The element with Z = 20 is

The element with atomic number (Z) 20 is Calcium (Ca) [t3][t4]. According to its electronic configuration, Calcium has 20 electrons arranged as 2, 8, 8, 2 in the K, L, M, and N shells respectively [c1]. This configuration shows that it has two electrons in its outermost (valence) shell [c1][t6]. In the periodic table, elements are organized into groups based on their chemical properties and valence electrons; Calcium belongs to Group 2 [t3][t5]. Elements in Group 2 are specifically classified as alkaline earth metals [t1][t3]. These metals are characterized by their reactivity, tendency to form +2 ions, and the basic (alkaline) nature of their oxides [t2][t6]. Therefore, Calcium is an alkaline earth metal, distinguishing it from alkali metals (Group 1), halogens (Group 17), and inert gases (Group 18) [t1][t3].

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 3: Metals and Non-metals > 3.3 HOW DO METALS AND NON-METALS REA ALS REACT? > p. 47
2. [2] https://www.energy.gov/sites/prod/files/2020/07/f76/The%20Periodic%20Table%20of%20Elements.pdf
3. [3] https://periodic.lanl.gov/20.shtml