Unit 10: Atoms and Periodicity
An atom is the smallest particle in which matter can be divided and still be
the same substance. The same type of atoms are elements. Elements can be
chemically combined to form compounds.
The atom was first seen in 1981 with the invention of the scanning
tunneling microscope, but atomic theory
(the ideas of the existence of atoms) has been around for over 2000 years!
Democritus (440 BC)-Greek Philosopher
Came up with the idea of the atom
He thought that if you were to cut up a material
you would eventually come to a piece that is
"uncuttable". He named this particle atom,
which comes from the Greek word atomos for
"indivisible"
John Dalton ( late 1700s)-- English School teacher
Developed the 3-part atomic theory based on his observations and published it in 1
His theory states:
1)All substances are made of matter
2)Atoms of the same element are exactly alike*, atoms of different elements are
different.
3)Atoms join with other atoms to make new substances--______________
The Dalton model of the atom
J.J. Thomson (1897)-His experiment used a Cathode Ray Tube to figure out what is inside the atom.
discovered the electron which shows that the atom is, in fact, divisible. There are
smaller particles within the atom itself.
http://my.hrw.com/sh/hp1/0030724929/student/ch11/sec01/qc02/hp111_01_q02fs.htm
An atom has NO overall charge if it contains the same number of
protons and electrons.
http://www.youtube.com/watch?v=eO2Z_2d9UJc&feature=related&safety_mode=true&persist_safety_mode=1&safe
tive
What happened when the magnets were brought close to the tube?
What does that suggest about the particles that make up the ray?
http://www.youtube.com/watch?v=IdTxGJjA4Jw&safety_mode=true&persist_safety_mode=1&safe=active
In his model, the atom is a blob of positively charged material
with negatively charged bits of electrons embedded in it.
http://www.youtube.com/watch?v=JUJPyQtoB5E&safety_mode=true&persist_safety_mode=1&safe=active
Thomson's model
Thomson called this the "plum-pudding model". The bits of plum represents the
negative corpuscles (electrons).
This is like chocolate chip ice cream
Ernest Rutherford (1909-1911)-The Gold foil experiment
Discovers that the atom is mostly empty space with a small
dense and positively charged center called the nucleus. It is
many times smaller than the diameter of the atom. In this
model, the electrons move randomly around the nucleus
He discovers particles larger than electrons.
He discovered the nucleus by shooting alpha particles at a
piece of gold foil.
http://my.hrw.com/sh/hp1/0030724929/student/ch11/sec01/qc03/hp111_01_q03fs.htm
An alpha
Particle
+
+
Alpha particles are emitted during
radioactive decay, along with gamma rays.
Rutherford used them as postitively charged
bullets to fire at the gold foil.
In Rutherford's experiment, he used the
positively charge alpha particles and observed:
1. most of the particles passed straight through
the foil
2. some particles were slightly deflected
3. a few particles bounce back.
Rutherford proposes that atoms have a densely
packed, positively-charged center which is surrounded
by the negatively charged electrons.
http://www.youtube.com/watch?v=wzALbzTdnc8&feature=related&safety_mode=true&persist_safety_mo
safe=active
·How can we use indirect evidence to
figure how something is constructed or
works without directly seeing it?
·How did scientists build our understanding of
atoms?
·What is plum-pudding atomic model and what
evidence was used to refute it?
·What is the Rutherford atomic model and what
evidence is there to support it?
Niels Bohr (1913)-- suggested that electrons travel around
the nucleus in definite paths.
http://my.hrw.com/sh/hp1/0030724929/student/ch11/sec01/qc05/hp111_01_q05fs.htm
Atoms
Neutron
+
Proton
Electron
Hydrogen
Atoms
Neutron
+
Proton
Electron
Helium
Atoms
Neutron
+
Proton
Electron
Carbon
Atoms
Neutron
+
Proton
Electron
Oxygen
Eat your skittles, but do not
leave a mess.
The Electron Cloud Model
Our modern model of the atom suggests that
there are clouds of electrons surrounding the
nucleus and that the exact location of the
electron cannot be predicted.
http://my.hrw.com/sh/hp1/0030724929/student/ch11/sec01/qc07/hp111_01_q07fs.htm
Compare:
http://my.hrw.com/sh/hp1/0030724929/student/ch11/sec01/qc06/hp111_01_q06fs.htm
The Electron Cloud
Model