DUE VERY VERY VERY SOON
What are the rows of elements called on the periodic table?

"The elements are arranged in seven horizontal rows, called periods or series, and 18 vertical columns, called groups."

Explanation:

the number of valence electrons for each molecule or ion is shown beneath the structure. remember hydrogen will not have more than two electrons. this hydrogen is part of a covalent bond (sharing two electrons). a double bond here would cause hydrogen to share four electrons with phosphorus.

answers: to make sure that all of the broken pieces of tablet were added to the water, to allow for fair comparison of all three trials, with different particle sizes to avoid experimental error