Download Intro to the Atom PPT

The Atom
Structure of the Atom
Atom Vocabulary
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Nucleus
Located in the center of the atom
Made up of protons and neutrons
Carries a positive charge
Makes up nearly the entire mass of the atom.
Protons
Located within the nucleus
Have a positive charge
Determine the atomic number of the atom
Neutrons
Located within the nucleus
Carry no charge (neutral)
Composed of a proton bound to an electron
Determines the atomic mass when their number is added to the number
of protons.
Electrons
Surround the nucleus
Carry a negative charge
Play a major role in determining the chemical properties of the atom
When taken from or added to the atom they cause the atom to carry a
charge
Scale of the Atom
Atomic Number
The total number of protons
Atomic Mass
Protons plus Neutrons = Atomic Mass
Electrons
The number of electrons will always be the same
as the number of protons in a neutral atom!
A.P.E M.A.N.
Atomic # = Protons = Electrons
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Atomic Mass
Atomic #
_________
#Neutrons
Isotope
A variety of an element that has a
different number of neutrons
Isotopes are just atoms of an element that have different
numbers of neutrons. Since all elements occur in more than one
variation, all atoms are isotopes. They don't become an isotope,
any more than an atom becomes an atom, they just are.
Ion
An atom that has gained or lost electrons and carries
a charge
Quarks
The fractionally charged
particles that protons and
neutrons are made of.
Strong Nuclear Force
The strong nuclear
force is the force
that binds the
positively charged
protons together in
the nucleus. The
force is caused by
an exchange of
particles called
gluons.
String Theory
Recent research suggests that all atomic particles are
fundamentally composed of vibrating strings. The way in
which the string vibrates determines the properties of the
particle.
Video: Atomic Structure
Video: Quantum Theory
Radioactivity
Alpha Decay
Alpha decay occurs is because the nucleus has
too many protons which cause excessive repulsion.
In an attempt to reduce the repulsion, a Helium
nucleus is emitted.
Beta Decay
Beta decay occurs when the neutron to proton ratio
is too great in the nucleus and causes instability. In
basic beta decay, a neutron is turned into a proton
and an electron. The electron is then emitted.
Gamma Decay
Gamma decay occurs because the nucleus
is at too high an energy. The nucleus falls
down to a lower energy state and, in the
process, emits a high energy photon known
as a gamma particle.
Half-Life
The amount of time required for half the amount
of a radioactive substance to decay into a stable
daughter product
Video: Radioactive Decay
How did we get here?
http://www.youtube.com/watch?v=vUzTQWn-wfE
The Influence of Democritus
circa 460 B.C.E.
Teachings
• Was not the first to propose an atomic
theory. He was the first to write about it,
however.
• Formally developed the idea that matter
could not be divided infinitely and that
there must be some smallest particle
which he called “atomos” which means
indivisible.
• All matter is composed of atoms, which
are bits of matter too small to be seen.
These atoms CANNOT be further split
into smaller portions.
The Influence of Aristotle
circa 400 B.C.E.
Earth, Air, Fire, and Water
Aristotle’s Thoughts on the
composition of Matter
• According to Aristotle's theory all physical
objects in the world are composed of
earth, air, fire, and water in different
proportions. The varying amount of each
element in the composition accounts for
the infinite variety of things in the world.
• Although the idea of the atom never died,
Aristotle’s ideas were considered
authoritative until the early 1800’s.
Atomism and Aristotle
• The idea of the atom was strongly
opposed by Aristotle and others.
• Because of this, “atomism” faded into the
background.
John Dalton: The Father of
Modern Chemistry
1766-1844
Dalton’s Image of the Atom
Dalton’s Influence
• Unlike Democritus, Dalton based
his idea of the atom on
experimental evidence.
Dalton’s Atomic Theory
• All matter is composed of small particles
called atoms that are hard, solid, and
spherical.
• Atoms are the smallest particles that make
up matter. They cannot be divided,
created, or destroyed.
• The atoms of a specific element are
identical in size, mass, and all other
properties.
• The atoms of different elements differ in
size, mass, and other properties.
Cathode Ray Tube
In the Mid 1800’s is was discovered that when a current of
electricity passes through a glass tube a display of colorful
lights gradually appears as the gas inside it is evacuated.
Research with the tube gave evidence that charged rays of
some kind are traversing the tube. . These were called
cathode rays.
Cathode Ray Tube
Sir William Crookes
1832-1919
Crookes Tube
William Crookes, an English physicist, creates a greatly
improved version of the vacuum tube (the "Crookes
tube") and shows that cathode rays travel in straight lines,
cast sharp shadows, and carry an electric charge. He
even puts a little paddle wheel into one tube and shows
that the cathode rays can turn the wheel when they hit it,
just like a stream of water!
J.J. Thompson
1897
Using a modified Crookes Tube J.J. Thompson showed
that all cathode rays were the same, regardless of what
material the cathode was made of.
Based on the results of his
experiments he concluded that
the cathode rays were a stream
of small, electrically charged
particles which have a mass over
a thousand times less than that of
an atom. Thomson had
discovered the electron.
The Plum Pudding Model
Thompson developed the first basic modern model of the
atom. His model was called the “plum pudding" model, since
it resembled plum pudding, which is a dessert common in
England. Thompson's model featured the negatively
charged electrons randomly "stuck" into a ball of positively
charged matter.
Ernest Rutherford
1906
The Gold Foil Experiment
Rutherford and his students pass a beam of alpha particles
through paper thin gold foil. The expectation was that the
particles would pass straight through since the atom was thought
to have its differently charged particles spread evenly throughout
as represented by Thompson’s plum pudding model.
Top: Expected results of Rutherford's gold foil experiment: alpha
particles passing through the plum pudding model of the atom
undisturbed.
Bottom: Observed results: Some of the particles were deflected,
and some by very large angles. Rutherford concluded that the
positive charge of the atom must be concentrated into a very small
location: the atomic nucleus.
Rutherford’s Solar System Model
of the Atom
Rutherford pictured the atom as having a massive, positively
charged nucleus that was surrounded by orbiting electrons at a
great distance. The atom was mostly empty space!
Niels Bohr
1922
Electron Energy Levels
Bohr and Electron Energy Levels
• The electron travels in a circular path around the
nucleus. This path is called an orbit.
• At normal living conditions, room temperature, the
electron resides in the orbit which is closest to the
nucleus. This is the position of lowest energy content
for the electron.
• If energy is added to an electron, the electron will move
to a new orbit. This orbit will be farther from the
nucleus, and is a position of higher energy content.
This new position is known as an excited state.
• When an electron moves from one orbit to another orbit,
it does so without ever passing through the space
between the orbits. Known as a quantum jump.
• When an electron is in an excited state, it will always
drop down to a lower energy state, ultimately returning
to ground state.
Electron Transition
If an electron moves from a low energy
level to a higher energy level it does so by
gaining energy. If it moves from a higher
energy level to a lower energy level, it does
so by releasing energy. The released
energy is in the form of electromagnetic
radiation. This transition is known as a
quantum leap.
Bohr Model
Erwin Schrodinger
1930
Viewed electrons as
continuous clouds
and introduced
"wave mechanics"
as a mathematical
model of the atom.
James Chadwick
1932
Using alpha particles
discovered a neutral
atomic particle with a
mass close to a proton.
Thus was discovered
the neutron.