From left to right across a period in the periodic table, elements become less and more in their properties. 26. francium has 36 isotopes, but only francium-223 occurs in nature. francium-223 spontaneously emits particles and energy, so francium-223 is a(an) of francium. 27. at sea level, water at 100°c. 28. cooking requires continuous addition of energy to the chemical reactions that are taking place. the chemical reactions involved in cooking can be described as