Patients who waited more than 6 months to receive cataract surgery experienced more vision loss, a reduced quality of life and had an increased rate of falls compared with patients who had wait times of less than 6 weeks.
The chalcogens, the oxygen group, is located in column 16 of the periodic table. It contains the elements oxygen, sulfur, selenium, tellurium, polonium, and ununhexium (O, S, Se, Te, Po, and Uuh, respectively). These elements all contain six valence electrons and form 2- ions.
The oxygen atom has therefore 8 neutrons, 8 protons and 8 electrons. The number of valence electrons is equal with the group number. Since oxygen is in group 6 it means that it has 6 valence electrons. Check out the periodic table from the web site above. You will see that the number of protons and electrons are easy to determine.