How do valence electrons relate to the periodic table

Each column gains an electron, group 1a, the alkali earth metals all have one valence electron, group 2a, alkali metals, have two electrons, the noble gases in 8a have eight valence electrons, which complete valence charge, each element can only hold 8 electrons in its outer shell.

the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.

all eukaryotic cell have mitochondria : )