Matter

Learning about Matter

Building Blocks of Matter?

Atoms are building blocks. If you want to create a language, you'll need an alphabet. If you want to build molecules, you will need atoms of differentelements. Elements are the alphabet in the language of molecules. Each element is a little bit different from the rest.

Why are we talking about elements when this is the section on atoms? Atoms are the general term used to describe pieces of matter. You have billions of billions of atoms in your body. However, you may only find about 40 elements. You will find billions of hydrogen (H) atoms, billions ofoxygen (O) atoms, and a bunch of others. All of the atoms are made of the same basic pieces, but they are organized in different ways to make unique elements. In chemistry, you are working with almost 120 elements. When you combine them, you can make millions of different molecules.

Molecules are groups of atoms bonded together in the same way that words are groups of letters. An "A" will always be an "A" no matter what word it is in. A sodium (Na) atom will always be a sodium atom no matter what compound it is in. While the atoms have different masses and organization for each element, they are all built with the same parts. Electrons, protons, and neutrons make the Universe the way it is.

Super-tiny subatomic particles are used to create the parts of atoms. Protons, neutrons, and electrons can then organize to form atoms. Atoms are then used to create the molecules around us. There are almost 120 elements that can be found in the molecules we know. Smaller molecules can work together and build macromolecules.

Atoms are the foundation of chemistry. They are the basis for everything in the Universe. As you know, matter is composed of atoms. Solids are made of densely packed atoms while gases have atoms that are spread out.

Learn more about Atoms here.

What is an atom? | Chemistry | the virtual school

What is Matter?

Matter is anything that has mass and volume (occupies space). Matter is everything around you. Atoms and molecules are all composed of matter. Matter is anything that has mass and takes up space. If you are new to the idea of mass, it is the amount of stuff in an object. We talk about the difference between mass and weight in another section. Matter is sometimes related to light and electromagnetic radiation. Even though matter can be found all over the Universe, you will only find it in a few forms on Earth. We cover five states of matter on the site. Each of those states is sometimes called a phase. There are many other states of matter that exist in extreme environments. Scientists will probably discover more states as we continue to explore the Universe.

What is Matter?

The Learning Channel's "What is Matter?"

Five States of Matter

You should know about solids, liquids, gases, plasmas, and one state called the Bose-Einstein condensate (BEC). Scientists have always known about solids, liquids, and gases. Plasma was a new idea when it was identified by William Crookes in 1879. The scientists who worked with the Bose-Einstein condensate received a Nobel Prize for their work in 1995.

What makes a state of matter? It's about the physical state of the molecules and atoms. Think about solids. They are often hard and brittle. Liquids are fluidy, can move around a little, and fill up containers. Gases are always around you, but the molecules of a gas are much farther apart than the molecules in a liquid. If a gas has an odor, you’ll be able to smell it before you can see it. The BEC is all about atoms that are even closer and less energetic than atoms in a solid.

Changing States of Matter

Molecules can move from one physical state to another and not change their basic structure. Oxygen (O2) as a gas has the same chemical properties as liquid oxygen. The liquid state is colder and denser, but the molecules (the basic parts) are still the same. Water (H2O) is another example. A water molecule is made up of two hydrogen (H) atoms and one oxygen (O) atom. It has the same molecular structure whether it is a gas,liquid, or solid. Although its physical state may change, its chemical state remains the same.

So you're asking, "What is a chemical change?" Let's start with a glass of pure water. If the formula of water were to change, that would be a chemical change. If you could add a second oxygen atom to a water molecule, you would have hydrogen peroxide (H2O2). The molecules would not be water anymore. The reality of creating hydrogen peroxide is more difficult. Chemical changes occur when the bonds between atoms in a molecule are created or destroyed. Changes in the physical state are related to changes in the environment such as temperature, pressure, and other physical forces. Generally, the basic chemical structure does not change when there is a physical change. Of course, in extreme environments such as the Sun, no molecule is safe from destruction.

All matter can move from one state to another. It may require extreme temperatures or extreme pressures, but it can be done. Sometimes a substance doesn't want to change states. You have to use all of your tricks when that happens. To create a solid, you might have to decrease the temperature by a huge amount and then add pressure. For example, oxygen (O2) will solidify at -361.8 degrees Fahrenheit (-218.8 degrees Celsius) at standard pressure. However, it will freeze at warmer temperatures when the pressure is increased.

Some of you know about liquid nitrogen (N2). It is nitrogen from the atmosphere in a liquid form and it has to be super cold to stay a liquid. What if you wanted to turn it into a solid but couldn't make it cold enough to solidify? You could increase the pressure in a sealed chamber. Eventually you would reach a point where the liquid became a solid. If you have liquid water (H2O) at room temperature and you wanted water vapor, you could use a combination of high temperatures or low pressures to solve your problem.

Points of Change

Phase changes happen when certain points are reached. Sometimes a liquid wants to become a solid. Scientists use something called a freezing pointor melting point to measure the temperature at which a liquid turns into a solid. There are physical effects that can change the melting point.Pressure is one of those effects. When the pressure surrounding a substance increases, the freezing point and other special points also go up. It is easier to keep things solid when they are under greater pressure.

Generally, solids are more dense than liquids because their molecules are closer together. The freezing process compacts the molecules into a smaller space.

There are always exceptions in science. Water is special on many levels. It has more space between its molecules when it is frozen. The molecules organize in a specific arrangement that takes up more space than when they are all loosey-goosey in the liquid state. Because the same number of molecules take up more space, solid water is less dense than liquid water.

Solid to Liquid

Imagine that you are a solid. You're a cube of ice sitting on a counter. You dream of becoming liquid water. You need some energy. Heat is probably the easiest energy you can use to change your physical state. The atoms in a liquid have more energy than the atoms in a solid.

There is a special temperature for every substance called the melting point. When a solid reaches the temperature of its melting point, it can become a liquid. For water, the temperature needs to be a little over zero degrees Celsius (0oC) for you to melt.

If you were salt, sugar, or rock, your melting point is higher than that of water. How do you know that fact? If their melting points were lower, they would also be liquids at room temperature. The reverse of the melting process is called freezing. Liquid water freezes and becomes solid ice when the molecules lose energy.

Solid to Gas back to Solid

You are used to solids melting and becoming liquids. Some of you may have also seen a solid become a gas. It's a process called sublimation. The easiest example of sublimation might be dry ice. Dry ice is solid carbon dioxide (CO2). Amazingly, when you leave dry ice out in a room, it just turns into a gas. Have you ever heard of liquid carbon dioxide? It can be made, but not in normal situations. Coal is another example of a compound that will not melt at normal atmospheric pressures. It will sublimate at very high temperatures.

Can you go from a gas to a solid? Sure. Deposition occurs when a gas becomes a solid without going through the liquid state of matter. Those of you who live near the equator may not have seen it, but closer to the poles we see frost on winter mornings. Those little frost crystals on plants build up when water vapor from the air becomes a solid on the leaves of plants.

Liquid to Gas back to Liquid

When you are a liquid and want to become a gas, you need to find a lot ofenergy. Once you can direct that energy into your molecules, they will start to vibrate. If they vibrate enough, they can escape the limitations of the liquid environment and become a gas. When you reach your boiling point, the molecules in your system have enough energy to become a gas.

The reverse is true if you are a gas. You need to lose some energy from your very excited gas atoms. The easy answer is to lower the surrounding temperature. When the temperature drops, energy will be transferred out of your gas atoms into the colder environment. When you reach the temperature of the condensation point, you become a liquid. If you were steam over a boiling pot of water and you hit a wall, the wall would be so cool that you would quickly become a liquid. The wall absorbed some of your extra energy.

Gas to Plasma back to Gas

Let's finish up by imagining you're a gas like neon (Ne). You say, "Hmmmm. I'd like to become a plasma. They are too cool!" As a gas, you're already halfway there, but you still need to tear off a bunch ofelectrons from your atoms. The gas needs to ionize. Electrons have a negative charge. Eventually, you'll have groups of positively and negatively charged particles in almost equal concentrations. They wind up in a big plasma ball. Because the positive and negative charges are in equal amounts, the charge of the entire plasma is close to neutral. Neutral happens when a whole bunch of positive particles cancel out the charges of an equal bunch of negatively charged particles.

Plasma can be made from a gas if a lot of energy is pushed into the gas. In the case of neon, it is electrical energy that pulls the electrons off. When it is time to become a gas again, just flip the neon light switch off. Without theelectricity to energize the atoms, the neon plasma returns to its gaseous state. We have a special world here on Earth. We have an environment where you don't find a lot of everyday plasma. Once you leave the planet and travel through the Universe, you will find plasma everywhere. It's in stars and all of the space in between.

States of Matter

We look at five states of matter on the site. Solids, liquids, gases, plasmas, and Bose-Einstein condensates (BEC) are different states that have different physical properties. Each of these states is also known as a phase. Elements and compounds can move from one phase to another when specific physical conditions change. For example, when the temperature of a system goes up, the matter in the system becomes more excited and active. If enough energy is placed in a system, a phase change may occur as the matter moves to a more active state. Think about it this way. Let’s say you have a glass of water (H2O). When the temperature of the water goes up, the molecules get more excited and bounce around a lot more. If you give a liquidwater molecule enough energy, it escapes the liquid phase and becomes a gas. Have you ever noticed that you can smell a turkey dinner after it starts to heat up? As the energy of the molecules inside the turkey heat up, they escape as a gas. You are able to smell those volatile molecules that are mixed in the air.

Physical State of Matter

"Phase" describes a physical state of matter. The key word to notice is physical. Things only move from one phase to another by physical means. If energy is added (like increasing the temperature) or if energy is taken away (like freezing something), you have created a physical change. When molecules move from one phase to another they are still the same substance. There is water vapor above a pot of boiling water. That vapor (or gas) can condense and become a drop of water in the cooler air. If you put that liquid drop in the freezer, it would become a solid piece of ice. No matter what physical state it was in, it was always water. It always had the same chemical properties. On the other hand, a chemical change would build or break the chemical bonds in the water molecules. If you added a carbon (C) atom, you would have formaldehyde (H2CO). If you added an oxygen (O) atom, you would create hydrogen peroxide (H2O2). Neither new compound is anything like the original water molecule. Generally, changes in the physical state do not lead to any chemical change in molecules.

Chemical Changes vs Physical Changes

It is important to understand the difference between chemical andphysical changes. Some changes are obvious, but there are some basic ideas you should know. Physical changes are usually about states and physical states of states. Chemical changes happen on a molecular level when you have two or more molecules that interact. Chemical changes happen when atomic bonds are broken or created during chemicalreactions.

No Change to Molecules

When you step on a can and crush it, you have forced a physical change. However, you only changed the shape of the can. It wasn't a change in the state of matter because the energy in the can did not change. Also, since this was a physical change, the molecules in the can are still the same molecules. No chemical bonds were created or broken.

When you melt an ice cube (H2O), you have a physical change because you add energy. In this example, you added enough energy to create a phase change from solid to liquid. Physical actions, such as changing temperature or pressure, can cause physical changes. No chemical changes took place when you melted the ice. The water molecules are still water molecules.

Changing the Molecules

Chemical changes happen on a much smaller scale. While some experiments show obvious chemical changes, such as a color change, most chemical changes are not visible. The chemical change as hydrogen peroxide (H2O2) becomes water cannot be seen since both liquids are clear. However, behind the scenes, billions of chemical bonds are being created and destroyed. In this example, you may see bubbles of oxygen (O2) gas. Those bubbles are evidence of the chemical changes.

Melting a sugar cube is a physical change because the substance is still sugar. Burning a sugar cube is a chemical change. Fire activates a chemical reaction between sugar and oxygen. The oxygen in the air reacts with the sugar and the chemical bonds are broken.

Iron (Fe) rusts when it is exposed to oxygen gas in the air. You can watch the process happen over a long period of time. The molecules change their structure as the iron is oxidized, eventually becoming iron oxide (Fe2O3). Rusty pipes in abandoned buildings are real world examples of the oxidation process.

Isomers

Some chemical changes are extremely small and happen over a series of steps. The resulting compounds might have the same number of atoms, but they will have a different structure or combination of atoms.

The sugars glucose, galactose, and fructose all have six carbon atoms, twelve hydrogen atoms, and six oxygen atoms (C6H12O6). Even though they are made of the same atoms, they have very different shapes and are called isomers. Isomers have atoms bonded in different orders.

Each of the sugars goes through different chemical reactions because of the differences in their molecular structure. Scientists say that the arrangement of atoms allows for a high degree of specificity, especially in the molecules of living things. Specificity means the molecules will only work in specific reactions, not all of them. For example, your body uses glucose as an energy source. If you eat galactose molecules, they need to be converted into glucose before your body can use them.

Solid Basics

What is one physical characteristic of a solid? Solids can be hard like a rock, soft like fur, big like an asteroid, or small like grains of sand. The key is that solids hold their shape and they don't flow like a liquid. A rock will always look like a rock unless something happens to it. The same goes for a diamond. Solids can hold their shape because their molecules are tightly packed together.

You might ask, "Is baby power a solid? It's soft and powdery." Baby power is also a solid. It's just a ground down piece of talc. Even when you grind a solid into powder, you will see tiny pieces of that solid under a microscope. Liquids will flow and fill up any shape of container. Solids like to hold their shape.

In the same way that a large solid holds its shape, the atoms inside of a solid are not allowed to move around too much.Atoms and molecules in liquids andgases are bouncing and floating around, free to move where they want. The molecules in a solid are stuck in a specific structure or arrangement of atoms. The atoms still vibrate and the electrons fly around in their orbitals, but the entire atom will not change its position.

Solid Mixtures

Solids can be made of many things. They can have pure elements or a variety of compounds inside. When you have a solid with more than one type of compound, it is called a mixture. Most rocks are mixtures of many different compounds. Concrete is a good example of a man-made solid mixture.

Granite is a mixture you might find when you hike around a national park. Granite is made of little pieces of quartz, mica, and other particles. Because all of the little pieces are spread through the rock in an uneven way, scientists call it a heterogeneous mixture. Heterogeneous mixtures have different concentrations of compounds in different areas of the mixture. For example, there might be a lot of quartz and very little feldspar in one part of the granite, but only a few inches away those amounts might flip.

Crystals

On the other end of the spectrum is something called a crystal. A crystal is a form of solid where the atoms are arranged is a very specific order. Crystals are often pure substances and not all substances can form crystals because it is a very delicate process. The atoms are arranged in a regular repeating pattern called a crystal lattice. Table salt (NaCl) is a great example of a crystal you can find around your house. The sodium (Na) and chlorine (Cl) atoms arrange themselves in a specific pattern to form the cubic salt crystals.

Allotropes

A diamond is another good example of a crystal. Diamonds are a crystal form of pure carbon (C). The carbon atoms of a diamond are connected in a very compact and structured way. The carbon atoms found in graphite (in pencils) have a different crystalline arrangement. According to the Mohs hardness scale, diamonds are very hard with a value of 10 while graphite is very soft with a value of 1.5. The two different structures of carbon atoms (tetrahedron versus hexagon) are called allotropes.

Liquid Basics

Liquids are the second state of matter we will talk about. Solids are objects you can hold and maintain their shape. Gases are floating around you or trapped in bubbles. Liquids are found between the solid and gas states. Examples of liquids at room temperature include water (H2O), blood, and even honey. If you have different types of molecules dissolved in a liquid, it is called a solution. Honey is a solution of sugar, water, and other molecules.

Liquids fill the shape of any container they are in. If you pour water in a cup, it will fill up the bottom of the cup first and then fill the rest. If you freeze that cup of water, the ice will be in the shape of the cup.

The top of a liquid will usually have a flat surface. That flat surface is the result of gravity pulling on the liquid molecules. Let’s go back to the cup for a moment. If you put an ice cube (solid) into the cup, it will sit there and not change shape. As the cube warms and melts, the liquid water will fill the bottom of the cup and have a flat surface on top.

Pushing on a Liquid

Another trait of liquids is that they are difficult to compress. When you compress something, you take a certain amount of material and force it into a smaller space or volume. You force the atoms closer together. Most solids are very difficult to compress while gases are easier. You can find compressed gases in SCUBA air tanks. Liquids are in the middle, but tend to be difficult to compress because the molecules are already close together. You probably can’t compress a liquid with your hands. It takes a lot of force.

Many shock absorbers found in cars and trucks have compressed liquids, such as oils, in sealed tubes. Without shocks, there would be a very rough ride for the driver and a lot of stress on the structure of the car. The shocks counter the extremes of the up and down motion by acting as a dampening device.

Molecules Sticking Together

Intermolecular forces are found in all substances. Some of the forces bring molecules together while others push them apart. Solids are locked together and you have to force them apart. Gases bounce everywhere and spread out. Many liquids want to stick together because of cohesive(sticky) forces that pull the molecules together.

When you place a drop of water on a piece of glass, you will see it stay together as a drop. Cohesive forces keep the drop from spreading out. Cohesive forces also keep water molecules together if there is a drip on your faucet. The water sticks together until it is too heavy. It drips when the weight of the water drop overcomes the cohesive forces holding it all together.

Evaporation occurs when individual liquid molecules gain enough energy to escape the system and become a gas. The extra energy allows individual molecules to overcome the intermolecular forces within the liquid.

Evaporation of Liquids

Sometimes a liquid can be sitting in one place (maybe a puddle) and its molecules will become a gas. That's the process called evaporation. It can happen when liquids are cold or when they are warm. It happens more often with warmer liquids. You probably remember that when matter has a higher temperature, the molecules have a higher energy. When the energy in specific molecules reaches a certain level, they can have a phase change. Evaporation is all about the energy in individual molecules, not about the average energy of a system. The average energy can be low and the evaporation still continues.

You might be wondering how that can happen when the temperature is low. It turns out that all liquids can evaporate at room temperature and normal air pressure. Evaporation happens when atoms or molecules escape from the liquid and turn into a vapor. Not all of the molecules in a liquid have the same energy. When you have a puddle of water (H2O) on a windy day, the wind can cause an increased rate of evaporation even when it is cold out.

Energy Transfer

The energy you can measure with a thermometer is really the average energy of all the molecules in the system. There are always a few molecules with a lot of energy and some with barely any energy at all. There is a variety, because the molecules in a liquid can move around. The molecules can bump into each other, and when they hit... Blam! A little bit of energy moves from one molecule to another. Since that energy is transferred, one molecule will have a little bit more and the other will have a little bit less. With trillions of molecules bouncing around, sometimes individual molecules gain enough energy to break free. They build up enough power to become a gas once they reach a specific energy level. In a word, when the molecule leaves, it has evaporated.

The rate of evaporation can also increase with a decrease in the gas pressure around a liquid. Molecules like to move from areas of higher pressure to lower pressure. The molecules are basically sucked into the surrounding area to even out the pressure. Once the vapor pressure of the system reaches a specific level, the rate of evaporation will slow down.

Looking for a Gas

Gases are everywhere. You may have heard about the atmosphere. The atmosphere is an envelope of gases that surrounds the Earth. In solids, atoms and molecules are compact and close together. Liquids have atoms that are spread out a little more. The molecules in gases are really spread out, full of energy, and constantly moving around in random ways.

What is another physical characteristic of gases? Gases can fill a container of any size or shape. It doesn't matter how big the container is. The molecules spread out to fill the whole space equally. Think about a balloon. No matter what shape you make the balloon, it will be evenly filled with the gas molecules. Even if you make a balloon animal, the molecules are spread equally throughout the entire shape.

Liquids can only fill the bottom of a container, while gases can fill it entirely. The shape of liquids is very dependent on gravity, while less dense gases are light enough to have a more freedom to move.

Gas or Vapor?

You might hear the term "vapor." Vapor and gas mean the same thing. The word vapor is used to describe gases that are usually liquids at room temperature. Good examples of these types of liquids include water (H2O) and mercury (Hg). They get the vapor title when they are in a gaseous phase. You will probably hear the term “water vapor” which means water in a gas state. Compounds such as carbon dioxide (CO2) are usually gases at room temperature. Scientists will rarely talk about carbon dioxide vapor.

Compressing Gases

Gases hold huge amounts of energy and their molecules are spread out as much as possible. When compared to solids or liquids, those spread out gaseous systems can be compressed with very little effort. Scientists and engineers use that physical trait all of the time. Combinations of increased pressure and decreased temperature force gases into containers that we use every day.

You might have compressed air in a spray bottle or feel the carbon dioxide rush out of a can of soda. Those are both examples of gas forced into a smaller space at greater pressure. As soon as the gas is introduced to an environment with a lower pressure, it rushes out of the container. The gas molecules move from an area of high pressure to one of low pressure.

Plasma Basics

Plasmas are a lot like gases, but the atoms are different, because they are made up of free electrons and ions of an element such as neon (Ne). You don't find naturally occurring plasmas too often when you walk around. They aren't things that happen regularly on Earth.

If you have ever heard of the Northern Lights or ball lightning, you might know that those are types of plasmas. It takes a very special environment to keep plasmas going. They are different and unique from the other states of matter. Plasma is different from a gas, because it is made up of groups of positively and negatively charged particles. In neon gas, the electrons are all bound to the nucleus. In neon plasma, the electrons are free to move around the system.

Finding a Plasma

While natural plasmas aren't found around you that often, man-made plasmas are everywhere. Think about fluorescent light bulbs. They are not like regular light bulbs. Inside the long tube is a gas. Electricity flows through the tube when the light is turned on. The electricity acts as an energy source and charges up the gas. This charging and exciting of the atoms creates glowing plasma inside the bulb. The electricity helps to strip the gas molecules of their electrons.

Another example of plasma is a neon sign. Just like a fluorescent lights, neon signs are glass tubes filled with gas. When the light is turned on, the electricity flows through the tube. The electricity charges the gas and creates plasma inside of the tube. The plasma glows a special color depending on what kind of gas is inside. Inert gases are usually used in signs to create different colors. Noble gases such as helium (He), Neon (Ne), Argon (Ar), and Xenon (Xe) are all used in signs.

You also see plasma when you look at stars. Stars are big balls of gases at really high temperatures. The high temperatures charge up the atoms and create plasma. Stars are a good example of how the temperature of plasmas can be very different. Fluorescent lights are cold compared to really hot stars. However, they are still both forms of plasma, even with the different physical characteristics.

Bose-Einstein Basics

The Bose-Einstein state of matter was the only one created while your parents were alive. In 1995, two scientists, Cornell and Weiman, finally created the condensate. When you hear the word condensate, think about condensation and the way gas molecules come together and condense and to a liquid. The molecules get denser or packed closer together.

Two other scientists, Satyendra Bose and Albert Einstein, had predicted it in the 1920s, but they didn't have the equipment and facilities to make it happen at that time. Now we do. If plasmas are super hot and super excited atoms, the atoms in a Bose-Einstein condensate (BEC) are total opposites. They are super unexcited and super cold atoms.

About Condensation

Let's explain condensation first. Condensation happens when several gasmolecules come together and form a liquid. It all happens because of aloss of energy. Gases are really excited atoms. When they lose energy, they slow down and begin to collect. They can collect into one drop. Water (H2O) vapor in the form of steam condenses on the lid of your pot when you boil water. It cools on the metal and becomes a liquid again. You would then have a condensate.

The BEC happens at super low temperatures. We have talked about temperature scales and Kelvin. At zero Kelvin (absolute zero) all molecular motion stops. Scientists have figured out a way to get a temperature only a few billionths of a degree above absolute zero. When temperatures get that low, you can create a BEC with a few special elements. Cornell and Weiman did it with rubidium (Rb).

Let the Clumping Begin

So, it's cold. A cold ice cube is still a solid. When you get to a temperature near absolute zero, something special happens. Atoms begin to clump. The whole process happens at temperatures within a few billionths of a degree, so you won't see this at home. When the temperature becomes that low, the atomic parts can't move at all. They lose almost all of their energy.

Since there is no more energy to transfer (as in solids or liquids), all of the atoms have exactly the same levels, like twins. The result of this clumping is the BEC. The group of rubidium atoms sits in the same place, creating a "super atom." There are no longer thousands of separate atoms. They all take on the same qualities and, for our purposes, become one blob.

Mixture Basics

Mixtures are absolutely everywhere you look. Most things in nature are mixtures. Look at rocks, the ocean, or even the atmosphere. They are all mixtures, and mixtures are about physical properties, not chemical ones. That statement means the individual molecules enjoy being near each other, but their fundamental chemical structure does not change when they enter the mixture. If the chemical structure changed, it would be called areaction.

When you see distilled water (H2O), it's a pure substance. That means that there are only water molecules in the liquid. A mixture would be a glass of water with other things dissolved inside, maybe one of those powders you take if you get sick. Each of the substances in that glass keeps its own chemical properties. So, if you have some dissolved substances in water, you can boil off the water and still have those dissolved substances left over. If you have some salt (NaCl) in water and then boil off the water, the salt remains in the pan. The salt is left because it takes very high temperatures to melt salt (even more to boil it).

Mixtures are Everywhere

There are an infinite number of mixtures. Anything you can combine is a mixture. Think of everything you eat. Just think about how many cakes there are. Each of those cakes is made up of a different mixture of ingredients. Even the wood in your pencil is considered a mixture. There is the basic cellulose of the wood, but there are also thousands of other compounds in that pencil.Solutions are also mixtures, but all of the molecules are evenly spread out through the system. They are calledhomogenous mixtures.

If you put sand into a glass of water, it is considered to be a mixture. You can always tell a mixture, because each of the substances can be separated from the group in different physical ways. You can always get the sand out of the water by filtering the water away. If you were busy, you could just leave the sand and water mixture alone for a few minutes. Sometimes mixtures separate on their own. When you come back, you will find that all of the sand has sunk to the bottom. Gravity was helping you with the separation. Don't forget that a mixture can also be made of two liquids. Even something as simple as oil and water is a mixture.

Alloys

There are a few more words you might hear when people talk about mixtures. We can't cover all of them, but we'll give you a quick overview of the biggies.Alloys are basically a mixture of two or more metals. Don't forget that there are many elements on the periodic table. Elements like calcium (Ca) andpotassium (K) are considered metals. Of course, there are also metals like silver (Ag) and gold (Au). You can also have alloys that include small amounts of non-metallic elements like carbon (C). Metals are the key thing to remember for alloys.

The main idea with alloys is that the combinations work better together than any of the metals do alone. Metallurgists (people who work with metals) sometimes add chromium (Cr) and/or nickel (Ni) to steel. While steel is already an alloy that is a very strong metal, the addition of small amounts of the other metals help steel resist rusting. Depending on what element is added, you could create Stainless Steel or Galvanized Steel. It's always about improving specific qualities of the original. Another good example of an alloy happens when metallurgists add carbon to steel. A tiny amount of carbon (a non-metallic element) makes steel stronger. These special carbon-steel alloys are used in armor plating and weapons.

Amalgams

Amalgams are a special type of alloy. We like them because we think mercury(Hg) is a cool element. You might know mercury as "quicksilver" or the metal that is liquid at room temperature. Anyway, amalgams are alloys that combine mercury and other metals in the periodic table. The most obvious place you may have seen amalgams is in old dental work. The fillings in the mouths of your grandparents may have been amalgams. We already talked about mercury being a liquid at room temperature. That physical trait was an advantage when they made fillings. Let's say you have an amalgam of mercury and silver (Ag). When it is created, it is very soft. As time passes, the mercury leaves the amalgam and the silver remains. The silver left over is very hard. Voila! You have a filling!

NOTE: Never, ever, play with mercury! It is very poisonous. You shouldn't even touch it, because it will seep into your skin. Dentists don't usually use amalgams with mercury anymore, because some scientists think the mercury can get people sick. When there was extra mercury left in the fillings, it could seep into the blood stream. Most of you will never even have silver fillings. Many dentists use resin fillings, which are made up of plastic and very fine particles of glass.

Emulsions

Let's finish up with a little information on emulsions. These special colloids(another type of mixture) have a mixture of oils and waters. Think about a bottle of salad dressing. Before you mix it, there are two separate layers of liquids. When you shake the bottle, you create an emulsion. As time passes, the oil and water will separate, because emulsions are mixtures.

Solutions and Mixtures

Before we dive into solutions, let's separate solutions from other types ofmixtures. Solutions are groups of molecules that are mixed and evenly distributed in a system. Scientists say that solutions are homogenous systems. Everything in a solution is evenly spread out and thoroughly mixed.Heterogeneous mixtures have a little more of one thing (higher concentration) in one part of the system when compared to another.

Let's compare sugar in water (H2O) to sand in water. Sugar dissolves and is spread throughout the glass of water. The sand sinks to the bottom. The sugar-water is a homogenous mixture while the sand-water is a heterogeneous mixture. Both are mixtures, but only the sugar-water can also be called a solution.

Can anything be in a Solution?

Pretty much. Solutions can be solids dissolved in liquids. When you work with chemistry or even cook in your kitchen, you will usually be dissolving solids into liquids. Solutions can also be gases dissolved in liquids, such as carbonated water. There can also be gases in other gases and liquids in liquids. If you mix things up and they stay at an even distribution, it is a solution. You probably won't find people making solid-solid solutions. They usually start off as solid/gas/liquid-liquid solutions and then harden at room temperature. Alloys with all types of metals are good examples of solid solutions at room temperature.

Making Solutions

A simple solution is basically two substances that are evenly mixed together. One of them is called the solute and the other is the solvent. A solute is the substance to be dissolved (sugar). The solvent is the one doing the dissolving (water). As a rule of thumb, there is usually more solvent than solute. Be patient with the next sentence as we put it all together. The amount of solute that can be dissolved by the solvent is defined as solubility. That's a lot of "sol" words.

Colloids

Science has special names for everything. They also have names for the different types of homogenous mixtures. Solution is the general term used to describe homogenous mixtures with small particles. Colloids are solutions with bigger particles. Colloids are usually foggy or milky when you look at them. In fact, milk is an emulsified colloid.

You may also hear about colloids if you study soil. While milk is an organiccolloid, soils can be made up of inorganic colloids, such as clay.

Making Solutions

So, what happens? How do you make thatsolution? Mix the two liquids and stir. It's that simple. Science breaks it into three steps. When you read the steps, remember...

Solute=Sugar
Solvent=Water
System=Glass.

1. The solute is placed in the solventand the concentrated solute slowly breaks into pieces. If you start to stir the liquid, the mixing process happens much faster.

2. The molecules of the solvent begin to move out of the way and they make room for the molecules of the solute. Example: The water has to make room for the sugar molecules to spread out.

3. The solute and solvent interact with each other until the concentration of the two substances is equal throughout the system. The concentration of sugar in the water would be the same from a sample at the top, bottom, or middle of the glass.

Can Anything Change Solutions?

Sure. All sorts of things can change the concentrations of substances in solution. Scientists use the word solubility. Solubility is the ability of the solvent (water) to dissolve the solute (sugar). You may have already seen the effect of temperature in your classes. Usually when you heat up a solvent, it can dissolve more solid materials (sugar) and less gas (carbon dioxide). If your friend was mixing sugar and water, she would be able to dissolve a lot more sugar into hot water rather than cold.

Next on the list of factors is pressure. When you increase the surrounding pressure, you can usually dissolve more gases in the liquid. Think about your soda can. It is able to keep the fizz inside, because the contents of the can are under higher pressure. Think about a bottle of soda. The first time you open the bottle, a lot of bubbles come out. If you open and close it over a few hours, fewer and fewer bubbles will come out of the solution. When you opened the bottle the first time, you lost the high pressure that was keeping the carbon dioxide (CO2) gas in solution.

Last is the structure of the substances. Some things dissolve easier in one kind of substance as opposed to another. Sugar dissolves easily in water and oil does not. Water has a low solubility when it comes to oil. Since oil is not soluble in water, it will never truly dissolve. Oil and water is a mixture, not a solution. The two types of molecules (oil and water) are not evenly distributed in the system.

Mixtures Around You

Two classic examples of mixtures are concrete and salt water. If you live near the ocean, they surround you every day. Even if you're inland, you need to remember that your tap water also has many compounds inside, and they act the same way that salt does. Concrete is a mixture of lime (CaO), cement, water(H2O), sand, and other ground-up rocks and solids. All of these ingredients are mixed together. Workers then pour the concrete into a mold and the concrete turns into a solid (as the cement solidifies) with the separate pieces inside.

While the cement hardening might be a chemical reaction, the rocks and gravel are held in place by physical forces. They are included in the mixture to increase the strength of concrete. The rocks and gravel are not chemically bonded to the cement. The gravel is also not evenly distributed. There are pieces of gravel here and there. You may have watched building construction before. They mix the concrete for hours to try and get all the little bits mixed evenly. Even with all that mixing, the concentrations of gravel still change from area to area.

Salt water is different. First, it's a liquid. Second, it's an ionic solution. Salt molecules separate into sodium (Na+) and chloride (Cl-) ions in the water.

You might be wondering why concrete and salt water are not new compounds when they are mixed together. The special trait of mixtures is that physical forces can still remove the basic parts. You can take the solid concrete and grind it up again. The crushed concrete can then be used as aggregate with new Portland cement. You might also sandblast concrete with decorative aggregate stones to reveal the stones trapped in the concrete. Salt water is even easier. All you have to do is boil the water off and the salt remains. It is as if you never mixed the two compounds. If the salt and water had reacted chemically, a new compound would have been created.

The thing to remember about mixtures is that you start with some pieces, combine them, and then you can do something to pull those pieces apart again. You wind up with the same molecules (in the same amounts) that you started with. The way you separate the molecules is as unique as the mixture. We have talked about grinding and boiling. If you have a mixture of salt and tiny pieces of iron (Fe), you can use a magnet to separate the iron from the mixture. Remember that gravity will help you separate both sand and oil from water if you wait a few minutes.