How are elements labeled on the periodic table that have the same number of
valence electrons?

Explanation:

Elements that have most similar properties were placed in the same group on the periodic table and this is done based on the number of valence electron each of the element posses which allow them reach in a similar manner as a member of the same family. A group of element is placed on a a vertical column of the periodic table.

For all element with one valence electron they are labelled with 1A on the group, and are usually the first column followed by 2A until group 8.

1A element are known to be very reactive and form compounds with similar properties with other elements.

"record the time to complete a chemical reaction" would most likely be part of a lab procedure.