A mixture is composed of a variety of atoms. These atoms are usually not bound together in a chemical way. Mixtures are categorized into two broad categories; homogenous and heterogeneous. In a homogenous mixture, all the portions that make the mixture are somewhat similar and once the mixture has formed, it would be almost impossible to tell the presence of two elements. The example of sugar and water is a kind of a homogenous mixture. A heterogeneous mixture on the other hand is one in which the atoms that comprise the mixture are dissimilar. Homogenous mixtures are often referred to as solutions. This implies that one can actually tell the presence of two or more elements just by observation of with a naked eye. An example would be a mixture of sand and sugar (Aldridge, 2009).

On the other hand, a compound consists of a variety of elements which have been bound together by some chemical process. This implies that in a mixture, it is possible to physically locate the different atoms and inmost of the cases one can actually separate the two by a purely physical procedure. In compounds however, it may not be possible to see the different elements and separation of the constituent elements can only be achieved through some chemical process.  In fact, the separation of compounds would sometimes lead to the destruction of one of the elements.

The constant composition law is the best approach to understanding the difference between the two. According to the law, mixtures don’t have a constant composition unlike the compounds which have a constant composition. For instance, water will always be composed of 11.2 percent hydrogen and an oxygen percentage of 88.8. That means that water is a compound. But if you had two elements together like water and milk, the composition would vary depending on the person mixing them. This would be a good example of a mixture.

How to tell the difference

If you had a pure substance and you needed to tell whether it was a compound or a mixture, you will need to establish whether the substance comprised of separable elements. Even though pure substances are almost similar to homogenous mixtures, the difference is that a pure substance will show uniformity of composition all through while a mixture might have a discrepancy here and there. The important rule to apply is that pure substances can not be further broken down into other substances unless their properties are changed first and this can only happen in a chemical process (Aldridge, 2009).

Subjecting the substance to some physical separation tests will suffice to establish whether or not it is a pure substance. This would include such tests as dissolving in water, evaporation, filtering, freezing or melting depending on the state of the substance. If none of the physical procedures can separate elements that have formed the substance, then it will be confirmed to be a pure substance.

Ionic and covalent bonds

Atoms usually react in a chemical process to join to form compounds. The force that holds them together is usually referred to as bonds. These bonds can either be ionic or covalent bonds. When the ions with dissimilar charges attract to form the bond between the different atoms, the n the bonds are referred to as ionic. Consequently, if the ions that are similar are the ones that are responsible for the bond formation, the bonds will be described as covalent bonds. Usually, the inorganic are said to be of ionic bonds. Sodium chloride is one such example. It is formed by reacting sodium (Na) and Chlorine (Cl) to get sodium chloride (NaCl). Unlike is the case for the covalent bonds, sodium does not share electrons. On the contrary, it gives up its extra ion to chlorine resulting in the formation of the ionic bond. Covalent bonds usually form organic compounds. In such a scenario, the different elements combine by sharing the ions. An example of such a bond is one found in methane demoted as CH4. The different electrons in the Hydrogen molecule share the carbon molecule to form a covalent bond (Aldridge, 2009).

Ionic compounds

These compounds form as a result of a metal from the left side reacting with a non metal from the right of the periodic table. They are also referred to as the metals. They are usually described as being electropositive. This means that they easily lose their delocalized electrons. Metals will therefore react by loosing electrons which makes them to be positively charged. This makes them form ionic compounds. Some examples are magnesium oxide and lithium hydride. Ionic bonds can be formed in two different ways. When the electrons are shared equally, the resulting bond can be described as non-polar. If however, the electrons have not been shared equally, then the bond that forms will be formed as a polar bond. Sodium chloride is an example of an ionic bond. Sodium reacts by releasing its delocalized electron to chlorine thereby forming an ionic bond (Aldridge, 2009).

Covalent compound

Covalent bonds are formed when nonmetals from the right side of the periodic table bond with each other. The elements that are found on the right side of the periodic table are described as being electronegative. It means that they easily accept electrons. They are also referred to as the non-metals.  When these elements react by accepting electrons, they become negatively charged ions. The term anion is therefore used to refer to them. An example of a covalent bond can be seen in the methane (CH4) compound. The different electrons in the Hydrogen molecule share the carbon molecule to form a covalent bond (Sadish, 2010).

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