Transcript Chemistry You Need to Know

Chapter 4: Glow in the Dark
Introductory Activity
List as many things as you can think of
that “glow”
What do you have to do to make these
“glowing” things “glow”?
Glow in the dark
This chapter will introduce the chemistry
needed to understand how glowing things
work
Section 4.1: History of Atomic Theory
Section 4.2: Atomic Structure
Section 4.3: Electron Structure
Section 4.4: Periodic table
Section 4.5: Periodicity
Section 4.6: Light
Section 4.7: Light and matter
Glow in the dark
Is based on
Electron
structure
Gives off
Changes in produce
Is a part of
Light
Which can
be determined using
Periodic
Table
Atomic
structure
Arranged to show
Is based on
Atomic
theory
Periodicity
Section 4.1—Development of
Atomic Theory
Dalton’s Atomic Theory
John Dalton’s theory based on experiments in early 1800’s
 All matter is made of tiny particles “atoms”
 Atoms cannot be created, divided, destroyed or
changed into other types of atoms
 Atoms of the same element have identical
properties
 Atoms of different elements have different
properties
 Atoms of different elements combine in wholenumber ratios to form compounds
 Chemical changes join, separate or rearrange
atoms in compounds
Cathode Ray Tubes
A cathode ray is a ray of light traveling in a vacuum (no other particles inside)
The ray travels from one metal plate to another as the plates are connected to
electricity
Cathode ray
Metal plate (cathode)
releases stream
Metal plate (anode) to
which stream travels
Cathode Ray Tubes & Charge
In the late 1800’s, JJ Thomson put charged plates outside the tube
Negatively charged plate
-
+
Positively charged plate
Ray is deflected
away from negative
plate and towards
positive plate
It made no difference what type of metal he used in the tube—all material produced
this stream that curved towards the positive charge
Thomson’s conclusions
 The evidence from Thomson’s work showed that
there was something negatively charged in
atoms
 Since all types of metal produced the same
result, the negative charge is in all types of
atoms
 Since atoms were overall neutral, if there was a
negative charge there had to also be a positive
charge
 In 1897, Thomson announced that the rays were
electrons and they had a negative charge
Theories change
 Thomson’s evidence showed Dalton’s idea of
solid, uniform atoms was incorrect.
 Eugene Goldstein conducted experiments to
label the positive part “protons” and determined
it has the same charge as the electron (with
opposite sign) but is 1837 times heavier!
 Thomson developed the “plum pudding” model.
Since most of us aren’t familiar with plum pudding, you
can think of it as a chocolate cookie dough theory
Thomson’s Theory
The “chips” are the negative
electrons.
The “dough” is the positive
portion
The “chips” are stationary and
don’t move within the “dough”
Remember, officially this theory
is called “plum pudding” but it’s
the same idea!
Gold Foil Experiment
Hans Geiger performed experiments in the
early 1900’s where he bombarded very
thin gold foil with radioactive particles
(alpha particles “”)
They expected these relatively heavy
particles to go through the atoms with a
small deflection
What happened in the experiment?

Gold foil
What did he see?
Most of the alpha particles passed straight
through with no deflection
These particles did not run into anything
Some did deflect slightly
These particles ran into something much
smaller than themselves
A few were reflected back the direction
they came from
These particles ran into something very dense
What did that mean?
Atoms are mostly empty space
Electrons (the smaller particles) were the
cause of the small deflections
There must be a small area of the atom
with most of its mass (the protons) that
caused the reflections.
He called this small, dense area the nucleus
A third particle
The protons and electrons could explain
the charges of the various parts of the
atom
They could not explain the total mass of
the atoms
Neutrons were proposed in 1920’s but not
confirmed until 1932 by James Chadwick
Neutrons had mass similar to protons and no
charge. They were located in the nucleus
More changes to the theory
Niels Bohr performed experiments with
hydrogen atoms & light
He determined that electrons are in levels
according to how much energy they have
and that only certain energy amounts were
allowed.
The Bohr Model
It consists of the nucleus with protons &
neutrons and electrons in concentric orbits
(circles) outside the nucleus
The circle closest to the nucleus contains
the lowest energy electrons
The first level can hold 2 electron, then the
next two levels can each hold 8 and then
levels farther out can hold 18.
Pictures of the Bohr Models
Electron
Proton
Neutron
Hydrogen-1
Helium-4
Lithium-6
Use of the Bohr Model now
We no longer believe electrons are in
concentric circles, but this is still a
convenient way to show energy levels on
2-dimensional paper
Modern Atomic Theory
In the 1920’s, Bohr’s research lead the
way for the study of quantum mechanics
(the study of tiny particles)
Modern atomic theory uses calculus
equations to show how the subatomic
particles act as both particles and waves
These equations show the most probable
location of electrons in the atom (known as
atomic orbitals)