Download Chapter 25

Chapter 25 –
nuclear chemistry
1. What causes a transmutation of the nucleus to occur?
2. How are nuclear decay reaction equations balanced?
3. Do all radionuclides decay at the same rate?
Radioisotopes

Becquerel’s accidental discovery of transmutation and radioactivity.
– Transmutation – the conversion of an atom of one element to an atom of another
element

Marie Curie coined the term radioactivity.
– The process by which nuclei emit particles and rays.

Unstable nuclei decay at a constant rate – cannot be affected.
– In comparison to ____________ ________________.

Decay releases energy, and transforms the element into a more
stable and different element.
Unstable isotopes

Important – not all nuclei are radioactive!
Many are quite stable and do not decay.
Band of Stability
Many nuclei are stable
– their data is found on
the band of stability.
Unstable nuclei change
their nuclear structure
to move toward the
n0/p+ ratio of stable
nuclei on the band of
stability.
Transmutation processes*
Alpha (α)
 Beta (β)
 Gamma (γ)
 Positron (β+)
 Proton or neutron capture

* Gamma emission alone does not produce a new element.
Alpha decay
Nucleus releases a
particle made up of 2
p+ and 2 n0.
Large nuclei do this.
Rutherford used this
particle in his
experiment!
Which element
produced it?
222
88𝑅𝑎
→ 42𝐻𝑒 + 218
86𝑅𝑛
Beta decay
Nucleus converts a
neutron into a
proton and an
electron.
n0 → p+ and eProton stays behind,
electron (β particle)
is ejected from the
nucleus
14
6𝐶
→
14
7𝑁
+ −10𝑒
Gamma decay
High energy
radiation emitted
from the nucleus
Nuclear structure is
unchanged.
230
90𝑇ℎ
→
226
88𝑅𝑎
+ 42𝐻𝑒 + 𝛾
Positron decay
Nucleus converts a
proton into a
neutron and an
positively-charged
electron.
p+ → n0 and β+
23
12𝑀𝑔
→
23
11𝑁𝑎
+ +10𝑒
Electron Capture

An electron from the
closest energy level
falls into the
nucleus, which
causes a proton to
become a neutron.
 The atomic # goes
down by one and
the mass number
remains unchanged.
0
𝑒−1
+ 𝑝11 → 𝑛10
81
36𝐾𝑟
+
0
−1𝑒
→
81
35𝐵𝑟
Isotopic notation symbols
Remember
𝐴
𝑍
𝑒𝑙𝑒𝑚𝑒𝑛𝑡
To write equations for decay reactions, we use
isotopic symbols and apply the law of matter
conservation.
Let’s write the symbols for these particles.
Balancing Nuclear Reaction Equations
Remember
𝐴
𝑍
𝑒𝑙𝑒𝑚𝑒𝑛𝑡
The reaction arrow separates reactants from products.
The mass numbers, and the atomic numbers,
must add up equally on both sides.
How long does decay take?

Half life: the time required for ½ of a
radioactive sample to decay.

Nuclear reaction rate changes over time –
first fast, then more slowly.
What doesn’t change, however, is the half
life.
 Examples: Am-242: 16 hours
At-218: 2 seconds

Gd-152: 1 x1014 years
Half life graphs
Amount remaining, or
“counts” is plotted on
the y axis.
When amount goes
to ½, one half-life
has passed.
Carbon dating