Introduction to Strontium
Strontium (symbol Sr) is a chemical element with atomic number 38. It is an alkaline earth metal, characterized by its silvery-white appearance and high reactivity. Like other elements in its group, Strontium is never found freely in nature but occurs combined with other elements in minerals. Its chemical properties are similar to those of Calcium and Barium. A notable use of Strontium compounds is in fireworks, where they impart a brilliant red colour, often seen during festivals like Diwali across India.
Basic Properties
The atomic number of Strontium is 38. This number represents the count of protons within the nucleus of a Strontium atom. For a neutral atom, the number of electrons is equal to the number of protons. The most common isotope of Strontium has a mass number of 88.
Atomic Structure of Strontium
Understanding the atomic structure involves identifying the subatomic particles—protons, neutrons, and electrons—and their arrangement within the atom.
Protons, Neutrons, and Electrons
- Protons: The atomic number of Strontium is 38. Therefore, a Strontium atom contains 38 protons in its nucleus. Protons carry a positive charge.
- Electrons: In a neutral Strontium atom, the number of electrons is equal to the number of protons. Thus, a neutral Strontium atom contains 38 electrons, distributed in energy shells around the nucleus. Electrons carry a negative charge.
- Neutrons: The mass number (A) of the most common isotope of Strontium is 88. The number of neutrons is calculated by subtracting the atomic number (Z) from the mass number (A). Number of neutrons = Mass Number - Atomic Number Number of neutrons = 88 - 38 = 50 neutrons. Neutrons are electrically neutral particles found in the nucleus alongside protons.
Electron Configuration
Electron configuration describes the arrangement of electrons in the atomic orbitals and shells. For Strontium, with 38 electrons, the electron configuration can be written in two ways:
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Full Electron Configuration: This lists all the occupied orbitals in order of increasing energy. $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2$ This configuration indicates:
- 2 electrons in the 1s orbital.
- 2 electrons in the 2s orbital and 6 electrons in the 2p orbitals.
- 2 electrons in the 3s orbital, 6 electrons in the 3p orbitals, and 10 electrons in the 3d orbitals.
- 2 electrons in the 4s orbital and 6 electrons in the 4p orbitals.
- 2 electrons in the 5s orbital.
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Noble Gas (Condensed) Electron Configuration: This uses the symbol of the preceding noble gas to represent the core electrons, making the configuration more concise. The noble gas preceding Strontium is Krypton (Kr), which has 36 electrons. $[Kr] 5s^2$ This shows that the electron configuration of Strontium consists of the stable electron configuration of Krypton, followed by 2 electrons in the 5s orbital.
Valence Electrons
Valence electrons are the electrons located in the outermost shell of an atom. These electrons are primarily involved in chemical bonding. For Strontium, the outermost electron shell is the 5th shell. From the electron configuration $[Kr] 5s^2$, it is observed that there are 2 electrons in the 5s orbital. Therefore, Strontium has 2 valence electrons. The presence of these two valence electrons places Strontium in Group 2 (alkaline earth metals) of the periodic table, and they are readily lost to form a positive ion with a charge of +2.
Common Uses of Strontium
Beyond its application in pyrotechnics for producing red colours in fireworks, Strontium compounds have various industrial uses. Strontium-90, a radioactive isotope, is a by-product of nuclear fission and finds use in radioisotope thermoelectric generators (RTGs). In some medical applications, strontium is used in medications for osteoporosis, and it has historical use in cathode ray tube (CRT) displays for televisions and computer monitors.