Question

topic5 d4 assessment periodic table
6 of 42

1. why are both hydrogen and cesium s - block elements, when hydrogen has one electron and cesium has 55?

they have identical electron configurations.
the s - block includes only the most reactive elements.
blocks of elements on the periodic table are based only on an elements valence electrons.
all blocks contain at least one element from each period.

Explanation:

The periodic table is divided into blocks (s, p, d, f) based on the sub - shell in which the valence electrons are present. For s - block elements, the valence electrons are in the s - sub shell. Hydrogen has a valence electron configuration of \(1s^{1}\) and cesium has a valence electron configuration of \(6s^{1}\). The number of total electrons in an atom is not what determines the block. The s - block is not defined by reactivity (for example, hydrogen is not as reactive as some alkali metals in the same block in the same sense). Also, it is not a rule that all blocks contain at least one element from each period.

Answer:

Blocks of elements on the periodic table are based only on an element's valence electrons.