is directly proportional to the gas pressure. Henry's Law takes the form S g=kP g where S g is the solubility of the gas and P g is the pressure of the gas.

1808 - Gay-Lussac's Law

Joseph Louis Gay-Lussac (1778-1850) formulates two gas laws. One, based on Amontons's Law, relates the pressure of a gas and its temperature. The other, combining volumes law, relates to gaseous reactions and the volume ratios of reactant and product gases.

1811 - Avogadro's Law

Amedeo Avogadro (1776-1856) extends the work of Gay-Lussac by proposing that gases consist of very small particles called molecules. His law states that equal volumes of gases under the same conditions of temperature and pressure contain equal numbers of molecules.

1834 - Ideal gas equation

Émile Clapeyron (1799-1864) is able to combine the laws of Boyle, Charles and Avogadro into a form known as the ideal gas equation. The modern form of this law states that PV=nRT, where n is the number of moles of gas and R the universal gas constant.

1846 - Graham's Law

Thomas Graham (1805-1869) studies the way gases mix by diffusion as well as how they effuse through a semi-permeable barrier. He is able to show that the rate of effusion is inversely proportional to the square root of the molecular mass of the gas.

1848 - Kelvin temperature scale

Lord Kelvin (William Thomson) (1824-1907) recognises the need for a temperature scale whose zero point is equivalent to "infinite cold" or absolute zero. He calculates that absolute zero is equivalent to -273°C. The Kelvin scale is used in modern day science.

1857 - Kinetic-molecular theory

Rudolf Clausius (1822-1888) develops the kinetic theory of gases into a more sophisticated and systematic form. He introduces the concept of mean free path and links temperature to gas particle speed. Physical properties of gases can now be explained in particle terms.

1873 - Equation of state

Johannes van der Waals (1837-1923) realises gas laws and kinetic-molecular theory are based on an idealised gas. He develops an equation based on real gas behaviour that takes account of attractive forces between gas particles and the volume occupied by each particle.

1879 - The fourth state of matter

Sir William Crookes uses an assembly (today known as a Crookes tube) to form ionised air by passing an electrical discharge through gas at low pressure in a sealed tube. He labels it "radiant matter" because of its luminous quality.

1898 -- Kinetic theory analogy

William Ramsay (1852-1916), best known for his discovery of the noble gases, writes a discussion paper on the kinetic theory of gases and uses the analogy of football players being likened to 'human molecules' moving and colliding as the game plays out.

1924 - Existence of the ionosphere

Edward Appleton finally establishes the presence of an electrified conductive layer in the Earth's upper atmosphere. This layer of ionised gas is given the name 'ionosphere' by Robert Watson-Watt in 1926.

1928 - Langmuir coins the term 'plasma'

Irvine Langmuir gives the name 'plasma' to this fourth state of matter, as the way electrified gas carries high speed electrons and ions reminds him of the way blood plasma carries red and white blood cells. It replaces Crookes's term 'radiant matter'.

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Use this timeline for a look at some of the historical aspects in the development of our understanding of gases and plasmas. Evangelista Torricelli (1608-1647), a student of Galileo, invents the barometer to prove that the Earth's atmosphere has weight.

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The world of gas can be a dense jungle of abbreviations and chemical formulas that is easy to get lost in. There are just so many types of gases to know. Some are similar, but all have slightly different origins, properties and applications. Unless you are a gas wizard, it is sometimes enough to leave your head spinning.

That is why we have made an overview that shows you what each gas consists of and how it can be used. Below, you can learn more about the different types of gases, and at the very bottom of this page, you find a poster with all of them on.

If you want a physical reminder, you can download and print the poster - and hang it on the wall of your office, break room, bedroom, bathroom or wherever else you want to be reminded of the difference between CNG, SNG, and all the other common fuel gases.

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The world of gas can be a dense jungle of abbreviations and chemical formulas that is easy to get lost in. There are just so many types of gases to know. Some are similar, but all have slightly different origins, properties and applications.

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The Ideal Gas Law: Crash Course Chemistry #12

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Liquid is one of the four common states of matter. The three others are gas, solid, and plasma. There are also some other exotic states of matter that have been discovered in recent years.

A liquid does not have a fixed shape, like a solid; instead it takes on the shape of the container that it is in. Liquids can flow. A liquid has a distinct surface, unlike a gas. This surface is called a free surface. For example, water in a glass has a surface where the water ends and the air above it begins.

When a liquid boils or evaporates, it becomes a gas. When a liquid freezes, it becomes a solid. For example, when liquid water boils, it becomes water vapor. When liquid water freezes, it becomes ice.

In everyday life we think of a liquid and a fluid as being the same thing. Scientists use the term " fluid" in a special way, though, to mean things that can flow. Liquids, gases, and plasmas are all fluids as far as scientists are concerned.

Water is probably what you think of when someone mentions a liquid. Milk, gasoline, and cooking oil are other common liquids. Some common substances, like the oxygen and nitrogen in air, are gases under "normal" circumstances but can become liquids if they are very, very cold. Mercury is a kind of metal that is a liquid at normal temperatures; it doesn't "freeze" and become a solid until cooled to -39° C (-38° F). Glass and steel become liquids when they are heated to very, very high temperatures.

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Liquid State of Matter - Windows to the Universe

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Liquid is one of the four common states of matter. The three others are gas, solid, and plasma. There are also some other exotic states of matter that have been discovered in recent years. A liquid does not have a fixed shape, like a solid; instead it takes on the shape of the container that it is in.

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(Image: © pedrosala | Shutterstock)

The liquid state of matter is an intermediate phase between solid and gas. Like the particles of a solid, particles in a liquid are subject to intermolecular attraction; however, liquid particles have more space between them, so they are not fixed in position. The attraction between the particles in a liquid keeps the volume of the liquid constant.

The movement of the particles causes the liquid to be variable in shape. Liquids will flow and fill the lowest portion of a container, taking on the shape of the container but not changing in volume. The limited amount of space between particles means that liquids have only very limited compressibility.

Cohesion and adhesion

Cohesion is the tendency for the same kind of particles to be attracted to one another. This cohesive "stickiness" accounts for the surface tension of a liquid. Surface tension can be thought of as a very thin "skin" of particles that are more strongly attracted to each other than they are to the particles surrounding them. As long as these forces of attraction are undisturbed, they can be surprisingly strong. For example, the surface tension of water is great enough to support the weight of an insect such as a water skipper. Water is the most cohesive nonmetallic liquid, according to the U.S. Geological Survey.

Cohesive forces are greatest beneath the surface of the liquid, where the particles are attracted to each other on all sides. Particles at the surface are more strongly attracted to the identical particles within the liquid than they are to the surrounding air. This accounts for the tendency of liquids to form spheres, the shape with the least amount of surface area. When these liquid spheres are distorted by gravity, they form the classic raindrop shape.

Adhesion is when forces of attraction exist between different types of particles. Particles of a liquid will not only be attracted to one another, but they are generally attracted to the particles that make up the container holding the liquid. Particles of the liquid are drawn up above the surface level of the liquid at the edges where they are in contact with the sides of the container.

The combination of cohesive and adhesive forces means that a slight concave curve, known as the meniscus, exists at the surface of most liquids. The most accurate measurement of the volume of a liquid in a graduated cylinder will be observed by looking at the volume marks closest to the bottom of this meniscus.

Adhesion also accounts for capillary action when a liquid is drawn up into a very narrow tube. One example of capillary action is when someone collects a sample of blood by touching a tiny glass tube to the blood droplet on the tip of a pricked finger.

Viscosity

Viscosity is a measure of how much a liquid resists flowing freely. A liquid that flows very slowly is said to be more viscous than a liquid that flows easily and quickly. A substance with low viscosity is considered to be thinner than a substance with higher viscosity, which is usually thought of as being thicker. For example, honey is more viscous than water. Honey is thicker than water and flows more slowly. Viscosity can usually be reduced by heating the liquid. When heated, the particles of the liquid move faster, allowing the liquid to flow more easily.

Evaporation

Because the particles of a liquid are in constant motion, they will collide with one another, and with the sides of the container. Such collisions transfer energy from one particle to another. When enough energy is transferred to a particle at the surface of the liquid, it will eventually overcome the surface tension holding it to the rest of the liquid. Evaporation occurs when surface particles gain enough kinetic energy to escape the system. As the faster particles escape, the remaining particles have lower average kinetic energy, and the temperature of the liquid cools. This phenomenon is known as evaporative cooling.

Volatility

Volatility can be thought of as how likely a substance will be to vaporize at normal temperatures. Volatility is more often a property of liquids, but some highly volatile solids may sublime at normal room temperature. Sublimation happens when a substance passes directly from solid to gas without passing through the liquid state.

When a liquid evaporates inside a closed container, the particles cannot escape the system. Some of the evaporated particles will eventually come into contact with the remaining liquid and lose enough of their energy to condense back into the liquid. When the rate of evaporation and the rate of condensation are the same, there will be no net decrease in the amount of liquid.

The pressure exerted by the vapor/liquid equilibrium in the closed container is called the vapor pressure. Increasing the temperature of the closed system will increase the vapor pressure, according to Purdue University's department of chemistry. Substances with high vapor pressures can form a high concentration of gas particles above the liquid in a closed system. This can be a fire hazard if the vapor is flammable. Any small spark, even one occurring from the friction between the gas particles themselves, can be enough to cause a catastrophic fire or even an explosion. The U.S. Occupational Safety and Health Administration (OSHA) requires Material Safety and Data Sheets to give information about the volatility and flammability of liquids in order to help prevent accidents from occurring.

Further reading

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(Image: © pedrosala | Shutterstock) The liquid state of matter is an intermediate phase between solid and gas. Like the particles of a solid, particles in a liquid are subject to intermolecular attraction; however, liquid particles have more space between them, so they are not fixed in position.

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How can this chemical be a liquid, solid. and gas at the same time?

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How can this chemical be a liquid, solid. and gas at the same time?

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How Can This Chemical Be a Solid, Liquid, and Gas at the Same Time?

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Primary Science Lesson Idea: What is a Solid? | Tigtag

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Solids are one of the three states of matter and, unlike liquids or gases, they have a definite shape that is not easy to change. Different solids have particular properties such as stretch, STRENGTH, or hardness that make them useful for different jobs. Most solids are made up of tiny crystals. This is because their particles are arranged in a regular pattern, called a CRYSTALLINE STRUCTURE.

Some solids can be hammered or squashed into many different shapes without breaking. They are known as malleable materials. Other solids, such as biscuits or glass, will not bend when hammered or squashed, but will break and split. These materials are brittle.

Shape memory metals can remember their shape. When brought to a certain temperature, these metals can be set to a shape that they never forget. They have many uses, including repairing broken bones. Even if the bones move, the metal always returns to its original shape, bringing the bones back to their correct position.

Some solids, such as the metal copper, can be pulled and stretched easily into extremely thin wires. They are known as ductile materials. They have this property because their particles are not held in a rigid structure, but are arranged in rows that can slide past one another. Copper can be stretched into a thread half the width of a human hair, and is used in many kinds of wiring, including electrical and telephone wiring.

Some solids, such as steel or concrete, are difficult to break, even if they are made to carry a heavy weight. This is because their particles are bound together very strongly. Such materials are said to have high strength and are used to construct bridges and buildings. Strength is a different property from hardness. Hard materials cannot be bent or scratched easily.

Most solids, such as metals, salt, and sugar, are made up of tiny crystals. Their particles are arranged in regular three-dimensional patterns such as cubes or hexagonal shapes. Not all solids are like this, however. The particles of glass, for example, are not arranged in a regular pattern, and so glass does not have a crystalline structure. Its structure is described as amorphous.

Copyright © 2007 Dorling Kindersley

Solids are one of the three states of matter and, unlike liquids or gases, they have a definite shape that is not easy to change. Different solids have particular properties such as stretch, STRENGTH, or hardness that make them useful for different jobs. Most solids are made up of tiny crystals. This is because their particles are arranged in a regular pattern, called a CRYSTALLINE STRUCTURE.

Some solids can be hammered or squashed into many different shapes without breaking. They are known as malleable materials. Other solids, such as biscuits or glass, will not bend when hammered or squashed, but will break and split. These materials are brittle.

Shape memory metals can remember their shape. When brought to a certain temperature, these metals can be set to a shape that they never forget. They have many uses, including repairing broken bones. Even if the bones move, the metal always returns to its original shape, bringing the bones back to their correct position.

Some solids, such as the metal copper, can be pulled and stretched easily into extremely thin wires. They are known as ductile materials. They have this property because their particles are not held in a rigid structure, but are arranged in rows that can slide past one another. Copper can be stretched into a thread half the width of a human hair, and is used in many kinds of wiring, including electrical and telephone wiring.

Some solids, such as steel or concrete, are difficult to break, even if they are made to carry a heavy weight. This is because their particles are bound together very strongly. Such materials are said to have high strength and are used to construct bridges and buildings. Strength is a different property from hardness. Hard materials cannot be bent or scratched easily.

Most solids, such as metals, salt, and sugar, are made up of tiny crystals. Their particles are arranged in regular three-dimensional patterns such as cubes or hexagonal shapes. Not all solids are like this, however. The particles of glass, for example, are not arranged in a regular pattern, and so glass does not have a crystalline structure. Its structure is described as amorphous.

Copyright © 2007 Dorling Kindersley

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Solids are one of the three states of matter and, unlike liquids or gases, they have a definite shape that is not easy to change. Different solids have particular properties such as stretch, STRENGTH, or hardness that make them useful for different jobs. Most solids are made up of tiny crystals.

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A solid is a state of matter characterized by particles arranged such that their shape and volume are relatively stable. The constituents of a solid tend to be packed together much closer than the particles in a gas or liquid. The reason a solid has a rigid shape is that the atoms or molecules are tightly connected via chemical bonds. The bonding may produce either a regular lattice (as seen in ice, metals, and crystals) or an amorphous shape (as seen in glass or amorphous carbon). A solid is one of the four fundamental states of matter, along with liquids, gases, and plasma.

Solid-state physics and solid-state chemistry are two branches of science dedicated to studying the properties and synthesis of solids.

Examples of Solids

The matter with a defined shape and volume is solid. There are many examples:

A brick

A penny

A piece of wood

A chunk of aluminum metal (or any metal at room temperature except mercury)

Diamond (and most other crystals)

Examples of things that are not solids include liquid water, air, liquid crystals, hydrogen gas, and smoke.

Classes of Solids

The different types of chemical bonds that join the particles in solids exert characteristic forces that can be used to classify solids. Ionic bonds (e.g. in table salt or NaCl) are strong bonds that often result in crystalline structures that may dissociate to form ions in water. Covalent bonds (e.g., in sugar or sucrose) involve the sharing of valence electrons. Electrons in metals seem to flow because of metallic bonding. Organic compounds often contain covalent bonds and interactions between separate portions of the molecule due to van der Waals forces.

Major classes of solids include:

Minerals: Minerals are natural solids formed by geological processes. A mineral has a uniform structure. Examples include diamond, salts, and mica.

Metals: Solid metals include elements (e.g., silver) and alloys (e.g., steel). Metals are typically hard, ductile, malleable, and excellent conductors of heat and electricity.

Ceramics: Ceramics are solids consisting of inorganic compounds, usually oxides. Ceramics tend to be hard, brittle, and corrosion-resistant.

Organic Solids: Organic solids include polymers, wax, plastics, and wood. Most of these solids are thermal and electrical insulators. They typically have lower melting and boiling points than metals or ceramics.

Composite Materials: Composite materials are those which contain two or more phases. An example would be a plastic containing carbon fibers. These materials yield properties not seen in the source components.

Semiconductors: Semiconducting solids have electrical properties intermediate between those of conductors and insulators. The solids may be either pure elements, compounds, or doped materials. Examples include silicon and gallium arsenide.

Nanomaterials: Nanomaterials are tiny solid particles at the nanometer size. These solids may display very different physical and chemical properties from large-scale versions of the same materials. For example, gold nanoparticles are red and melt at a lower temperature than gold metal.

Biomaterials: Biomaterials are natural materials, such as collagen and bone, that are often capable of self-assembly.

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The Definition of a Solid, as the Term Is Used in the Sciences

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A solid is a state of matter characterized by particles arranged such that their shape and volume are relatively stable. The constituents of a solid tend to be packed together much closer than the particles in a gas or liquid. The reason a solid has a rigid shape is that the atoms or molecules are tightly connected via chemical bonds.

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(Image: © Arisa J | Shutterstock )

Solid is one of the three main states of matter, along with liquid and gas. Matter is the "stuff" of the universe, the atoms, molecules and ions that make up all physical substances. In a solid, these particles are packed closely together and are not free to move about within the substance. Molecular motion for the particles in a solid is confined to very small vibrations of the atoms around their fixed positions; therefore, solids have a fixed shape that is difficult to change. Solids also have a definite volume; that is, they keep their size no matter how you try to change them.

Solids are divided into two main categories, crystalline solids and amorphous solids, based on how the particles are arranged.

Crystalline solids

Crystalline solids, or crystals, are regarded as "true solids." Minerals are crystalline solids. Common table salt is one example of this kind of solid. In crystalline solids, the atoms, ions or molecules are arranged in an ordered and symmetrical pattern that is repeated over the entire crystal. The smallest repeating structure of a solid is called a unit cell, which is like a brick in a wall. Unit cells combine to form a network called a crystal lattice. There are 14 types of lattices, called Bravais lattices (named after Auguste Bravais, a 19th-century French physicist), and they are classified into seven crystal systems based on the arrangement of the atoms. The ChemWiki page at the University of California, Davis lists these systems as cubic, hexagonal, tetragonal, rhombohedral, orthorhombic, monoclinic and triclinic.

Aside from the regular arrangement of particles, crystalline solids have several other characteristic properties. They are generally incompressible, meaning they cannot be compressed into smaller shapes. Because of the repeating geometric structure of the crystal, all the bonds between the particles have equal strength. This means that a crystalline solid will have a distinct melting point, because applying heat will break all the bonds at the same time.

Crystalline solids also exhibit anisotropy. This means that properties such as refractive index (how much light bends when passing through the substance), conductivity (how well it conducts electricity) and tensile strength (the force required to break it apart) will vary depending on the direction from which a force is applied. Crystalline solids also exhibit cleavage; when broken apart, the pieces will have planed surfaces, or straight edges.

Types of crystalline solids

There are four types of crystalline solids: ionic solids, molecular solids, network covalent solids and metallic solids.

Ionic solids

Ionic compounds form crystals that are composed of oppositely charged ions: a positively charged cation and a negatively charged anion. Because of the strong attraction between opposite charges, it takes a lot of energy to overcome ionic bonds. This means that ionic compounds have very high melting points, often between 300 and 1,000 degrees Celsius (572 to 1,832 degrees Fahrenheit).

While the crystals themselves are hard, brittle and nonconductive, most ionic compounds can be dissolved in water, forming a solution of free ions that will conduct electricity. They may be simple binary salts like sodium chloride (NaCl), or table salt, where one atom of a metallic element (sodium) is bonded to one atom of a nonmetallic element (chlorine). They may also be composed of polyatomic ions such as NH ₄NO ₃ (ammonium nitrate). Polyatomic ions are groups of atoms that share electrons (called covalent bonding) and function in a compound as if they constituted a single charged ion.

Molecular solids

Molecular solids are composed of covalently bonded molecules attracted to each other by electrostatic forces (called van der Waals forces, according to the HyperPhysics website). Because covalent bonding involves sharing electrons rather than outright transfer of those particles, the shared electrons may spend more time in the electron cloud of the larger atom, causing weak or shifting polarity. This electrostatic attraction between the two poles (dipoles) is much weaker than ionic or covalent bonding, so molecular solids tend to be softer than ionic crystals and have lower melting points (many will melt at less then 100 C, or 212 F). Most molecular solids are nonpolar. These nonpolar molecular solids will not dissolve in water, but will dissolve in a nonpolar solvent, such as benzene and octane. Polar molecular solids, such as sugar, dissolve easily in water. Molecular solids are nonconductive.

Examples of molecular solids include ice, sugar, halogens like solid chlorine (Cl ₂), and compounds consisting of a halogen and hydrogen such as hydrogen chloride (HCl). Fullerene "buckyballs" are also molecular solids.

Network covalent solids

In a network solid, there are no individual molecules. The atoms are covalently bonded in a continuous network, resulting in huge crystals. In a network solid, each atom is covalently bonded to all the surrounding atoms. Network solids have similar properties to ionic solids. They are very hard, somewhat brittle solids with extremely high melting points (higher than 1,000 C or 1,800 F). Unlike ionic compounds, they do not dissolve in water, nor do they conduct electricity.

Examples of network solids include diamonds, amethysts and rubies.

Metals are opaque, lustrous solids that are both malleable and ductile. Malleable means they are soft and can be shaped or pressed into thin sheets, while ductile means they can be pulled into wires. In a metallic bond, the valence electrons are not donated or shared as they are in ionic and covalent bonding. Rather, the electron clouds of adjacent atoms overlap so that electrons become delocalized. The electrons move with relative freedom from one atom to another throughout the crystal.

A metal may be described as a lattice of positive cations within a "sea" of negative electrons. This electron mobility means that metals are highly conductive of heat and electricity. Metals tend to have high melting points, though notable exceptions are mercury, which has a melting point of minus 37.84 degrees Fahrenheit (minus 38.8 Celsius), and phosphorous, with a melting point of 111.2 F (44 C).

An alloy is a solid mixture of a metallic element with another substance. While pure metals can be overly malleable and heavy, alloys are more workable. Bronze is an alloy of copper and tin, while steel is an alloy of iron, carbon and other additives.

Amorphous solids

In amorphous solids (literally "solids without form"), the particles do not have a repeating lattice pattern. They are also called "pseudo solids." Examples of amorphous solids include glass, rubber, gels and most plastics. An amorphous solid does not have a definite melting point; instead, it melts gradually over a range of temperatures, because the bonds do not break all at once. This means an amorphous solid will melt into a soft, malleable state (think candle wax or molten glass) before turning completely into a liquid.

Amorphous solids have no characteristic symmetry, so they do not have regular planes of cleavage when cut; the edges may be curved. They are called isotropic because properties such as refractive index, conductivity and tensile strength are equal regardless of the direction in which a force is applied.

Additional resources

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(Image: © Arisa J | Shutterstock ) Solid is one of the three main states of matter, along with liquid and gas. Matter is the "stuff" of the universe, the atoms, molecules and ions that make up all physical substances. In a solid, these particles are packed closely together and are not free to move about within the substance.

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Characteristics of Gases, Liquids and Solids 

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Characteristics of Gases, Liquids and Solids 

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Gases, liquids and solids are all made up of microscopic particles, but the behaviors of these particles differ in the three phases.
The following figure illustrates the microscopic differences.

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Matter: Definition & the Five States of Matter

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The four fundamental states of matter are solid, liquid, gas and plasma, but there others, such as Bose-Einstein condensates and time crystals, that are man-made.

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Back to the water cycle on the USGS Water Science School.

Fog

Fog is just a cloud that happens to be hanging around on the Earth's surface.

Fog contains very tiny liquid water particles, like a cloud, and floats, like a cloud. Actually, fog IS a cloud, but one that swirls around your feet instead of high in the sky. Fog forms when air containing invisible water vapor encounters cooler temperatures (here, next to the ground) and the water vapor condenses out into liquid water-the cloud.

In this picture, as the day warms the air next to the ground will warm, too, and the fog particles will again evaporate back into invisible water vapor.

Groundwater flow

If you pour a glass of water onto the ground it usually sinks right in ( infiltration), so you can imagine how much water sinks into the ground during a major storm ( Find out here). Here in Atlanta, Ga, USA it rains about 50 inches/year. Over a 100 square mile (10 miles by 10 miles) area that means 87,000 billion gallons of water falls, with much of it soaking into the ground to recharge groundwater.

Yes, water below your feet is moving all the time, but, no, if you have heard there are rivers flowing below ground, that is not true.

Groundwater flow. Relate to recharge a battery.

Groundwater

When you are standing on the ground, you're not only standing on dirt, but on water-a lot of water. The dirt and rock below your feet contains lots of spaces and cracks, and water can exist in these open spaces. In fact, over 20 times the amount of water in all of Earth's rivers and lakes is in the ground.

When you pour a glass of water on your yard, the water sinks (infiltrates) into the ground and gets back into being a vital part of the global water cycle.

Of course, the rock underground is different all over the world, so how much and where water occurs of water underground is different everywhere. Deep in the ground, the rock becomes very hard and solid (no open spaces to hold water), and it also gets very hot, so no liquid water is found deep in the Earth.

Ice and snow

Ice and glaciers are part of the water cycle, even though the water moving in them changes very slowly. The amount of ice on the Earth goes up and down as the world's climate cools and warms over thousands of years.

Lucky for us we're now in a warmer phase of the Earth's history, but the last Ice Age was only 18,000 years ago. At that time, ice covered the northern part of North America.

Ice and glaciers are still around today, as this picture shows. In fact, most of the world's freshwater, about 68 percent, is locked up in ice, snow, and glaciers.

Oceans

If you look at this picture (or click on it for a larger version) you see that "tiny" blue ball sitting in the middle of the United States-if all the water on, in, and above the Earth was collected in one big ball, this is the size it would be.

The oceans are, by far, the largest reservoir of water on earth-over 96% of all of Earth's water exists in the oceans.

Oceans are important to the water cycle because almost all the water that evaporates from liquid to water vapor (which forms clouds) comes from the oceans.

Precipitation

The air is full of water, even if you can't see it. Higher in the sky where it is colder than at the land surface, invisible water vapor condenses into tiny liquid water droplets-clouds. When the cloud droplets combine to form heavier cloud drops, it can start to rain, snow, hail....all forms of precipitation.

The amount of precipitation that falls is different all around the world. In deserts, such as in Chile, it may only rain one inch per year, while on some mountains in Hawaii and in India, it can rain more than 600 inches per year. That is almost 2 inches every day!

Precipitation is the "exit ramp" back to earth from the water-cycle superhighway in the sky that is moving clouds all around the globe.

Rivers

Most of the rain that falls stays on the land surface and, due to gravity, starts running downhill. This runoff water will accumulate in creeks ... I mean, in streams ...no, I mean, in rivers. Actually, no matter what you call them, rivers are responsible for moving a lot of water off of the land and back into oceans.

Of course, plants, animals, and people interact with rivers, as all kinds of life seems to thrive around rivers. If you look at a map of the world, you see how people naturally build their cities next to rivers.

And, as this satellite picture of the Nile River in Egypt, you can often pick out the rivers because of the green growth growing along them.

Seepage

You know all about seepage. When you spill your red fruit drink onto your Mom's white carpet, she rushes (after glaring at you) to get a sponge to soak up the liquid before it "seeps down into the carpet".

With the water cycle, seepage occurs when precipitation falls on the landscape and starts to soak into the ground. The "Why?" this happens is simply gravity. But, seepage doesn't just happen downward! Water seeps upwards and sideways, too, from the ground into the bottom of rivers, lakes, and the oceans. Some of the water you see flowing in a river has come up from the ground.

The Sun

Who's the Boss? The sun is the real boss of the water cycle, and it doesn't even live here on Earth. The sun is what makes the water cycle work. The sun provides what almost everything on Earth needs to go-energy, or heat.

The sun's heat allows liquid water to evaporate into water vapor, which in the main way water gets from the land surface back into the sky.

The sun also participates in moving water around the Earth by being the reason winds exist. The winds move clouds and the weather all over the place; all of this mixing up and moving is an important part of the water cycle.

Evapotranspiration (Evaporation and transpiration)

When a person breathes, their breath contains water molecules. All the plants around you are "breathing" and releasing water, too. The term is called "transpiration", and although a brussels sprout doesn't have a mouth, it has tiny holes in its leaves that allow water to leave the leaf, via evaporation, and go into the air.

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Interactive Water Cycle Diagram for Kids (Intermediate)

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The Water Cycle for Kids, from the USGS Water Science School.