S block elements of the periodic table one made up of

Analyze the question: The question asks which groups of the periodic table make up the s-block elements.

Explain the concept: Elements are placed into blocks (s, p, d, f) according to the sub-shell that receives the last (valence) electron.

• The s sub-shell can hold a maximum of 2 electrons.
• So the s-block has only two groups: elements whose outermost electron configuration is ns¹ or ns².

Show the solution:

1. Group 1 (alkali metals): Li, Na, K, etc. The configuration ends in ns¹, so they belong to the s-block.
2. Group 2 (alkaline earth metals): Be, Mg, Ca, etc. The configuration ends in ns², so they also belong to the s-block.
3. Group 3 and beyond: In the older Nigerian syllabus, Group 3 (B, Al) is where the p sub-shell begins to fill (ns² np¹). Groups 3 to 7 (and 0) are therefore the p-block, not the s-block.

Checking the options:

• A. Groups 1, 2, 3: wrong, because Group 3 is p-block.
• B. Groups 1 and 2: correct.
• C. Group 3: wrong.
• D. Groups 3 to 7: wrong, because this is the p-block.

Answer: The s-block elements are those in Groups 1 and 2, which is option B.

Tip: Remember "s = 2 electrons = 2 groups". The s-block is Groups 1 and 2 (helium is also placed in the s-block by configuration, 1s², though it sits with Group 0 or 18). The p-block has 6 groups because the p sub-shell holds 6 electrons.