In 1911, Rutherford concluded that an atom is a positively charged dense center with a negative electron cloud. A nucleus contains a neutron and a proton. Symbolic wise, A is the mass number, Z is the atomic number, and X is the atom.
Radioactive decay is seen commonly under these two conditions:
1) 84 or more protons
2) neutron: proton ratios not equal to 1
History:
Chemical reactions occur as a result of the interaction between valence electrons. In 1896, Henri Becquerel discovered that uranium emitted radiation and concluded that nuclear changes occur. Shortly after, Marie Curie began studying radioactivity. Curie proposed that radiation was a property of atoms as opposed to compounds.
Radioactivity is the natural change of an isotope of an element into an isotope of a different element. Nuclear reactions involve changes in the nucleus and thus a change in the atom itself. Generally, elements heavier than Bi have natural radioactivity and thus decays. The protons of an atom define the element and thus a change in and atom is caused by a change in protons. This leads us to the following types of decay.
Overview:
Nuclear Decay:
There are 5 different types of radioactive decay.
1.Alpha decay:
A is the initial isotope and B is the isotope formed. In alpha decay an element looses two neutrons and two protons.
Alpha decay cannot penetrate deeply compared to the other types of decay.
Elements with atomic numbers greater than 83 commonly decay through Alpha.
EX:
Alpha decay cannot penetrate deeply compared to the other types of decay.
Elements with atomic numbers greater than 83 commonly decay through Alpha.
EX:
2.Beta decay:
The beta increases by 1 proton. Ideally, although not shown, the atom loses a neutron to balance out the atomic mass. Beta negative decay is more penetrating than alpha decay because it is smaller, but less penetrating than gamma decay.
Beta decay is common in elements with a high neutron: proton ratio.
EX:
Did you know?
Beta electrons can shoot through 1 cm of flesh before electrostatic forces stop it.
Beta decay is common in elements with a high neutron: proton ratio.
EX:
Did you know?
Beta electrons can shoot through 1 cm of flesh before electrostatic forces stop it.
3.Gamma decay:
In gamma decay, nothing is changed. The gamma ray is given off when the electrons fall into a lower energy state. Gamma is the most penetrating of all decays.
EX:
Did you know?
The gamma ray photons can pass through the body easily. These rays would then damage the body by ionizing the molecules in its way.
EX:
Did you know?
The gamma ray photons can pass through the body easily. These rays would then damage the body by ionizing the molecules in its way.
4.Positron or Beta positive decay:
When a proton forms into a neutron ending with a neutral charge, positron decay has occurred. Lighter elements with a low neutron: proton ratio decay commonly through positron.
EX:
EX:
5.Electron capture:
In this, the initial element atom captures an electron and thus, its atomic number is decreased. The electron joins with a proton and forms a neutron.
Did you know?
Sadly, mercury cannot decay into gold at a fast enough rate through electron capture. This makes it undesirable and impractical.
Zone of Stability
We have been talking about stability and why an atom decays. As stated, the least stable atoms are those with a 1:1 neutron to proton ratio. The middle darker dots are those are generally stable. However, as more neutrons and protons are considered on an atom, the ratio needs to increase a bit to reach stability.
Decay Series
This chart shows the series of decay of U to form a stable Pb atom. U goes through a series of beta and alpha decays. When there is no slope on a line on the graph above, beta decay is represented because Z increases by 1 but A doesn’t change. The diagonal arrows represent alpha decay because we cam see that Z changes by 2 and A by 4.
The series of decay in
since alpha decay accounts for the only change in A. In the decay above, A changes by 32 and since alpha changes that value by 4, we can tell that there is definitely 8 alpha decays in this series.
In
, 8 alphas show a 16 electron change in the decay.
Since,
96-16 electrons in alpha decay, there is another 6 electrons short of forming 82Pb. Therefore, 6 beta decays are required in order to add 6 electrons to form
