Download Atoms and Elements

Atoms and Elements
Mr. Olsen
7th Grade
Integrated Science
Paper Clip Demonstration
Take a pile of paper clips (all of the same size and
color).
Divide the pile into two equal piles.
Divide each of the smaller piles into two equal piles.
Repeat step 3 until you are down to a pile containing only one
paper clip. That one paper clip still does the job of a paper clip
(i.e., hold loose papers together).
Now, take a pair of scissors and cut that one paper clip in half.
Can half of the paper clip do the same job as the single paper
clip?
The Indivisible Atom
If you do the same thing with any element,
you will reach an indivisible part that has the
same properties of the element, like the
single paper clip. This indivisible part is
called an atom.
Atoms
The word atom is derived from the Greek
word atom which means indivisible. The
Greeks concluded that matter could be
broken down into particles to small to be
seen. These particles were called atoms
Atomic Ideas
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The idea of the atom was first devised by
Democritus in 530 B.C. In 1808, an
English school teacher and scientist
named John Dalton proposed the modern
atomic theory. Modern atomic theory
simply states the following:
Atomic Theory
Every element is made of atoms - piles of paper clips.
All atoms of any element are the same - all the paper clips in the pile are the same
size and color.
Atoms of different elements are different (size, properties) – like different sizes and
colors of paper clips.
Atoms of different elements can combine to form compounds - you can link different
sizes and colors of paper clips together to make new structures.
In chemical reactions, atoms are not made, destroyed, or changed - no new paper
clips appear, no paper clips get lost and no paper clips change from one size/color
to another.
In any compound, the numbers and kinds of atoms remain the same - the total
number and types of paper clips that you start with are the same as when you finish.
Atomic Models
Over time, the scientific
model of what an atom
looks like has evolved
beginning with
Democritus and his
“uncuttable” atom.
John Dalton (1803)
The Billiard Ball Model:
John Dalton viewed the atom as a small solid sphere. He
really got the "ball" rolling for modern chemistry!
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Each element was composed of the same kind of atoms.
Each element was composed of different kinds of atoms.
Compounds are composed of atoms in specific ratios.
Chemical reactions are rearrangements of atoms (mass
is conserved).
Joseph John Thompson (1897)
Plumb Pudding Model:
In 1903, J. J. Thomson proposed a subatomic model of the atom. The
model pictured a positively-charged atom containing negatively
charged electrons. Thomson visualized electrons in homogeneous
spheres of positive charge in a way that was analogous to raisins in
English plum pudding Thus, the Thomson proposal became popularly
know as the plum pudding model of the atom.
This model was not correct, but it was consistent with the evidence at
the time.
Ernest Rutherford
Solar System Model:
Ernest Rutherford discovered that the atom is mostly empty
space with a dense positively charged nucleus surrounded
by negative electrons. Rutherford received the Nobel Prize
in chemistry in 1908 for his contributions into the structure
of the atom. In 1913 Neils Bohr proposed that electrons
traveled in circular orbits and that only certain orbits were
allowed. This model of the atom helped explain the
emission spectrum of the hydrogen atom. He received the
Nobel Prize in physics in 1922 for his theory.
Solar System Model
The Bohr Model
1913, Bohr speculated that electrons orbit around
the atomic nucleus just as planets circle around
the Sun.
He suggested that the electron orbits were at a
fixed distance from the nucleus and had a definite
energy.
The electron was said to travel in a fixed-energy
orbit that was referred to as an energy level.
The Bohr Model
Current Model of the Atom
The Quantum-Mechanical Model:
According to this model of the atom, the positively charged
protons and the neutral neutrons are still located in the
nucleus of the atom.
The electrons, no longer thought of as locked into "fixed“
orbits, are collectively located in an area called the electron
cloud. These electrons, moving at extremely high speeds,
effectively occupy the entire area of the cloud.
Electron Cloud
Current Model of the Atom
Atoms and Matter
Atoms are the basic building blocks of
matter.
Resources
http://science.howstuffworks.com/atom1.htm
http://www.csmate.colostate.edu/cltw/cohorpages/viney/atomhistory.html
http://wind.cc.whecn.edu/~mechalke/chapter5/Chapter5.htm
http://www.fordhamprep.org/gcurran/sho/sho/lessons/lesson33.htm