Question

Atomic number of strontium (Sr) is equal to:
A.28
B.38
C.42
D.34

Answer 1

Alkali earth metals are the elements with fully filled s-orbital in their neutral state. They usually form mild bases with hydroxide ions and are thus known as alkali earth metals.

The alkali earth metals are six elements present in group 2 of the periodic table. The elements have very similar properties, they are all shiny, silvery-white and somewhat reactive at standard temperature and pressure. They have a general electronic configuration of ${\text{n}}{{\text{s}}^2}$ . They lose electrons and form cations with the oxidation state of $ + 2$ . All these elements are found on earth naturally. The heavier elements in this group tend to be more reactive than the lighter ones. This is because, as we go down the group, the force of attraction between the nucleus and the outermost shell decreases and thus they form cations more easily. They mostly form ionic compounds except beryllium which forms covalent compounds due to its high charge density and small size.
Strontium is present in the fifth period of the periodic table. It has an electronic configuration of $\left[ {{\text{Kr}}} \right]5{{\text{s}}^2}$ . As we know that the atomic number of krypton is 36. So, the atomic number of strontium will be $36 + 2 = 38$ . So, the atomic number of strontium is 38.

$\therefore $ The correct option is option B, i.e. 38.

The alkali earth metals also have important biological roles. Magnesium and calcium are essential to all living organisms. Magnesium acts as an active site in many cellular processes and calcium is present in our structures as bones. Strontium plays an important role in marine aquatic life, as corals use strontium to build their outer shells. Beryllium and radium are toxic. Beryllium is toxic due to its small size causing its unique characteristics and radium due to its radioactivity.