Both sunlight and air appear to fill up the classroom space. Hardly do we offer any classroom demonstration that air has measurable mass, but the sunlight does not. We possibly need not emphasize the distinction between mass and weight on the first day of class. Our simple unequivocal definition of chemicals is any stuff that can be stored for future use, in contrast to energy that must be consumed right away and can be stored only as energy-rich chemicals like food and fuel. Every change in chemicals involves energy.
Energy is, therefore, an essential and integral part of all chemical studies.
Energy, inter convertible with chemicals, can even be taken as a property of the later. Matter is only a trivial name for chemicals. The health effects depend on the nature, and route of entry of a chemical, and on the genetic make up, body weight, and sex of the individual exposed, but primarily on the dose. All chemicals are harmless or beneficial in small amounts. Defined by LD50, a spoonful of botulinium toxin can be lethal to the entire population of the United States.