From forensic poisonings to radioactive decay, this TED-Ed companion resource uncovers the periodic table’s deadliest secrets. Students will explore how toxic, reactive, and radioactive elements like thallium, mercury, lead, and polonium impact human health and society. This high-interest chemistry and public health lesson includes 20 deep discussion questions, a writing prompt that connects chemistry to ethics and policy, and a debate topic exploring whether dangerous elements should be strictl