The Nature of Matter

The universe is filled with matter and energy.  In fact, Albert Einstein showed us that matter and energy are interchangeable when he wrote his famous E=Mc2.  Throughout history, scientists tried to determine the exact nature of matter.  At first, the debate considered one central question - Is there a smallest piece of matter?  The ancient Greeks had opposing thoughts:

Aristotle   (384 BC. - 322 BC) - Matter is continuous and everything can be described with 4 "elements" ... earth, water, fire, & air.

Leucipus and Democritus  (about 460 BC to about 370 BC) - An atom is the smallest piece of matter.  That is, if you take a piece of gold (for example) and cut it in half, and again in half, and again ... you would eventually reach the smallest piece of "gold".  This would be an atom.  If you split the atom up, it is no longer gold.  As it turned out, Democritus was right!
 

In nature, there exists 92 different elements (promethium is only found in space ... not the earth) composed of protons, neutrons and electrons. In modern times, man has made additional elements in the lab.  This can be summarized by examining the periodic table.  Many elements on the list have very familiar names - gold, silver, oxygen, sulfur, to name a few.  Some you may never have heard of before - hafnium, osmium or francium.  The elements on the periodic table are the building blocks of everything around us.

Click on the picture to enlarge.

More on the Elements

In grade school you learned that the center of the atom is the nucleus and contains almost all the mass of the atom.  It consists of protons and neutrons.  You also learned that electrons (which have a much lower mass than protons or neutrons) orbit the nucleus.  Protons have a positive electric charge, electrons have a negative electric charge, and neutrons have no electric charge at all.  The difference between elements on the periodic table is the number of protons each has in the nucleus.  This is the element's atomic number.  For example, if there are 26 protons in the nucleus, you have iron (Fe).

Ions

Atoms (when isolated) are electrically neutral.  That is, they have the same number of electrons as protons.  But some atoms easily lose electrons and some atoms easily take in extra electrons.  You learn all about this in a chemistry class when you discuss the "rules" that electrons are subject to.  If an atom loses an electron, it becomes positively charged (because # of protons > # of electrons).  If an atom accepts an additional electron it becomes negatively charged.  This is called an ion.  But in either case, the element hasn't changed on the periodic table.

Isotopes

It is also possible to alter the number of neutrons in the nucleus.  This doesn't change the element on the periodic table either.  If the number of neutrons changes in an atom, we are dealing with different isotopes of the same element. For example, there are 3 known isotopes for hydrogen:
 

Isotopes of Hydrogen

 
   Number of Protons Number of Neutrons
Normal Hydrogen 1 0
Deuterium 1 1
Tritium 1 2

Each element has several different isotopes, but most are unstable.  Unstable isotopes will undergo radioactive decay and change from one element to another.  The element carbon, for example, is known to have 10 isotopes, 8 of them radioactive.  Radioactive isotopes will stabilize themselves by undergoing nuclear reactions.  Some isotopes take a very short time to decay, other take extremely long time periods to become stable.  When they do, they give off heat and produce new elements.

Changing one element to another - Nuclear Reactions

It takes a nuclear reaction to change one element to another.  When this happens, the number of protons in the nucleus changes.  Nuclear fission occurs when a heavier nucleus breaks into two (or more) lighter nuclei (which happens naturally with radioactive elements). This also takes place in nuclear power plants (like Point Beach, Wisconsin).  Nuclear fusion is when lighter nuclei are forced together to form heavier nuclei.  Examples of this are the hydrogen bomb and reactions in the center of stars.  In all these examples, elements change their identity on the periodic table.

Chemical reactions

Although much less dramatic than nuclear reactions, chemical reactions are much more common in our lives. This takes place when atoms which are grouped in one way rearrange themselves in different ways.  You all know that water has the chemical symbol H2O.  This means a molecule of water is made up of 2 hydrogen atoms and one oxygen atom.  Any reaction where the atoms that make up water, for example, are taken apart or put together would be considered a chemical reaction.

For example:

Anytime you witness something burning, you are seeing a chemical reaction.  Combustion of fossil fuels involve atoms of carbon and hydrogen found in the fuel with the oxygen in the air.  For example, methane combines with oxygen in the air to make carbon dioxide, water vapor and heat (the fire you see).

CH4 + 2 O2   --->  CO2 + 2 H2O + heat

Note: In most cases, the burning of a fossil fuel usually releases carbon dioxide (CO2 - an important greenhouse gas) and water.

Chemical reactions like combustion (fire) are dramatic, but slower chemical reactions are taking place all around you and inside of you.  The rotting of a tree stump and the digestion of the food you eat are some examples.  In these examples, the reaction takes place and energy is released.  Some chemical reactions require energy to be put into the system to proceed.  The most common example is photosynthesis.  This is the process where sunlight provides the energy to make all plants "go".

What holds atoms together in groups?

There are two primary ways to make atoms stick together: ionic and covalent bonds!

Ionic Bonds - Since unlike electric charges attract each other, two atoms can be pulled together if one is a positive ion and the other is a negative ion.   Salt, NaCl,  is a common example.  In solution, Sodium (Na) acquires a positive electric charge because it losses an electron. Chlorine (Cl) becomes negatively charged because it will gain an extra electron.  These two ions  seek each other out and form salt.  Ionic bonds tend to be weak.

Covalent Bonds -  Without turning you into chemistry majors, let's just say that some elements become more stable when they "own" more electrons and other elements would prefer to give them away if possible.  This all has to do with the ways electrons in the outer orbits (called valence electrons) are stacked up.  That being said, two (or more) atoms can achieve this stability by "sharing" electrons.  Common examples are water (H2O) and diamond (where one carbon atom covalently bonds to 5 adjacent carbon atoms).  These bonds tend to be stronger than ionic bonds ... resulting in a more permanent atomic relationship.  One particularly strong bond occurs between silicon and oxygen ... forming an extremely stable compound called silica.  You will soon see that the crust of the earth contains lots of silicon and oxygen ... so you might expect the crust had lots of silica.  It does!

Some technical stuff

Element - a substance that can not be simplified by chemical or physical means (a common book definition).  From our discussion on chemical reactions, you should see that these are not nuclear reactions.  Atoms only change partners.  Also, you can not change an element by any physical means.  That is, you can not shake it, bake it, rattle it, pound it, wave a magnet over it and expect the element to change on the periodic table.  An element only changes to different elements in nuclear reactions.

In the crust (the uppermost layer of the earth), the most common elements are:

Oxygen      = 46.6%
Silicon        = 27.7%
Aluminum    = 8.1%
Iron             = 5.0%
Calcium       = 3.6%
Sodium        = 2.8%
Potassium    = 2.6%
Magnesium  = 2.1%
Other           = 1.5%

You can see that over 75% of the crust is comprised of 2 elements - oxygen and silicon.  Also over 98% of the crust is made from only 8 different elements.

Mineral - an element or combination of elements forming a specific chemical composition and regular arrangement of atoms (another book definition).  If you had taken a chemistry class, this definition sounds very much like the word compound.  But this is an earth science class and we can make the definition stick if we place some additional strict limitations on the word - mineral

A mineral must be: By this definition, quartz is considered a mineral but glass (which is made from quartz which is cooled quickly) is not considered a mineral because the chemical bonding in glass is extremely chaotic.

By this definition (and the restrictions you see above), we are have limited ourselves to about  4000 known minerals and about 40-50 new ones are found each year.  If interested, check this page to see all the different kinds of mineral there are.

Thought questions (not to be handed in)

Is gold a mineral?
Is water a mineral?
Is ice a mineral?
Is cubic zirconium a mineral?

Since there are so many minerals they are grouped in mineral classes based on the elements they contain

Silicates = the largest group   (containing Oxygen & Silicon)
Oxides  =  has oxygen but no silicon
Sulfides = contains sulfur
Sulfates = has SO4 in its structure
Halides  = salt groups
Carbonates = has CO3 in its structure

Valuable Minerals - Ores

If a mineral has commercial value it may be considered an ore.  An ore is usually a metal (gold, silver, etc.) but not always (sulfur, fluorite).

Rocks

Rock - an aggregate of one or more minerals.  It should be very clear that there must be lots of different kinds of rocks - too many to list!

There are only 91 natural elements which can form over 4000 minerals which can make ???? different rocks!

Think of:
elements = letters
minerals = words
rocks = sentences

The two rocks you will want to know are Granite and Basalt! (more on this later)

       

Granite                                           Basalt

ŠJim Mihal 2004, 2006 - all rights reserved