Strontium (Sr) is an alkaline earth metal, placing it in the second column of the periodic table. It is a soft, highly reactive element that naturally exists as a solid. A neutral Strontium atom holds precisely 38 electrons. This fixed number determines the element’s chemical identity and behavior.
Determining the Electron Count
The number of electrons in a neutral Strontium atom is linked to its atomic number (Z), which is 38. The atomic number indicates the exact number of protons found within the nucleus.
Protons carry a positive charge, which must be balanced by an equal number of negatively charged electrons in a neutral atom. This principle of electrical neutrality requires the number of electrons to match the number of protons.
Since Strontium’s atomic number is 38, it contains 38 protons. Consequently, a neutral Strontium atom must possess 38 electrons to maintain an overall zero charge.
Arrangement of Strontium’s Electrons
The arrangement of the 38 electrons determines Strontium’s chemistry. These electrons are organized into distinct energy levels, or electron shells, surrounding the nucleus. The electrons fill these shells sequentially, starting with the lowest energy levels closest to the nucleus.
The distribution across Strontium’s five energy levels is summarized by the shell configuration 2, 8, 18, 8, 2. The innermost four shells hold 2, 8, 18, and 8 electrons, respectively. The final two electrons occupy the outermost, or fifth, energy level.
Orbital Notation
A more detailed description uses orbital notation, which specifies the sublevels within each shell. The full electron configuration shows how the 38 electrons fill the various s, p, and d orbitals: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 5s2.
Valence Electrons
The shorthand notation simplifies this by using the nearest preceding noble gas, Krypton (Kr), which accounts for 36 electrons: [Kr] 5s2. This notation highlights the two outermost electrons in the 5s orbital, known as the valence electrons. These valence electrons are the most loosely held and participate in chemical bonding.
Strontium Ions and Electron Loss
Strontium rarely exists as a neutral atom because it is highly reactive, like all alkaline earth metals. It is almost always found as an ion in chemical compounds. Strontium achieves stability by following the Octet Rule, which means attaining a full outer shell similar to a noble gas.
Strontium achieves this stability by readily losing its two valence electrons from the 5s orbital. The loss of two negative charges leaves the atom with an excess of two positive charges from the protons. This results in the formation of the Strontium ion, represented as Sr2+.
The resulting Sr2+ ion retains 38 protons but possesses only 36 electrons. This electron count gives the ion the same stable electron configuration as the noble gas Krypton, [Kr]. Therefore, the chemically stable Strontium ion has a final electron count of 36.