Periodic Classification of Element — Important Questions

Li, Na, K, Cl, Br, I, Ca, Sr, Ba

Li, Na, K (alkali metals), Cl, Br, I (halogens), and Ca, Sr, Ba (alkaline earth metals) are valid Dobereiner's triads as they have similar chemical properties and follow the atomic mass relationship.

Number of valence electrons

Elements in the same group have the same number of valence electrons in their outermost shell, which gives them similar chemical properties.

s-block, p-block, d-block, f-block

The modern periodic table is divided into four blocks: s-block (groups 1-2), p-block (groups 13-18), d-block (groups 3-12), and f-block (lanthanides and actinides). There is no g-block.

Nuclear charge increases

As we move from left to right in a period, the nuclear charge increases while electrons are added to the same shell. The increased nuclear charge pulls electrons closer, reducing atomic size.