The Mighty Atom
The Mighty Atom
How Matter is Arranged in the Universe (and on Earth)
An Overview
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Gluons--->Quarks--->Protons, Neutrons, Electrons-->Atoms-->Molecules-->Elements--->Compounds-->Mixtures, Solutions, Suspensions

Werner Heisneberg: German Physicist: When asked how one could envision an atom, replied: “Don’t try”


Atomic Structure


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.


Sub-atomic structure
(What makes up an atom?)
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 pointlike units known as quarks.
Each proton or neutron consists of three quarks.
 Massless particles called gluons hold the quarks together.



The Size of an Atom
The diameter of an atom ranges from about 0.1 to 0.5 nanometer.
A nanometer 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.
   

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.


Chemical Bonds
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.

    Ionic Bonds
One or more electrons are transferred from one atom to another.
  This addition or loss of an electron will affect the charge of the atom.
 Lose an Electron,
end up with a positive charge,
now the atom is called a
  Positive Ion. 
Gain an Electron
 means you end up with a negative charge.
        Now it’s called a Negative Ion.

        Ionic Compounds generally form crystals
        have high melting points, and conduct electricity.
A common example is Table Salt.

    Covalent Bonds
A type of bond in which atoms share one or more electrons.
           
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



History of Atomic Theory
(How do we know what we know?)

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.

Modern Atomic Theory is based upon the work of many
people, including the men listed below.

John Dalton- Atomic Structure (1803)
J.J. Thomson- Electrons(1897)
Ernest Rutherford-Nucleus(1911) 
Niels Bohr-Electron Orbits, called Quantum Theory(1913)
James Chadwick-Neutrons(1932)


Bohr: “A person who wasn’t outraged on first hearing about quantum theory didn’t understand what had been said”.  


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.




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