Download Unit 8.1 Nuclear Chemistry - Review Radioactivity

Unit 8.1 Nuclear Chemistry Nuclear Reactions
State College Area School District
Teacher: Van Der Sluys
Review
• Atoms consist of electrons, protons and
neutrons
• Atoms of elements are distinguished by
the number of protons in the nucleus
(atomic number)
• Isotopes of an element have different
numbers of neutrons but the same
number of protons
Radioactivity
• Reactions involving the nucleus of atoms.
• Stable nuclides are not radioactive. Our
focus will be on the less common naturally
occurring and/or man-made isotopes that are
radioactive.
• Radioactivity results when an unstable
nucleus falls apart or decays into a more
stable nucleus by giving off particles or
radiation.
1
Nuclear Notation
• An atom can be represented by an atomic
symbol, where X is the symbol for the
element, Y is the mass number and Z is the
atomic number
Y
X
Z
• Nucleons are the particles that make up the
nucleus of an atom (protons and neutrons)
Subatomic Particles
• Alpha (4 2 α) particles are made up of two protons and
two neutrons, which is essentially the nucleus of a
helium atom (4 2He2+).
• Beta (β−) particles are electrons (0 -1e) coming from
the decay of an unstable nucleus.
• Positrons are the antiparticle of an electron and
therefore have the same mass as an electron but
have a positive charge (0+1e).
• Gamma particles are high energy particles of energy
(0 0 γ) or photons.
• Protons (11 p) have a mass of 1 amu and a positive
charge.
• Neutrons (1 0 n) have a mass of 1 amu and no charge.
Nuclear Particles – Atomic
Symbols
Name
alpha particle
beta particle
gamma particle
Notation
Symbol
He or 42 α
α
0
-1
e or β
0γ
βγ
n
n
H or 11 p
e or +10 β
p
β+
4
2
0
1
0
neutron
proton
positron
0
-1
1
1
0
+1
2
What Makes a Nucleus Stable
The chemist’s point of view
• There are two important forces that occur in
the nucleus of an atom.
– The repulsion of the positively charged protons
from one another.
– The attractive force called the “strong nuclear
force” which acts only at very short distances and
with certain combinations of protons and neutrons
ratios close to 1:1. The neutrons act as insulators
of the charge of the protons and prevent the
protons from feeling each others charge.
What Makes a Nucleus Stable
The nuclear physicist's point of view
Strong interaction
From Wikipedia, the free encyclopedia
Note: Don’t worry if you don’ t understand this,
I barely understand this language either!!!
The strong interaction or strong force is today understood to represent the interactions
between quarks and gluons as detailed by the theory of quantum chromodynamics (QCD). The
strong force is the fundamental force mediated by gluons, acting upon quarks, antiquarks, and
the gluons themselves. Although the strong force only acts upon elementary particles directly,
the force is observed between hadrons as the nuclear force. As has been shown by many
failed free quark searches, the elementary particles affected are unobservable directly. This
phenomenon is called confinement, a theory which allows only hadrons to be seen.
History
Before the 1970s, when protons and neutrons were thought to be fundamental particles, the
phrase "strong force" was what is today known as the nuclear force or the residual strong
force. What were being observed were the "residual" effects of the strong force, which act on
hadrons, both baryons and mesons. This force was postulated to overcome the electric
repulsion between protons in the nucleus, and for its strength (at short distances) it was dubbed
the "strong force". After the discovery of quarks, scientists realized that the force was actually
acting upon the quarks and gluons making up the protons, not the protons themselves. For
some time after this realization, the older notion was referred to as the residual strong force,
and the "new" strong interaction was called colour force.
3
Penetrating Power
• The penetrating abilities of the nuclear
particles depends up the size of the
particle, its energy and the density of
the material being penetrated. For a
given material, the order of penetrating
ability is
α < β- = β+ < γ
Shielding
• Certain materials are used as
“shielding” because radio-particles do
not penetrate them very well. These
are usually very dense materials like
lead or concrete.
Types of Radioactive Decay
• Various radio-particles are given off by
radioactive isotopes when the break apart to
form more stable nuclei. The types of decay
include:
–
–
–
–
Alpha (α) emission 23892U --> 23490Th + 42He
Beta (β−) emission 9943Tc --> 9944Ru + 0-1e
Gamma (γ) emission
11 C --> 11 B + 0 e
Positron (β +) emission
6
5
+1
– Electron capture
4
Nuclear Equations
• The basic principle in writing nuclear
reactions
The two sides of a nuclear reaction must
have equal atomic numbers and atomic
mass numbers.
222 Rn
86
--> 21884Po + 42He
What is the missing particle?
238 U
92
37
--> 23490Th + YZX
20Ca
Y X
Z
--> YZX + 0+1e
--> 13154Xe + 0-1e
222 Rn
86
--> YZX + 42He
5
Natural Versus Induced Decay
• Natural decay results which an unstable
nuclei disintegrates
99
43Tc
--> 9944Ru + 0-1e
• Induced decay occurs when two particles are
collided together in a nuclear reactor or particle
accelerator
4 He
2
+ 147N --> 178O + 11H
Radioactive
Decay
Sequence
for U-238
http://www.ccnr.org/decay_U238.html
6
Summary
• Nuclear Particles
α or alpha particles
β- or beta particles
β+ or positrons
γ or gamma particles
• Nuclear decay reactions
Natural
Induced
7