Write a nuclear equation for positron emission by each nuclide. (a) Co-55 (b) Na-22 (c) F-18

A nuclear equation is much like a chemical equation but instead shows the changes that occur within an atom's nucleus during nuclear reactions. Positron emission is one such nuclear reaction, where a proton inside the nucleus is transformed into a neutron and a positron. The positron is then ejected from the atom.

For example, with Cobalt-55 undergoing positron emission, we see that it decays into Iron-55 with the emission of a positron. To express this in a nuclear equation, we first write the parent nucleus (Cobalt-55), followed by the arrow indicating the reaction. After the arrow, we show the resulting daughter nucleus (Iron-55) and the emitted positron. In nuclear notation, this decay is represented as: \[^{55}_{27}Co \rightarrow ^{55}_{26}Fe + ^0_{+1}e\].

Understanding and writing nuclear equations requires recognition of the changes in atomic and mass numbers. In the case of positron emission, the atomic number decreases by one (since a proton is lost), and the mass number remains the same because a neutron is gained in place of the proton, and the positron itself has negligible mass.

In discussing radioactive decay, it's imperative to grasp that it is a natural process by which an unstable atomic nucleus loses energy by emitting radiation. In the form of positron emission—anatural type of beta decay—a proton is converted into a neutron with the simultaneous release of a positron, which is ejected from the nucleus.

A positron is a particle with the mass of an electron but a positive charge. It's helpful to envision radioactive decay like a tree losing its leaves: just as a leaf's detachment is part of the tree's lifecycle, so too is radioactive decay a fundamental process for certain unstable elements striving for a more stable state. In our textbook example, nuclides like Co-55, Na-22, and F-18 undergo positron emission in their decay process.

• Co-55 decays into Fe-55 with a positron release.
• Na-22 decays into Ne-22 with a positron release.
• F-18 decays into O-18 with a positron release.

In each case, this decay process helps the nuclide achieve greater stability.

Nuclear notation is a shorthand way of expressing the composition of atomic nuclei. It provides clear information about an element's atomic number, mass number, and, in the case of ions or isotopes, electrical charge or neutron count.

To thoroughly understand nuclear notation, let's dissect the notation for sodium-22 (\[^{22}_{11}Na\]). The lower left subscript (11) represents the atomic number, which coincides with the number of protons and, in a neutral atom, also the number of electrons. The upper left superscript (22) designates the mass number, which is the combined total of protons and neutrons in the nucleus.

When a nuclide undergoes positron emission, we must also account for the positron in our notation. A positron has a notation of \[^0_{+1}e\], denoting its negligible mass and +1 charge. For students, visualizing the nuclear notation can be aided by thinking of it as an atomic 'address' that gives all the information you need to identify the 'residence' of a nucleus within the periodic table—a clear and systematic way to represent an atom's fundamental characteristics.