Sodium, represented by the symbol \(\text{Na}\), is a common alkali metal found in substances like table salt (\(\text{NaCl}\)). It plays an important part in nerve signaling and fluid balance within the human body. Understanding sodium’s chemical and biological functions requires examining the fundamental particles that make up its atomic structure.
Atomic Structure of Sodium
The most abundant and stable form of sodium found in nature is Sodium-23 (\(\text{Na}^{23}\)). The nucleus of a neutral sodium atom contains two types of particles: protons and neutrons. A neutral sodium atom always contains 11 protons.
The stable Sodium-23 isotope has 12 neutrons in its nucleus. Protons and neutrons are collectively known as nucleons and account for nearly all the atom’s mass.
Decoding the Periodic Table: Atomic and Mass Numbers
The number of protons within an atom’s nucleus is the defining characteristic, known as the atomic number (\(Z\)). For sodium, the atomic number is 11; any atom with 11 protons is, by definition, a sodium atom. Altering the number of protons transforms the atom into a different element entirely.
The mass number (\(A\)) provides the total count of protons and neutrons combined within the nucleus. The stable sodium isotope, Sodium-23, has a mass number of 23. The number of neutrons is calculated by subtracting the atomic number from the mass number (\(A – Z\)). Thus, \(23 – 11\) confirms that stable sodium has 12 neutrons.
Sodium’s Electron Count and Ionic Charge
In a neutral sodium atom, 11 negatively charged electrons orbit the nucleus, balancing the 11 positively charged protons. These electrons are arranged in shells in the configuration 2, 8, 1, meaning there is only one electron in the outermost, or valence, shell.
Atoms seek maximum stability, typically achieved by having a full outer electron shell. Sodium easily loses its single valence electron rather than gaining seven more to fill the shell. When the atom loses this electron, it forms the positively charged sodium cation (\(\text{Na}^{+}\)). The resulting \(\text{Na}^{+}\) ion retains 11 protons but has only 10 electrons, giving it a net charge of \(+1\) and the stable electron structure of neon.
When Neutron Counts Change: Understanding Sodium Isotopes
While the number of protons is fixed at 11, the number of neutrons can vary, creating different forms of the element known as isotopes. Sodium-23, which has 12 neutrons, accounts for virtually all naturally occurring sodium. Other isotopes exist but are unstable and radioactive.
For example, Sodium-24 (\(\text{Na}^{24}\)) has 13 neutrons, and Sodium-22 (\(\text{Na}^{22}\)) has 11 neutrons. These radioactive isotopes are used as tracers in medical and research applications. Sodium-24, with a half-life of about 15 hours, is specifically used to track sodium’s path in the human body to monitor electrolyte uptake.