Notes on Types of Substances

As discussed before matter is made of atoms and molecules. Some are made of the same atoms or molecules while others are made of different molecules. When the matter is made up of the same atoms or group of atoms it is considered a substance. We define pure substance or simply substance as something which cant be separated by any kind of physical separation method. That’s how we answered the question of what is pure substance.  It can be further classified into 2 other types elements or compounds

Compounds vs Elements

A thing common in both compounds and the elements is that these substances are made up of multiple connected atoms. A substance meaning pure is that it is made up of only one kind of molecule. Molecules are made by connecting the different atoms through bonds.  You will get to know about the concepts like valence and bonding in your higher classes.

An element is a substance that is made up of molecules that contain a given atom only. For example, O2 is an element as this substance is only made up of the oxygen atom. While a compound is a substance made of molecules that are made of multiple connected atoms of different types. For example, CH4 is a compound. It is made of different types of atoms joined by bonds. 

There are several types of elements that don’t exist as molecules but are found as monatomic species. The name of many expensive and important elements falls in this class of the matter referred to as substance. Gold, Platinum, Nickel and gases like He do exist as monatomic species. 

Substance: Your Opinion vs Chemists Opinion

Let us see what explanations we can draw when we are talking about substance meaning Pure substance is different from an impure one.  We call a matter impure if we can separate the different particles in it by some physical changes. To be more precise when we say a matter to be impure we mean that it is not made of the type of particles as per their chemistry. These particles may be either atoms, molecules or ions. We are going to refer to impure matter as mixtures of pure substances. We classify mixtures as follows:

1) Homogeneous mixture:- When we say a substance is a homogeneous mixture we are referring to an impure substance in which the impurities are evenly distributed. In simple words, it looks the same throughout if you look at any section of a homogeneous mixture. For example; a salt solution is a homogeneous mixture.

2) Heterogeneous mixture:-   When we are referring to a substance to be a heterogeneous mixture we mean that it is a substance in which the impurities are not evenly distributed. The different sections of a heterogeneous mixture are clearly different in all aspects. For example; a mixture of oil and water is clearly a heterogeneous mixture. 

When in general people around us are saying a substance to be pure, they are not concerned about the chemical nature of its constituent particles. The question of what is a pure substance is answered by laymen and by chemists in a completely different manner.  Generally, in society, a pure substance means something which is not harmful to us. And there are also some standards set by us. Like we will say a substance to be impure if that impurity i.e. the other substance present in the mixture is not desired as per our standards. That is how we differ in opinion about what is a pure substance.

Colloidal Solution

To make things a little simple consider a binary solution. A solute of a very small size constitutes a true homogenous solution. A solute of bigger size (generally visible) makes a heterogenous mixture called suspension. If the particle size is in between the size for a true solution and that for a suspension, then it is a colloidal solution. Milk is a most famous example of a colloidal solution. Colloidal solutions have the particles of the size range 1 nanometer to 1 micrometre. 

A colloidal solution is a heterogeneous mixture. The solute particles in a colloidal solution are not uniformly distributed. Though this non-uniform nature is not clearly visible by our eyes. This property makes it different from other heterogeneous mixtures. Now for a bigger mixture i.e. for other than binary solution, we can say that the different particles are not uniformly distributed though they are not visible. 

Conclusion

In the above paragraphs we have discussed the types of substances. And also the type of mixtures. We have also seen the types of mixtures that are hard to be called impure e.g. milk.  We can see how the different classes of substances like colloidal solution were classified and differentiated from pure substances. The societal standards to see purity is somehow really different from the scientific perception of seeing what is a pure substance. The pure substance should comprise the particles of the same kind only. If you are going to talk about the everyday experience we may not be able to differentiate between a homogenous mixture and a pure substance. But here we have also seen how a heterogeneous mixture known as the colloidal solution is also not easily distinguishable from pure substances. To have a better understanding readers are advised to read about the adsorption dispersed phase and the dispersion medium.