Calcium has an atomic number of 20 and 2 valence electrons. Oxygen has an atomic number of 8 and 6 valence electrons. Neon has an atomic number of 10 and 8 valence electrons. Explain how the placement of these three elements on the periodic table compares and why they are placed where they are relative to each other.

Why is it important for scientists to review and repeat the work of other scientists? 1.a scientific theory must be tested three times before it is proven. 2.the scientific method only applies to repeated experiments. 3.an experiment may have had errors that the scientists didn't recognize. 4.the results of individual scientists may be influenced by bias. 5.an experiment must be performed twice before the data can be analyzed.