How can one show that elements that have different appearances have similar chemical properties?

Elements within the same group have the same number of electrons in their valence (outermost) shells, and they have similar electron configurations. They exhibit similar chemical properties.

it's filtration, but this is an assumption so my apologies if i got this

answer:

the answer is 6 valence electrons.

explanation:

valence is the # of electrons on the outer most shell of an atom.

oxygen has 6.

although, the valency of oxygen is 2, because it only needs to make 2 covalent bonds, or gain 2 electrons, to achieve the stable octet configuration of a noble gas.

that's it!

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~ trueboss72