How Matter is Arranged in the
Universe (and on Earth)
Werner Heisneberg: German Physicist: When asked how one
could envision an atom, replied: “Don’t try”
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
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.
(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
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
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.
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.
One or more electrons are transferred from one atom to
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
Gain an Electron
means you end up with a negative charge.
Now it’s called a
generally form crystals
have high melting
points, and conduct electricity.
A common example is Table Salt.
In general, covalent compounds often have a lower melting
point than Ionic compounds.
A type of bond in which atoms share one or more electrons.
Many covalent compounds are NOT water soluble, and those
that are, do not usually conduct electricity
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
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
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
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)
Niels Bohr-Electron Orbits, called Quantum Theory(1913)
“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
Bohr wrote that electrons could only occupy certain
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