chapter19_NuclearChemistry - Radioactivity and Nuclear...

1
Chapter 19
Radioactivity and
Nuclear Chemistry

2
Comparison Of Chemical
and Nuclear Reactions

Nuclear Reactions
1
Elements may be
converted from one to
another.
2
Particles within the
nucleus, such as protons
and neutrons, are
involved in reactions.

Chemical Reactions
1
No new elements can be
produced, only new
chemical compounds.
2
Usually only the outer
most electrons participate
in reactions.

3
Comparison Of Chemical
and Nuclear Reactions

Nuclear Reactions
3
Release or absorb
immense amounts of
energy, typically 1000
times more.
4
Rates of reaction are
not influenced by
external factors.

Chemical Reactions
3
Release or absorb much
smaller amounts of
energy.
4
Rates of reaction depend
on factors such as
concentration, pressure,
temperature, and
catalysts.

4
The Nucleus

Remember that the nucleus is comprised of
the two nucleons : protons and neutrons.

The number of protons is the atomic number.

The number of protons and neutrons together
is effectively the mass of the atom.

5
The Nucleus
Terminology used in nuclear chemistry
.
1.
Nuclide refers to a nucleus with specific
numbers of protons and neutrons.
2.
Isotopes are nuclei that have the same
number of protons but different neutron
numbers.

Isotopes are the same element.

6
Radioactivity

Nuclides of many elements are unstable.
They decay spontaneously, emitting
subatomic particles and electromagnetic
radiation.

We refer to these nuclides as radioactive .

7
Neutron-Proton Ratios

Any element with more than one proton
(i.e., anything but hydrogen) will have
repulsions between the protons in the
nucleus.

A strong nuclear force (Nuclear binding
energy) helps keep the nucleus from flying
apart.

8
Neutron-Proton Ratios

Neutrons play a key role stabilizing the
nucleus.

Because they help attract other nucleons through
strong nuclear force.

They lack the repulsive forces associated with the
positive charges of protons.

Therefore, the ratio of neutrons to protons is an
important factor in determining nuclear stability.

Tro, Chemistry: A Molecular
Approach
9
Valley of Stability (Belt of Stability)
for Z = 1 ⇒ 20,
stable N/Z ≈ 1
for Z = 20 ⇒ 40,
stable N/Z approaches 1.25
for Z = 40 ⇒ 80,
stable N/Z approaches 1.5
for Z > 83,
there are no stable nuclei

10
Stable Nuclei

Nuclei above this belt (or
band, valley ) have too
many neutrons.

Some neutrons need to be
converted to protons for
the nuclei to be stable.

11
Stable Nuclei

Nuclei below the belt have
too many protons.

Some protons need to be
converted to neutrons for
the nuclei to be stable.

12
Stable Nuclei

There are no stable nuclei with an atomic
number greater than 83, regardless of their
neutron to proton ratio.

These nuclei tend to decay into smaller
nuclei.

13
Experimentally, it can be shown that
nuclei have a preference for even
numbers of protons and neutrons.

14
Neutron-Proton Ratio
and Nuclear Stability
