Difference Between Compound and Mixture

Introduction

In our daily lives, we encounter various chemicals such as salt, water, baking powder, toothpaste, vinegar, etc. All these chemical substances are of paramount importance to living beings. From a chemistry point of view, we can classify these chemicals as compounds and mixtures. The fundamental knowledge of compounds and mixtures is very important to understand the basic properties of matter and its components. It also helps us to understand the various chemical reactions occurring constantly in nature. Let us explore the important differences between compounds and mixtures, which could help us unveil the intricate properties of nature and matter.

Compound vs Mixture

A compound is a combination of two or more elements formed chemically in a fixed ratio, whereas a mixture is a combination of elements. A chemical reaction occurs for the formation of a compound, which leads to the formation of chemical bonds. No chemical reaction occurs in the formation of the mixture, and hence, no chemical bonds are formed.

Difference Between Compound And Mixture In Tabular Form

Parameters of Difference	Compound	Mixture
Definition	A compound is a chemical substance formed chemically by the combination of two or more elements.	Its Boiling and melting points are constant
Reaction	The reaction occurs in the formation of a compound	No reaction occurs
Separation	Cannot be separated easily as chemical bonds are present	Can be separated by physical means
Composition	Elements are combined in a fixed ratio by mass	Elements are not combined in any fixed ratio
Temperature	Its boiling and melting points are not constant	Its boiling and melting point are not constant
Properties	The properties of a compound is different from that of the constituent elements	The properties of a mixture are the same as that of the constituent elements

What is a Compound?

In today’s time, 118 elements are known to exist according to the modern periodic table. All the matter we see today is the result of these elements or the combination of these elements. Elements constitute only one kind of atom, which cannot be broken further by any means. For example, a carbon molecule consists of only carbon atoms. Similarly, the molecules of oxygen, silver, and iron consist of their respective atoms.  When these elements combine with the help of chemical bonds in a certain proportion, they are called compounds. For example, Sodium chloride (NaCl) is a compound that is formed by sodium cation (Na⁺ ) and a chloride anion (Cl ^- ). Carbon dioxide (CO₂ ) is formed by one atom of carbon and two atoms of oxygen. Millions of chemical compounds exist in nature. Chemical changes are mainly responsible for the formation of compounds. A chemical change is one in which different substances combine to form a new substance. This phenomenon could be referred to as a chemical reaction as well.

 We can categorize these compounds under two fundamental types.

Ionic Compound

Ionic compounds are substances wherein, a cation and an anion attract each other to form a chemical compound. A cation is formed when a metal loses its electron and becomes positively charged, while an anion is formed when a non-metal gains an electron and becomes negatively charged. The resulting bond formed between the two ions is known as an ionic bond. An ionic bond is chiefly formed when there is a large electronegativity difference between the two ions. The fundamental entity formed as a result of an ionic bond is known as a lattice structure.

Sodium chloride is formed by a sodium cation( Na⁺ )and a chloride anion ( Cl ^- ). Potassium fluoride ( KF), silver iodide (AgI), and calcium sulfate ( CaSO₄) are some other examples of ionic compounds.

Let us take a look at the various characteristics of ionic compounds

• Ionic compounds are comprised of both metals and non-metals.
• They form crystalline structures due to strong electrostatic forces of attraction.
• They can be hard and brittle.
• They have high boiling and melting points due to powerful electrostatic forces of attraction between the ions.
• They don't conduct electricity in a solid state due to the absence of mobile ions, but they can conduct electricity in a molten or dissolved state as the ions become free to move in the water. Therefore, in solid state, ionic compounds act as good insulators.
•  These substances dissolve in water but lack dissolvability in non-polar solvents. The solubility of these substances increases with an increase in their covalent character.
• Ionic compounds possess elevated enthalpies of fusion and vaporization.

Covalent Compound

A covalent compound is one, wherein, sharing of a pair of electrons occurs between two atoms. The bond formed here is known as a covalent bond. Basically, covalent bonds are formed between the atoms having high ionization energy ( energy required to extract an electron from the outermost shell of an isolated gaseous atom ) that are unable to transfer electrons and atoms having low electron affinity ( energy released when an electron enters the outermost shell of an isolated gaseous atom), as they cannot accept electrons. The atoms of such elements combine with the atoms of others or the atoms of the same elements to complete their octet and achieve stability. Thus, a covalent bond is formed. Hydrogen, oxygen, carbon dioxide, water, methane, etc., are some examples of covalent compounds.

Now, Covalent Bonds can be divided into three types based on the number of bonds present in the molecule.

Single Covalent Bond

A single covalent bond refers to the bond formed when a single pair of electrons is shared between two atoms.

Example: HCl is an example of a single covalent bond. In an HCl molecule, one electron from Hydrogen and one electron from chlorine come together to form a single bond.

Double Covalent Bond

A double covalent bond refers to the bond formed when two pairs of electrons are shared between two atoms.

Example: O₂ is an example of a double covalent bond. Two electrons from each oxygen atom are shared to form two bonds.

Triple Covalent Bond

A triple covalent bond refers to the bond formed when three pairs of electrons are shared between two atoms.

Example: N₂ is an example of a triple covalent bond. Three electrons from each nitrogen atom are shared to form three bonds.

Based on polarity, covalent bonds can be divided into two types.

Polar Covalent Bond

Before we explore the concept of polar covalent bond, it's essential to understand what electronegativity means. The ability of an atom of a particular element to attract a shared pair of electrons toward itself is referred to as electronegativity. If two atoms are bonded together, and the electronegativity of one atom is greater than the other, the shared electron will shift slightly towards the atom with higher electronegativity. Polar covalent bonds typically form between atoms with uneven electron distribution, resulting in an unbalanced electron density between them. This uneven distribution of electrons is caused due to the difference in electronegativity between the two atoms. Polar covalent bonds exclusively form between two distinct atoms. HCl, H2O, CO, HBr, NH3, etc., are some examples of polar covalent bonds.

Non-Polar Covalent Bond

Non-Polar Covalent bonds are often formed between the atoms having equal distribution of electrons, resulting in a balanced electron density between them. For the electrons to be distributed equally,  the electronegativity of both atoms should be the same. Non-polar covalent bonds can arise between atoms of the same element or maybe different elements. H_2, Cl₂, Br₂, CH_4, CO₂, etc., are examples of non-polar covalent bonds.

Let us take a look at the characteristics of covalent compounds:

• The covalent compound typically comprises non-metals.
• They exist in gaseous, liquid, or solid state.
• Covalent solids are mainly soft and malleable.
• Covalent compounds' boiling and melting points are low as they have low intramolecular forces of attraction.
• Covalent compounds don’t conduct electricity in solid, liquid, or molten states as covalent bonds are formed by the sharing of electrons. Since all the electrons are involved in this sharing process, there are no free electrons available, resulting in the absence of electrical covalent compounds that lack solubility in water, however, they readily dissolve in organic compounds.
• Their enthalpy of fusion and vaporization are low as they have low intramolecular forces of attraction.

In addition to the two fundamental types, chemical compounds exhibit various other types.  They can be as follows:

Organic Compounds

Compounds containing carbon atoms connected to one another and other elements, such as Hydrogen, Oxygen, Nitrogen, etc., are known as organic compounds.

Acid Compound

Compounds that give a mixture when dissolved in water are called acid compounds.

What is a Mixture?

Scientifically, a mixture is a substance resulting from the combination of two or more distinct substances. Unlike compounds, mixtures do not form any chemical bond. Instead, a mixture is formed by physically amalgamation of two or more substances. To be more specific, mixtures are a result of physical change. Physical changes are the processes that lead to the transformation of the physical properties of a substance without any change in its chemical composition. They can be separated by physical means. The components of a mixture retain their original properties. Air is a mixture of various gases such as oxygen, nitrogen, carbon, etc. Sea water is a mixture of salt and water. Smoke is a mixture of smoke and fog. Milk is a mixture of various vitamins and minerals. Petroleum is a mixture of various hydrocarbons.

Types of Mixtures

Homogeneous Mixtures

Homogeneous mixtures are mixtures that have a uniform distribution of the components throughout, resulting in a consistent composition. A mixture of salt and water is a homogenous mixture as the salt molecules are uniformly distributed among the molecules of water.

Properties of Homogenous Mixtures

• The distribution of the components is uniform throughout. 
• They exist in a single phase.
• They cannot be separated by any physical means.
• They don't exhibit the Tyndall effect.
• Solutions are commonly Homogeneous mixtures.

Heterogeneous Mixture

Heterogeneous mixtures are mixtures that have an unequal distribution of components throughout.  A mixture of sugar and salt is heterogeneous as the salt molecules are not distributed uniformly among the sugar molecules.

Properties of Heterogeneous Mixtures

• The distribution of components isn’t uniform.
• They can exist in two or more than two phases.
• They can be separated by physical methods.
• They exhibit the Tyndall effect.

Colloids

Colloids are a heterogeneous mixture in which the molecules of one particle are dispersed in the other particle. The size of the molecules can range from 1-1000 nm. Generally, in a colloid,  the solute particles form the dispersed phase, and the solvent particle forms the dispersion medium. Unlike suspensions, the particles do not settle at the bottom of the container. They remain dispersed throughout the solution. Therefore,  we can say that colloids are substances that exist between a true solution and suspension. Colloids can be of various those such as:

• Sol: blood,  paint, mud
• Emulsion: gel, cheese, butter
• Foam: whipped cream, soap
• Aerosol: fog, mist, fume

Suspension

A suspension is a kind of heterogeneous mixture in which the individual particles remain suspended. The particles do not dissolve and are thus visible through the naked eye. If left undisturbed,  the particles would settle at the bottom due to the effect of gravity. 

Examples of suspension are sand in water, milk of magnesium, chalk in water, dust particles in air, etc. 

Main Differences Between Compound and Mixture in Points

• Compounds are formed by the combination of two or more elements that are united chemically, whereas a mixture is formed by the combination of two or more elements that are united physically.
• During the formation of chemical compounds, chemical bonds are formed as they involve chemical reactions but during the formation of a mixture,  no chemical bonds are formed as they are made physically.
• As the compounds contain chemical bonds, the components cannot be separated easily, but in the case of mixtures, the components can be readily separated by physical means.
• A compound is formed chemically by mixing fixed proportions of elements to produce a substance with unique characteristics and properties. Mixtures are formed by mixing components physically without taking any fixed proportions. Hence, the properties of the mixture obtained can be altered by changing the number of components used.
• Compounds are chemical entities. Therefore, they have fixed melting and boiling points. Mixtures do not have fixed melting and boiling points, as the quantity of components can be altered by changing a mixture's physical and chemical properties.
• The properties of the compound formed are always different from the components used as during the formation of a compound, rearranging of atoms occurs and hence,  it results in a completely new substance. In the case of mixtures, the properties of the substance formed remain the same as the properties of the components used, as there is no rearranging of atoms in mixtures.
• Compounds are considered as homogeneous. Mixtures can be either homogeneous or heterogeneous.
• The formation of compounds involves a change in energy, but no energy change is involved in the distinct mixtures.

Conclusion

Now, we can summarize that compound and mixture are distinct entities with their individual characteristics and properties. We can also conclude that the knowledge of compounds and mixtures is extremely important to understanding the fundamental concepts of chemistry. Compounds are formed by combining two or more elements chemically whereas mixtures are formed by combining two or more elements physically. The distinction between compounds and mixtures is important to understand the nature of various matters that exist and their uses in the scientific and non-scientific worlds.

References

• https://www.britannica.com/science/chemical-compound
• https://www.geeksforgeeks.org/what-is-a-mixture/
• https://www.thoughtco.com/mixture-definition-chemistry-glossary-606374