INSIDE THE ATOM
Three Topics: Section 1
• How scientists model the atom
• What are charged particles
• What were Rutherford’s experiments
REVIEW VOCABULARY
Matter: anything that has mass and takes up space.
New Vocabulary
anode
•
electrode with a positive charge
electron cloud
•
region surrounding the nucleus in which electrons travel
cathode
•
electrode with a negative charge
neutron
•
particle in the nucleus of an atom that has the same mass as a
proton and is electrically neutral
alpha particle
•
fast-moving, positively charge bit of matter
proton
•
positively charged particle present in the nucleus of all atoms
•
negatively charged particle located outside the nucleus of an atom
•
matter made up of only one type of atom
electron
element
FIRST THOUGHTS
• Summarize early ideas about the structure of matter
• Matter was made of tiny particles and could be
cut into smaller and smaller pieces until reaching
a piece that could not be cut any more.
• This smallest piece is an atom.
Matter is
made up of
atoms
Atoms cannot
be divided into
smaller pieces
Dalton’s Ideas
About matter
All atoms of an
element are
exactly alike
Different
elements are
made of different
kinds of atoms
Crooke’s Tube
Mask
Cathode -
Shadow
Anode +
Crooke’s Experiments
• He connected a battery to cathode (-) and
anode (+) of a tube. He found that an object in
the middle of the tube (mask) cast a shadow in
a green glow. He concluded that the glow was
caused by rays, or streams of particles.
thomson’s experiments
Rays are bent by magnet
CATHODE RAYS
MAGNET
Thomson’s Experiments
• He placed a magnet next to the tube. The ray was
bent by the magnet, showing the ray was made of
particles, not light. He envisioned an atom as a sphere
of positive charge with negatively charged electrons
spread out evenly within. This is sometimes called The
Plum Pudding Model.
rutherford’s experiment
Rutherford’s Experiment
•
Experiment: Rutherford fired alpha particles at a thin film of gold.
A screen lit up when it was hit by a charged particle.
•
Expected Result: Almost all the alpha particles would go straight
through.
•
Actual Result: More particles bounced off than expected - some
of them straight back!
•
Conclusion: Positive and negative charges not evenly spread out.
Positive charge concentrated into a nucleus.
Describe the following improvements to atomic theory.
After Rutherford’s model, how
How electrons are thought to
the extra mass in the nucleus move in the most current atomic
was explained
model
Neutron - neutral charge
Electron Cloud
The Atom
Electrons
+
+
+
+
Nucleus
Protons
Neutrons
Electron
Cloud
The Atom
particle
location
charge
mass
(relative)
proton
nucleus
+
2000
neutron
nucleus
none
2000
electron
electron
cloud
--
1
Section 2: The Nucleus
• What is radioactive decay?
• What is half-life?
• How are radioactive isotopes used?
REVIEW VOCABULARY
Atom: Matter is made up of atoms.
New Vocabulary
atomic number
•
number of protons in nucleus
isotope
•
atom of an element with different number of neutrons
mass number
•
number of neutrons plus number of protons
radioactive decay
•
release of nuclear particles and energy
•
changing of one element into another through radioactive decay
•
high-energy electron that comes from the nucleus
•
amount of time it takes for half a sample of an element to decay
transmutation
beta particle
Section 2: The Nucleus
Carbon-12
Carbon-13
Carbon-14
Atomic number
6
6
6
Number of protons
6
6
6
Number of neutrons
6
7
8
Mass Number
12
13
14
Summarize what the strong nuclear force does.
It holds the protons and neutrons in the nucleus.
READING THE PERIODIC TABLE
carbon
Name
6
Atomic Number
= # of protons, # of electrons
C
Symbol
12
Atomic Mass
= # protons + # neutrons
Sequence steps of radioactive decay
The electron
Neutron
becomes
unstable
Neutron splits
into electron
and proton.
The proton
stays in the nucleus.
is
ejected with a large
amount of energy.
Atomic number
increases by one.
HALF-LIFE
• You have 100 grams of Iodine-131, which has a
half-life of 8 days. How much will be left after 24
days?
1
2
100 g
3
50 g
25 g
12.5 g
Begin
8 days
16 days
24 days
HALF-LIFE
• You have 16 grams of Element-X, which has a halflife of 10 days. How much will be left after 40 days?
16 g
Begin
1
8g
10 days
2
4g
20 days
3
2g
30 days
4
1g
40 days
HALF-LIFE
• You have 20 grams of Element-X, which has a halflife of 2 days. How much will be left after 6 days?
1
20g
2
10g
3
5g
2.5g
2 days 4 days 6 days
Rate of Decay
Time Elapsed
Mass
Start
1st
2nd
3rd
HalfLife HalfLife HalfLife
0 days
8 days 16 days 24 days
20 g
10 g
5g
2.5 g
half-life the amount of time it takes for one half of a
substance to decay.
Identify uses and hazards of radioactive material.
USES
Smoke detectors
Medicine
Date fossils
Energy
HAZARDS
Radiation
poisoning
Radioactive
Material
Long half-life