MS-PS1-1
The Mighty Atom
How Matter is Arranged in the Universe (and on Earth)

An Overview

Gluons--->Quarks--->Protons, Neutrons, Electrons-->Atoms-->Molecules-->Elements--->Compounds-->Mixtures, Solutions, Suspensions

Tiny as atoms are, they consist of even more minute particles.
The three basic types are protons, neutrons, and electrons.
Each atom has a definite number of these subatomic particles.
The protons and neutrons are crowded into the nucleus,
 an exceedingly tiny region at the center of the atom.

If a hydrogen atom were about 4 miles (6.4 kilometers) in diameter, its nucleus would be no bigger than a tennis ball.

The rest of an atom outside the nucleus is mostly empty space.
The electrons whirl through this space, completing billions of trips around the nucleus each millionth of a second.
The fantastic speed of the electrons makes atoms behave as if they were solid, much as the fast-moving blades of a fan prevent a pencil from being pushed through them.
Electrons are moving so quickly, they really CAN be in two places at once.

An atom is made up of particles called protons, neutrons, and electrons.
Protons and neutrons, which carry most of the atom's mass, are composed of point-like units known as quarks.
Protons and Neutrons are found in the nucleus.  Protons have a positive charge, neutrons have no charge (a neutral charger).
All those positively charged should repel one another, similar charges repel, opposites attract.
BUT, there's a force, called the Nuclear Force that holds the nucleus together. 
The third sub atomic particles are called Electrons, and they have a negative charge.
Electrons orbit the nucleus, just like planets orbit the sun.
The attraction between the negatively charged electrons, and the positively charged nucleus is what holds the atom together. 
This force holding the electrons near the nucleus is called the Electromagnetic Force.

The Protons (more specifically, the number of protons in an atoms nucleus) give an atom its properties.
The Neutrons balance out the Protons, allowing the atoms to be stable and long lasting.
The Electrons, specifically the outermost electrons, (called Valence Electrons) are used
to connect one atom to another in a process called "Bonding".

Most of the mass of an atom comes from the protons and neutrons.  Electrons are very, very small, and don't have much mass.

Think of this:  If atoms are mostly empty space, why don't you slip right through them when you sit in a chair?  If the chair is mostly
empty space, and YOU are mostly empty space, why is it you end up sitting on the chair, rather than passing through it
like a ghost?

The answer has to do with electric charges.

Similar Charges repel one another.  The outside of every atom has a negative charge, caused by the orbiting negatively
charge electrons.  When the negatively charged chair, meets your negatively charged butt, those two charges repel
one another.  You're not really sitting on a chair, you're sitting on a very thin "force field" produced by the
electrons repelling one another.

The diameter of an atom ranges from about 0.1 to 0.5 nano-meter.
A nano-meter is a billionth of a meter, or 1/25,400,000 inch.
Protons and neutrons make up the atom's nucleus, which is about ten thousand times smaller than the atom.
Electrons whirl around the nucleus. Generally, even with our best technology, actual atoms are just too small
to be seen.  However, recently, using our most powerful imaging devices, like the Electron Microscope, it's
become possible to actually see some of the larger atoms.

What keeps it all together?

Differences in electric charge hold the atom together.
Protons have a positive charge, and neutrons are electrically neutral, so the nucleus as a whole is positively charged.
Electrons are negatively charged.
Because opposite charges attract, an electric force tends to keep the electrons in place.
Electrons whirl around the nucleus in layers called electron shells.

How do atoms join together to form other things?

The electrons in the outermost shells (called valence electrons) are not tightly bound to the nucleus.
 As a result, some outer electrons can be shared by two atoms in a chemical bond, a linking of atoms.

Atoms that bond with one another can form what's called a Molecule.  Molecules can be made with the same type of atoms,
like two Oxygen atoms can bond together to form a molecule of O₂, which is the type of Oxygen that we can breathe.  Add one more
Oxygen atom and the molecule becomes Ozone (O₃), which is a useful gas here on Earth, but you can't breathe it to stay alive.  Only the
O₂ can do that!
Different Atoms can bond together as well.  For example, an atom of an explosive and reactive metal element called
Sodium (Na) can bond with an atom of a poisonous gas called Chlorine (Cl).  The new molecule is called
Sodium Chloride.  (NaCl).  Not only is it NOT deadly, but it's so common that you probably put some of this
stuff on your food every day.  Sodium Chloride is simple table salt.

When atoms bond together, the new molecules formed generally have very different properties than the "parent atoms" had.

Another term to know is Compound.  A compound is a molecule made with different atoms.  An example of a compound might be
H₂0 (two atoms of Hydrogen, one atom of Oxygen, bonded together)  this is the formula for Water.

One atom of Hydrogen, one atom of Chlorine forms (HCl) or Hydrochloric Acid.  This is the type of acid in
your stomach that helps to digest and break down the food you eat. 

H₂SO₄ is Sulfuric Acid (two atoms of Hydrogen, one atom of Sulfur, four atoms of Oxygen).  Sulfuric acid is in the
atmosphere of the planet mercury, where when it rains, it's droplets of acid, not water, that fall to the surface. 
Sulfuric Acid is found in a car's battery.



Not all electrons are the same distance from the nucleus.
The electrons that are the farthest away from the nucleus are called Valence Electrons.
Only Valence Electrons are involved in bonding.


In general, Covalent compounds often have a lower melting point than Ionic compounds.
 Many Covalent compounds are NOT water soluble, and those that are, do not usually conduct electricity

      Common Examples are Water, Butter, and Wax

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History of Atomic Theory

The idea that everything is made up of a few simple parts originated during the 400's B.C. in the philosophy of atomism.
Atomism was founded by the Greek philosopher Leucippus,
but his disciple Democritus developed the philosophy more fully.
Democritus gave his basic particle the name atom, which means uncuttable.
He imagined atoms as small, hard particles, all composed of the same substance but of different sizes and shapes

The birth of the modern atomic theory.
In 1750, Rudjer Boscovich, a scientist born in what is now Croatia,
suggested that Democritus might have been wrong in believing that atoms are "uncuttable."
Boscovich thought that atoms contain smaller parts,
which in turn contain still smaller parts,
and so forth down to the
fundamental building blocks of matter.
 He felt that these building blocks must be geometric points with no size at all.
Today, most atomic physicists accept a modern form of this idea.

Bohr’s contribution to our understandings about the structure and behavior of an atoms. 

The problem was in explaining how electrons could manage to keep flying around the nucleus without losing energy and crashing.
 Bohr wrote that electrons could only occupy certain well-defined orbits. 
According to his theory electrons moving between orbits would disappear from one and reappear instantaneously in another,
without visiting the space between. 
This idea was the famous “Quantum Leap”.
 Bohr won the 1922 Nobel Prize in physics for this dazzling insight.