Matter is the Stuff Around You
Matter is everything around you. Matter is anything made of atoms
and molecules. 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 only find it in a few forms. As of 1995,
scientists have identified five physical states of matter. Each of
those states is sometimes called a phase. They may even discover
one more state by the time you get old.
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 noticed by William Crookes in 1879. The scientists who worked with the BoseEinstein condensate received a Nobel Prize for their work in 1995. But 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 all fluidy at room temperature. Gases are there, but you usually smell them before
you can see them. You don't see them because their molecules are really far apart. The BEC is all
about molecules that are really close to each other (even closer than atoms in a solid).
Changing States of Matter
Elements and compounds can move from one physical state to
another and not change their basic atomic parts. Oxygen (O2) as a
gas still has the same 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 just add a second oxygen atom, you would have hydrogen
peroxide (H2O2). The molecules in your glass would not be water anymore. A chemical change
happens when the atoms in a molecule are moved around or when atoms are added or taken away.
Chemical changes happen when bonds between atoms are created or destroyed. A physical
change of matter is about changing densities, pressures, temperatures, and other physical
properties. The basic chemical structure does not change when there is a physical change.
Physical Science 2013-2014
Binder Section: Notes/Vocab
States of Matter
There are five main states of matter. Solids, liquids, gases, plasmas, and Bose-Einstein condensates
(BEC) are all different states of matter. Each of these states is also known as a phase. Elements and
compounds can move from one phase to another when specific physical conditions are present. One
example is temperature. When the temperature of a system goes up, the matter in the system
becomes more excited and active. Scientists say that it moves to a higher energy state. Generally, as
the temperature rises, matter moves to a more active state.
Think about it this way. Remember that glass of water (H 2O) we talked about? When the temperature
of the water goes up, the molecules get more excited and bounce a lot more. If you give a liquid water
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 gas molecules.
A "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.
A compound or element can move from one phase to another, but still be the same substance. You
can see water vapor, in the form of steam, over a boiling pot of water. That vapor (or gas) can
condense and become a drop of water. If you put that drop in the freezer, it would become a solid
piece of ice. No matter what phase it was in, it was always water. It always had the same chemical
properties. On the other hand, a chemical change would change the way the water acted, eventually
making it not water, but something completely different. If you added a carbon (C) atom to a water
molecule, you would have formaldehyde (H2CO), and that is nothing like water.
Physical Science 2013-2014
Binder Section: Notes/Vocab
Solid Basics
So, what is a solid? Solids are usually hard, because their
molecules have been 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. Solids
can be hard, soft, big or small like grains of sand. The key
is that the 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. Even when you grind up a solid into a powder, you will see tiny pieces of
that solid under a microscope. Liquids will flow and fill up any shape of container.
Solids like their shape.
In the same way that a solid holds its shape, the atoms inside of a solid are not
allowed to move around too much. This is one of the physical characteristics of
solids. Atoms and molecules in liquids and gases 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 spin and the electrons fly around, but the
entire atom will not change position. Solids can be made up of many things. They can have pure
elements or a variety of compounds inside. When you get more than one type of compound in a solid
it is called a mixture. Most rocks are mixtures of many different compounds. Concrete is a good
example of a man-made mixture.
Crystals
On the other end of the spectrum from a mixture is something called a crystal.
When a solid is made up of a pure substance and forms slowly, it can become a
crystal. Not all pure substances form crystals, because it is a very delicate
process. The atoms are arranged in a regular repeating pattern called a crystal
lattice. A crystal lattice is a very exact organization of atoms. A good example is
carbon (C). A diamond is a perfect crystal lattice of carbon, while the graphite
arrangement of carbon atoms is a more random and disorganized. You can find
graphite in your pencils. For carbon, those two different structures (crystal lattice
vs. random arrangement) are called allotropes.
Physical Science 2013-2014
Binder Section: Notes/Vocab
Liquid Basics
The second state of matter we will discuss is a liquid. Solids are
things you can hold that maintain their shape. Gases are floating
around you or trapped in bubbles. What is a liquid? Water is a
liquid. Your blood is a liquid. Liquids are an in-between state of
matter. They can be found between the solid and gas states. They
don't have to be made up of the same molecules. If you have a
variety of materials dissolved in a liquid, it is called a solution.
One characteristic of a liquid is that it will fill up the shape of a
container. If you pour some water (H2O) in a cup, it will fill up the
bottom of the cup first and then fill the rest. The water will also take
the shape of the cup. The top part of a liquid will usually have a flat
surface. That flat surface is the result of gravity pulling on the
molecules. Putting an ice cube (solid) into a cup will leave you with
a cube in the middle of the cup because it is a solid. The shape of
the solid cube won't change until the ice becomes a liquid.
Another characteristic of a liquid is that it is difficult to compress.
When you compress something, you measure out a certain
amount of material and force it into a smaller space. Solids are
very difficult to compress and gases are very easy. Liquids are in
the middle, but tend to be difficult. When you compress something,
you force the atoms closer together. When the pressure goes up, substances are compressed.
Liquids already have their atoms close together, so they are hard to compress. Many shock
absorbers in cars compress liquids in sealed tubes.
Molecules Sticking Together
A special force keeps liquids together. Those intermolecular forces make sure that the molecules of
the liquid stick to each other. Solids are stuck together and you have to force them apart. Gases
bounce everywhere and they try to spread themselves out. Liquids actually want to stick together.
There will always be the occasional evaporation, where extra energy gets a molecule excited and the
molecule leaves the system. Overall, liquids have cohesive (sticky) forces at work to hold the
molecules together.
Physical Science 2013-2014
Binder Section: Notes/Vocab
Evaporation of Liquids
Sometimes a liquid can be sitting in one place (maybe a puddle)
and its molecules will become a gas. The process of a liquid
changing to a gas is 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... Bam! 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.
Physical Science 2013-2014
Binder Section: Notes/Vocab
Looking for a Gas
Gas is everywhere. There is something called the atmosphere.
That's a big layer of gas that surrounds the Earth. Gases are
random groups of atoms. In solids, atoms and molecules are
compact and close together. Liquids have atoms that are spread
out a little more. Gases are really spread out and the atoms and
molecules are full of energy. They are bouncing around constantly.
Gases can fill a container of any size or shape. It doesn't even
matter how big the container is. The molecules still spread out to
fill the whole space equally. That is one of their physical
characteristics. Think about a balloon. No matter what shape you
make the balloon, it will be evenly filled with the gas molecules.
The molecules are spread equally throughout the entire balloon.
Liquids can only fill the bottom of the container, while gases can fill
it entirely. The shape of liquids is really dependent on the force of
gravity, while gases are light enough to have a little more freedom
to move.
You might hear the term "vapor." Vapor and gas mean the same
thing. The word vapor is used to describe gases that are usually
found as liquids. Good examples are water (H2O) or mercury (Hg).
Compounds like carbon dioxide (CO2) are usually gases at room
temperature, so scientists will rarely talk about carbon dioxide
vapor. Water and mercury are liquids at room temperature, so they
get the vapor title when they are in a gaseous phase.
Compressing Gases
Gases hold huge amounts of energy, and their molecules are spread out as much as possible. With
very little pressure, when compared to liquids and solids, those molecules can be compressed. It
happens all of the time. Combinations of pressure and decreasing temperature force gases into tubes
that we use every day. You might see 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 than it would want,
and the gas escapes the first chance it gets. The gas molecules move from an area of high pressure
to one of low pressure.
Physical Science 2013-2014
Binder Section: Notes/Vocab
Changing States of Matter
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. 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? You could increase the pressure
to push those molecules together. The opposite works too. If you have a liquid at room temperature
and you wanted a gas you could use a combination of high temperatures and low pressures to solve
your problem.
Phase changes happen when certain points are reached. Sometimes a liquid wants to become a
solid. Scientists use something called a freezing point to measure the temperature at which a liquid
turns into a solid. There are physical effects that can change the freezing point. Pressure is one of
those effects. When the pressure surrounding a substance goes up, the freezing point and other
special points also go up. That means it's easier to keep things solid at higher pressures. Just
remember that there are some exceptions. Water (H2O) is special on many levels. It has more space
between its molecules when it is frozen. There's a whole expanding effect when the molecules
organize into a solid state. Generally, when temperatures get colder, solids shrink in size. They
become more dense.
CHEMISTRY TERM
Fusion (melting)
Freezing
Vaporization (boiling)
Condensation
Sublimation
Deposition
PHASE CHANGE
Solid to Liquid
Liquid to Solid
Liquid to Gas
Gas to Liquid
Solid to Gas
Gas to Solid
Solid to Liquid and Back to Solid
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. The atoms in a liquid have more energy
than the atoms in a solid. The easiest energy to find is probably heat.
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 has to be a little over zero
degrees Celsius (0oC). If you were salt, sugar, or wood, your melting
point would be higher than that of water. How do you know that? If their
melting points were lower, they would be liquids at room temperature.
Physical Science 2013-2014
Binder Section: Notes/Vocab
The reverse of the melting process is called freezing. Liquid water freezes and becomes solid ice
when the molecules lose a lot of energy.
Solid to Gas and 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, it just turns into a
gas. Have you ever heard of liquid carbon dioxide? It can be made, but not in normal situations. Can
you go from a gas to a solid? Sure. It's called deposition 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 becomes a solid.
Liquid to Gas and Back to Liquid
When you are a liquid and want to become a gas, you need to find a lot of energy. Once you can start
to pump 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 and 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 of electrons from your atoms.
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. When the ions 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 comes time to become a gas again, just flip the
neon light switch off. Without the electricity 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.
Physical Science 2013-2014
Binder Section: Notes/Vocab
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.
Physical Science 2013-2014
Binder Section: Notes/Vocab
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 gas molecules come together
and form a liquid. It all happens because of a loss 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.
Physical Science 2013-2014
Binder Section: Notes/Vocab
Chemical vs. Physical Changes
It is important to understand the difference between chemical and
physical changes. The two types are based on studying chemical
reactions and states of matter. We admit that some changes are
obvious, but there are some basic ideas you should know.
Physical changes are about energy and states of matter.
Chemical changes happen on a molecular level when you have
two or more molecules that interact and create a new molecule or
two.
When you step on a can and crush it, you have forced a physical
change. The shape of the object has changed. It wasn't a change
in the state of matter, because the energy in the can did not
change. When you melt an ice cube (H2O), you have also forced a physical phase change by adding
energy. That example caused a change in the state of matter. You can cause physical changes with
forces like motion, temperature, and pressure.
Looking at Molecules
Chemical changes happen on a much smaller scale. While some
experiments show obvious chemical changes, such as a color
change, most chemical changes that happen between molecules
are not seen. When iron (Fe) rusts, you can see it happen over a
long period of time. The actual molecules have changed their
structure (the iron oxidized). 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 reactions (O2). The oxygen in the air reacts with the
sugar, and the chemical bonds are broken.
Some chemical changes are extremely small. They happen over a
series of steps. The result might have the same number of atoms, but it 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 structural isomers. Those isomers have atoms
bonded in different orders. Also, 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 you find in living things.
Physical Science 2013-2014
Binder Section: Notes/Vocab