Answers section

Questions 2.16a

1. Why do you think that the invisible particles in one substance may not be identical to the particles in other substances? --------------------------------
2. The pictures you have observed are of pure substances. Each of them consists of the same kind of simplest invisible particles; so they cannot be divided into simpler substances by chemical means. Therefore they are called chemical elements.
   1. Define a chemical element. -----------------------------------------
   2. Name five examples of elements. --------------------------------------------

In the diagram below, we have used the same colour to represent the same kind of invisible particles.








3. Suppose one simplest particle of carbon combines chemically with one particle of oxygen, the product is This is not a simple substance because it can be chemically split into simpler substances . It is called a compound.
   Define a compound. ---------------------------------------------------------
4. In the example given, a particle of carbon combines chemically with a particle of oxygen. They are the smallest particles that take part in a chemical reaction, and are therefore called atoms. Here, the balls represent atoms.
   What is an atom? ------------------------------------------------------------
5. Some substances exist in small independent units, called molecules. That is, as small groups of chemically combined atoms but which exist independently of one another. The combined atoms can be of the same element or of different elements. See the examples below.
   
   
   
   
   
   Define a molecule. -------------------------------------------------------------------------
6. Identify as free atoms, element, molecule, or compound what each of the following drawings represents. Some of them belong to more than one category.