Cesium (Cs) tends to be the most reactive of the alkali metals (francium is radioactive and has not been well studied). Based on your understanding of atomic radius, effective nuclear charge, and ionization energy, explain why this is true. 15. Time to Reflect…Consider everything you’ve learned in lab and lecture about periodic trends. In your own words, explain why it is important to know how the periodic table is organized. How do you think knowledge on periodic trends (ionization energy, electron affinity, atomic radius, electronegativity, etc.) help you, personally, in your future as scientist and/or engineer? 10. Explain how the reactivity with acid relates to the location of the metals on the periodic table.