Why is it called the periodic table of elements (why is the word periodic in it)

It is called "periodic" because elements are lined up in cycles or periods. From left to right elements are lined up in rows based on their atomic number (the number of protons in their nucleus). ... Each horizontal row in the table is a period. There are seven (or eight) total periods.

Explanation:

i would say b

explanation:

but i think i would need more information than that

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