Write the electronic configuration of the following elements a. Cesium (Use Noble Gas Short Cut) b. Calcium b._______________. c. Aluminum c._______________
The Correct Answer and Explanation is:
a. Cesium (Cs)
Atomic number: 55
Electronic configuration: [Xe] 6s¹
b. Calcium (Ca)
Atomic number: 20
Electronic configuration: [Ar] 4s²
c. Aluminum (Al)
Atomic number: 13
Electronic configuration: [Ne] 3s² 3p¹
Explanation (Textbook Style – ~300 Words)
In chemistry, the electronic configuration of an element describes the distribution of electrons in atomic orbitals. This arrangement is essential in understanding an element’s chemical behavior, reactivity, and place in the periodic table. The noble gas shortcut, also called the noble gas notation, is a simplified way to write electronic configurations. It uses the symbol of the nearest previous noble gas in brackets, followed by the remaining electron configuration. This method avoids writing the full configuration, which can become lengthy for elements with many electrons.
Cesium (Cs) has an atomic number of 55, meaning it has 55 electrons. The nearest noble gas before cesium is xenon (Xe), which has 54 electrons. Therefore, cesium’s configuration is written as [Xe] 6s¹, indicating that after xenon’s configuration, the 55th electron goes into the 6s orbital. This single 6s electron is why cesium behaves like other alkali metals—it is highly reactive and tends to lose one electron to form Cs⁺.
Calcium (Ca) has 20 electrons. The noble gas before calcium is argon (Ar), which has 18 electrons. The remaining two electrons go into the 4s orbital, giving calcium the configuration [Ar] 4s². This configuration explains why calcium is in Group 2 (alkaline earth metals); it tends to lose two electrons to form Ca²⁺ ions.
Aluminum (Al) has 13 electrons. Neon (Ne) is the noble gas with 10 electrons, so the remaining three electrons go into the 3s and 3p orbitals: two in 3s and one in 3p, yielding [Ne] 3s² 3p¹. This configuration shows aluminum has three valence electrons, which it typically loses to form Al³⁺ ions. This explains its metallic and conductive properties.
Understanding electronic configurations is key to predicting chemical bonding and periodic trends.
