The question of how many electrons a sodium ion possesses requires understanding the difference between a neutral atom and an ion. Sodium (Na) is an alkali metal found in table salt and is necessary for human health. To determine the electron count, we must first look at the structure of the neutral sodium atom and then examine the process by which it gains its positive charge.
The Neutral Sodium Atom
A neutral sodium atom is defined by its atomic number, which is 11, meaning its nucleus contains 11 protons. In its neutral, uncharged state, an atom must have an equal number of electrons orbiting the nucleus to balance the positive charge of the protons, thus a sodium atom has 11 electrons.
These 11 electrons are arranged in distinct energy levels, or shells, surrounding the nucleus. The first shell is full with 2 electrons. The second shell holds its maximum of 8 electrons, completing the electron configuration for the inner shells.
This leaves the final, 11th electron alone in the third and outermost shell. This single electron is called the valence electron, and its presence largely determines the chemical behavior of the sodium atom. The electron configuration of a neutral sodium atom can be summarized as 2-8-1 across its three occupied shells.
Forming the Sodium Ion
The sodium ion is formed when the neutral sodium atom undergoes a chemical change called ionization. During this process, the atom loses its single, loosely held valence electron from the outermost shell. This loss results in a particle with a net electrical charge, which is the definition of an ion.
By losing one electron, the sodium atom changes its electron count from 11 to 10. The resulting particle is specifically called a cation because it carries a positive charge.
The symbol for the sodium ion is written as \(Na^+\). This indicates that it has one more proton (11 positive charges) than it has electrons (10 negative charges). The 10 electrons that remain are tightly held in the first two complete shells, giving the sodium ion a new, stable electron arrangement of 2-8.
The Drive for Stability
The reason sodium readily loses its single valence electron is explained by the Octet Rule. This rule states that atoms tend to react in ways that allow them to achieve a full outer shell containing eight electrons, a highly stable configuration.
For a sodium atom, gaining seven electrons to fill its outermost shell is chemically very difficult. It is much easier for the atom to shed the one electron in the third shell. When this sole electron is removed, the third shell effectively disappears, and the second shell, which already contains a stable set of eight electrons, becomes the new outermost layer.
The sodium ion, with its 10 electrons, now possesses the same stable electron configuration as the noble gas Neon. This change from the neutral atom’s unstable 11-electron configuration to the ion’s stable 10-electron configuration is the primary motivation for the formation of the sodium ion in chemical reactions.