Example 3. Hemoglobin is responsible for carrying oxygen from the lung to all tissues of the body
. Here oxygen refers to oxygen gas, a simple substance.Example 4. Passing electricity through water, H2O, which consists of hydrogen and oxygen, results in the decomposition of water to hydrogen and oxygen, which bubble off
. This is an interesting one. In the first part of the sentence, the terms "hydrogen and oxygen" are used to describe the elements, i.e., the two types of atoms that a molecule of water is composed of. However, for "hydrogen and oxygen" at the end of the sentence, simple substances are meant, the oxygen and hydrogen gases that effervesce (bubble off) on passing an electric current through water.
Still confused? Try to think of different breeds of dogs. A dog breed is a type
of dog having a distinctive appearance and other characteristics, such as temper, weight, hair color, running speed, etc. For instance, when you hear someone say "German Shepherds are great dogs to keep", you picture immediately that particular type
of athletic and agile dog, their approximate size, shape of the head, body, and tail, as well as many other characteristic features of the breed. It is the combination of the features that determines the breed and that you can easily visualize in your mind's eye. However, you cannot pet, feed, or walk a breed because a breed is a type
of dog, not a particular dog. Now imagine that your neighbor calls you saying "I have to be away from home tonight. Could you walk my German Shepherd after dinner?" In this case "German Shepherd" means a particular dog, your neighbor's dog that you can walk and play with. Chemical elements and dog breeds are not tangible because they are just types
of atoms and dogs. In contrast, simple substances and real existing dogs are material
physical bodies (physical objects).
There is one more important difference between an element and a simple substance formed by atoms of this element. An element that is critically needed by a biological system for its proper functioning may, at the same time, form a simple substance that is highly toxic to the same system. For example, we would not exist without considerable amounts of phosphorus as a chemical element that is present in many complex substances that our body contains and needs. Yet as a simple substance, phosphorus (white phosphorus, P4
) is a lethal poison. 1.3.3. Exercises.
Determine if a chemical element or a simple substance formed by this element is meant in the following phrases.
1. Chlorine is a toxic gas. Answer
2. Spinach is rich in iron. Answer
3. Bromine is a liquid at room temperature and atmospheric pressure. Answer
4. Of all metals, tungsten (W) has the highest melting point. Answer
5. Your body needs phosphorus. Answer