Nuclear Reactions

Beta decay occurs when the nucleus emits a beta particle. Beta particles have a negative charge and are much smaller than alpha particles. They’re equivalent to high-speed electrons and are symbolized by or . This type of radioactivity causes an increase in the atomic number by 1 but no change in mass number. The equation below represents uranium-233 undergoing beta decay.

How does a nucleus, which is composed of only protons and neutrons, eject an electron? A neutron is composed of a proton and an electron fused together. In beta emission, the electron is emitted from the nucleus, while the proton part remains behind, thus increasing the atomic number by 1.

Example

Complete the balanced equation by determining the missing term.

Explanation

Remember, the sum of the atomic numbers and the mass numbers must be equal on both sides of the equation. We are looking for a component that has mass number of 80 and an atomic number of 34 (34 protons). Using this information and the periodic table, we can identity the element produced by this beta decay as Se, or selenium. The missing term is Se.And the completed equation is:

Gamma decay consists of the emission of pure electromagnetic energy; no particles are emitted during this process, and it is symbolized by equation;00g. After beta, positron, or alpha decay, the nucleus is left in a high-energy state, and at this point it will often emit gamma rays, which allows it to relax to its lower-energy ground state. Since gamma rays do not affect charge or mass, they are often not included in nuclear equations.

Positron emission occurs when an atom becomes more stable by emitting a positron 01e, which is the same size and mass as an electron but has a positive charge. This process converts a proton into a neutron; the positron is emitted and the neutron remains behind in the nucleus, decreasing the atomic number by 1.

Often the emission of an alpha or a beta particle creates another radioactive species, which undergoes further radiation/emission in a cascade called a radioactive series. Notice that in the course of all of these types of radioactive decay, neither protons nor neutrons are either created or destroyed: this is due to what’s known as the law of conservation of matter, which states that mass is neither created nor destroyed. So when you see radioactivity equations on the SAT II Chemistry test, one of the most important things to remember is that the sum of the mass numbers and the sum of the atomic numbers must both be equal on both sides of the equation.

Example

Write the equation for the alpha decay of radium-221.Write the equation for the beta decay of sulfur-35.

Explanation

The radium-221 atom has atomic number (A) = 88 and mass number (Z) = 221. When an alpha particle is emitted, the atomic number is reduced by 2 and the mass number is reduced by 4. The atomic number of the resulting atom is 86, so the element created as a result of this radioactive decay is radon-217.

The sulfur-35 atom has an atomic number of 16 and a mass number of 35. When it undergoes beta decay, the atomic number is increased by 1 and the mass number remains the same. The atomic number of the atom created is 17, so the atom is chlorine-35.

There are two main types of nuclear reactions: fusion and fission. In fusion reactions, two light nuclei are combined to form a heavier, more stable nucleus. In fission reactions, a heavy nucleus is split into two nuclei with smaller mass numbers. Both processes involve the exchange of huge amounts of energy: about a million times more energy than that associated with ordinary chemical reactions. In either case, if the new particles contain more stable nuclei, vast quantities of energy are released.

Nuclear power plants rely on fission to create vast quantities of energy. For example, U-235 nuclides can be bombarded with neutrons, and the result is lots of energy, three neutrons, and two stable nuclei (Kr-92 and Ba-141). The three neutrons formed can collide with other U-235 atoms, setting off a chain reaction and releasing tons of energy.

Example

Is the following process an example of fission or fusion?

Explanation

This is an example of fission. Fission occurs when a large nucleus is bombarded by a small particle, such as a neutron. The result is two smaller nuclei and additional neutrons, and a chain reaction process begins.