An ion is an atom or molecule with an electrical charge, which results from an imbalance between positively charged protons and negatively charged electrons. When an atom loses electrons, it develops a net positive charge and is called a cation. Conversely, an atom that gains electrons acquires a net negative charge and is known as an anion. Strontium, a metallic element, consistently forms a positively charged ion, meaning Strontium is a cation.
Strontium’s Chemical Identity
Strontium is classified as an Alkaline Earth Metal, a group of elements located in Group 2 of the periodic table. A neutral Strontium atom has an atomic number of 38, indicating it contains 38 protons and 38 electrons. Its placement in Group 2 dictates a distinct and predictable chemical behavior.
Every element in the Alkaline Earth Metal family, including Strontium, shares the characteristic of possessing two electrons in its outermost energy shell. These outermost electrons are known as valence electrons, and they determine how an atom will interact with other elements. Strontium is a soft, silvery-white metal that is highly reactive, a property directly linked to these two valence electrons.
The Formation of the Strontium Ion
The formation of the Strontium ion is driven by the Octet Rule, a fundamental principle of chemical stability. This rule suggests that atoms react to achieve a full outer shell of eight valence electrons, mimicking the stable noble gases. Since the neutral Strontium atom has only two valence electrons, it must achieve this stable configuration.
Strontium has two paths to stability: gaining six electrons or losing the two electrons it possesses to expose the full shell beneath. Gaining six electrons requires massive energy, making it energetically unfavorable. The much easier path is to lose the two outer valence electrons.
When the Strontium atom loses its two electrons, the balance between its 38 positive protons and negative electrons is disrupted. It retains 38 protons but now has only 36 orbiting electrons. This two-electron deficit results in a net positive charge of +2. The stable ion formed is the Strontium cation, represented by the chemical symbol \(\text{Sr}^{2+}\).
Strontium Ions in Context
The \(\text{Sr}^{2+}\) cation is the common and stable form of Strontium found in nature and commerce, appearing in various ionic compounds. This ion is particularly noteworthy in biological systems because of its close chemical relationship with the calcium cation, \(\text{Ca}^{2+}\). The two ions have a similar ionic size, allowing the body to sometimes mistake Strontium for Calcium.
Because of this similarity, Strontium ions are readily incorporated into human bone tissue, where they can mimic the function of calcium. This property has been utilized in certain medical treatments, such as Strontium Ranelate, which manages osteoporosis by stimulating new bone formation and reducing bone breakdown.
The Strontium cation is also a component in common commercial products. For example, Strontium Chloride is often included in toothpaste formulations to help alleviate tooth sensitivity. Another notable application is in pyrotechnics, where the presence of the \(\text{Sr}^{2+}\) ion is responsible for producing the characteristic brilliant crimson-red color in fireworks and safety flares.