Mendeleev's Periodic Table Insights

A guy in the 1800s predicted elements that hadn't even been discovered yet,

and he was right. That chemist, Mendeleev, realized the periodic table isn't random;

it’s a cheat sheet for how elements behave. It all follows a pattern called periodicity.

For example, as you move across the table, atoms actually get smaller because

their core pulls electrons in tighter. But as you move down, they get bigger

by adding new layers. This is why elements in one column, like the alkali metals,

react explosively with water, while elements in another, like the noble gases,

are super unreactive.