Compound and mixture have fairly simple dictionary meanings in the English language but when studied as terms in chemistry they become more complicated.
Compound vs Mixture
The main difference between Compound and Mixture is that a compound is created by mixing two or more elements together chemically and in a definite proportion. An easy example would be salt which is a compound because it contains two elements – sodium and chlorine. A mixture is created when two or more substances are combined physically in indefinite proportions. Cement is a mixture because it is made up of sand, water, and gravel.
Since the elements are chemically bound in a compound, they cannot be taken apart by physical means. Unlike compounds, the different substances in a mixture can be separated using physical methods.
Comparison Table Between Compound and Mixture
| Parameter of Comparison | Compound | Mixture |
|---|---|---|
| Definition | Two or more elements are chemically bound to form a compound, | Two or more substances are combined physically to form a mixture |
| Types | Homogenous | Homogenous and Heterogeneous |
| Separation | Chemical means | Physical means |
| Proportion | Definite and fixed | Varies |
| Result | New substance is created | No new substance is created |
What is a Compound?
Chemically binding two or more chemical elements
together creates a compound. The atoms that make up these elements are bound
together using their electrons and by binding them together, a new substance
which is a compound is formed.
The proportion in which the elements are bound together is definite and fixed. The formula for each compound is written according to the elements that form it and their proportion.
The formula for water is H2O. This shows that water is a compound made up of two atoms of hydrogen and one atom of oxygen. Atoms bond together in different ways and the bonds that create compounds are categorized accordingly.
In cases where one atom gives an electron and the other gains one, an ionic bond is formed. The electric charge of the atoms changes upon losing and gaining electrons and they become ions.
When we look at the example of sodium and chlorine, an electron from the sodium is transferred to the chlorine. Sodium becomes a cation because it becomes positive and chlorine becomes an anion because it becomes negative.
This is an ionic bond and the formula for the compound this creates is NaCL which in layman terms is salt. Covalent bonds are the most commonly occurring of all bonds. Rather than an electron is transferred from one atom to another, in covalent bonds, electrons are shared between the two atoms.
These two electrons create another orbit that surrounds both atoms thereby binding them together into a molecule. Unlike ionic bonds that are created due to the attraction between the opposing charges, covalent bonds are formed between atoms with similar electronegativity.
An example of a covalent bond is carbon monoxide which is formed by the bonding of one carbon atom with one oxygen atom. Whereas covalent bonds are formed with negatively charged atoms, metallic bonds are formed between positively charged atoms.
This type of bond is formed between metal atoms.
Here the free electrons in both atoms are shared in lattice form without either one losing or gaining electrons. Platinum is an example of a metallic bond.
What is a Mixture?
In a mixture, two substances are combined together in a physical manner. However, the chemical composition of each substance remains the same.
Therefore they can be separated using physical means. Unlike a compound, the proportion of the substances in the mixture can vary and need not be definite.
It is important to note that while the chemical composition does not change, the physical properties of the substance in the mixture will change when they are brought together.
No new substance is formed. Mixtures can be classified into two types – homogenous and heterogeneous. When a mixture has a uniform composition, it is a homogenous mixture.
Separating its components isn’t easy as usually one is a solute and the other is a solvent.
Even in cases where there are multiple components like the air around us which contains a myriad of gases, there are solutes like oxygen and carbon dioxide balanced with a solvent like nitrogen making it a homogenous mixture.
A normal example would be a saline solution which is just a mixture of water and salt. On the other hand, a heterogeneous mixture lacks uniformity. Particles of the substances involved can be differentiated and separating them is easy.
For example, if sand and stones are mixed together, it would not be difficult to separate the stones from the sand. Besides this simple classification, mixtures can also be categorized based on the size of the particles they contain. In this manner, mixtures can be divided into solutions, suspensions, and colloids.
Solutions are homogenous mixtures. The size of the particles is minuscule and once mixed, they cannot be viewed separately. Moreover, the solute will completely dissolve in the solvent. The mixture of salt and water would fall into this category.
When a homogenous mixture has particles that are of medium size, the mixture is a colloid.
Here the particles can be viewed separately even after mixing but they can be separated by filtering. Fog and jelly are examples of a colloidal mixture.
Lastly, we have suspension mixtures that are heterogeneous. The particles in these mixtures are large and not evenly distributed. Suspension mixtures are further divided into three.
In a solid-solid mix, solids are mixed together and they can be easily separated by sifting. A classic example of a solid-solid mix is soil. Next, come solid-fluid mixtures which contain solids mixed with liquids or gases. Even after being mixed together, the ingredients will separate.
If the solids are heavier than the liquid or gas, the solid particles will gradually sink to the bottom. If they are lighter they will rise and float on top of the mixture. Therefore when dust mixes with the air, it is a solid-fluid mixture as dust is heavier than air. These mixtures can usually be separated through filtration.
The final category of suspension mixtures is fluid-fluid mixtures. Here even though liquids or gases are mixed with other liquids or gases, one will be heavier than the other and so it can be viewed separately.
If oil and water are mixed together, globules of oil will remain suspended in the water without dissolving.
Main Differences Between Compound and Mixture
- A compound is formed when two or more elements are chemically bound together.
- Mixtures are formed when two substances are combined physically.
- Compounds have elements that are combined in definite proportions.
- The proportion of the substances in a mixture can vary.
- The elements of a compound are chemically bound and cannot be separated by physical means.
- Since the substances in a mixture do not face any alteration in their chemical composition they can be separated using physical means like filtration and sifting.
Conclusion
In simple terms, two elements come together in a chemical bond to create a whole new substance with its own properties and this is called a compound.
On the other hand, when two substances are combined together but aren’t chemically bound, they form a mixture in which each of the substances retains its earlier physical properties.
References
- https://pubs.acs.org/doi/pdf/10.1021/ac60081a007
- https://pubs.acs.org/doi/abs/10.1021/es401604b