Elements, atoms, molecules and substances

You may, for example, see it written that aluminium is one of the most abundant elements in the Earth s crust . This, of course, does not mean that macroscopic particles of the light, silvery metallic substance from which jumbo jets and saucepans are largely fabricated are to be found in nature. Element has become a collective term, and encompasses all the atoms having a particular atomic number, regardless of their state of chemical combination. We must therefore be careful to refer to an elemental substance if that is what we mean. Thus when we say that lead occurs in sulphide minerals , we are referring to an element the statement that lead reacts only slowly with dilute hydrochloric acid obviously 

As noted in Section 1.3, the terms molecule and substance tend to be used interchangeably by organic chemists, who are usually dealing with substances which consist of discrete molecules. There is a tendency among students to do likewise in inorganic chemistry. This harks back to the late nineteenth century, when inorganic chemists were accustomed to 

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