Ionic and molecular compounds can be distinguished by comparing their physical characteristics. At room temperature, ionic compounds are often solids, have high melting and boiling temperatures, and perform poorly as electrical conductors. On the other hand, molecular compounds often have lower melting and boiling temperatures, are generally poor conductors of electricity in both the solid and liquid stages, and are gases or low-melting solids at ambient temperature. In this article, we will explore in detail the difference between Ionic and Molecular compounds. We must first discuss what Ionic compounds and Molecular compounds are.
Ionic Compounds
A compound formed through ionic bonding is known as an ionic compound. One atom transfers its electrons to another in a process known as electron transfer to form an ionic bond. An atom of one element loses one or more electrons during an electron transfer, whereas another atom gains those electrons. In an electron transfer, both atoms involved become ions. When an atom receives electrons, it changes into a negatively charged anion, and when it loses electrons, it changes into a positively charged cation. The ions bond together or are held together by electrostatic forces due to the opposite charges on them. In an ionic bond, oppositely charged atoms are drawn to one another and their charges balance to form neutral compounds. Ionic compounds are formed when a metal reacts with a nonmetal, causing an electron transfer from the metal to the nonmetal. As a result, the nonmetal produces a negative ion or anion, and the metal produces a positive ion or cation.
1. Structure of Ionic Compounds
Ionic compounds often exhibit a crystal lattice structure in the solid state, with the ions arranged in a regular, repeating pattern. Strong electrostatic forces hold the ions together, and the complex as a whole is neutral because the positive and negative charges balance one another. A number of variables, such as the size of the ions, their charge, and the coordination number, can be used to describe the lattice structure of an ionic compound (which refers to the number of ions that are directly bonded to a given ion).
2 Properties
The strong forces that hold the ions together in the lattice structure give ionic compounds their characteristically high melting and boiling temperatures.
Due to the ions' ability to move easily and carry an electrical charge, they also tend to exhibit strong electrical conductivity when melted or dissolved in water.
Ionic compounds, however, are often poor electrical conductors in the solid form because the ions cannot move about freely.
Polar solvents like water can dissolve ionic compounds. Hydrocarbons and chloroform, which are non-polar solvents, cannot dissolve ionic compounds.
They are hard and brittle.
They are electrically neutral.
3. Naming Ionic Compounds
There are particular rules that need to be followed while naming ionic compounds:
Ionic compounds are always written as follows: cation + anion.
The positive charge must be expressed using roman numbers if the cation has more than one charge.
All oxidation numbers must be stated, with the exception of groups 1, 2, and Al3+, Zn2+, Ag+, and Cd2+. If we have Fe3+, for example, we would write it as Iron (III), whereas if we had Zn2+, we would write it as Zinc.
The beginning of the anion's name will remain the same, but the suffix -ide must be inserted.
4. Sample Calculations
Name the compound Na2O Sodium = cation, Oxygen = anion Therefore, the name of the compound will be sodium (cation) + oxygen (anion) The oxygen (anion) will keep the beginning of its name, with the suffix -ide. The name of the compound will be Sodium Oxide.
5. Ionic compound Examples
Chemical formula | Chemical Name | Common Use |
Ca3P2 | Calcium Phosphide | used as a rodenticide and in fireworks |
KI | Potassium Iodide | used as an additive of table salt used to prevent goiter |
Li3N | Lithium Nitride | used as a reducing agent |
MgO | Magnesium Oxide | used as an antacid and laxative |
NaF | Sodium Fluoride | used as an ingredient used in toothpaste |
1. Molecular Compounds
Molecules are groups of atoms that are bonded together and have a unique, independent existence. Molecular compounds are the building blocks of molecules. Covalent bonds, chemical bonds in which atoms share one or more pairs of electrons, hold together molecular compounds that are commonly produced between nonmetals. A molecule is formed when the atoms in a molecular compound are bonded together by covalent bonds in a specific arrangement. The characteristics of the molecule are different from those of the constituent atoms.
1. Structure of Molecular Compounds
The structures of molecular compounds can be linear, bent, trigonal planar, tetrahedral, and octahedral, among others.
The boiling point, solubility, and reactivity of a molecule can all be affected by its form, as can other physical and chemical characteristics.
Also Refer
http://intro.chem.okstate.edu/1314F00/Lecture/Chapter10/VSEPR.html
2. Properties
Intermolecular forces, or the forces between various molecules of the same substance, are responsible for many of the characteristics of molecular compounds.
Molecular compounds have weak intermolecular forces.
At room temperature, molecular compounds are usually gases or liquids. At room temperature, some molecular compounds are solids, but they are usually flexible and soft.
The forces holding molecules together are typically weaker than those holding ions together in an ionic compound, resulting in molecules having lower melting and boiling temperatures than ionic compounds.
Electrons in the covalent bonds are not free to move. They are generally bad conductors of electricity. But some molecular compounds have a high degree of reactivity and can combine with other compounds to produce new ones.
Molecular compounds tend to have low solubility. They are often nonpolar, which makes them difficult to dissolve.
Molecular compounds have no ions and are electrically neutral. They are poor conductors of electricity as they have no charge and no free electrons. Instead, molecular compounds act as effective insulators.
3. Molecular Compounds Examples
Examples of molecular compounds include the following:
A well-known molecular molecule called water (H2O) is made up of two hydrogen atoms bound to one oxygen atom. At room temperature, water is a liquid and is necessary for all known forms of life.
One carbon atom is joined to four hydrogen atoms to form the basic chemical molecule methane (CH4). At room temperature, it is a gas and is frequently used as fuel.
One carbon atom is bound to two oxygen atoms to form the chemical molecule known as carbon dioxide (CO2). At room temperature, it is a gas and plays a significant role in the carbon cycle on Earth.
Three oxygen atoms are joined together to form the chemical molecule ozone (O3). The atmosphere of the Earth contains trace amounts of this extremely reactive gas.
Two chlorine atoms are joined together to form the chemical compound chlorine (Cl2). It is a highly reactive gas that is employed as a bleach and disinfectant.
One nitrogen atom is joined to three hydrogen atoms to form the chemical molecule ammonia (NH3). It is used as a cleaning agent and fertilizer and is a gas at room temperature.
2. Difference between Ionic compounds and Molecular compounds
Basis | Ionic Compounds | Molecular Compounds |
Meaning | Ionic compounds are made up of ions, atoms or molecules with a net positive or negative charge due to the gain or loss of electrons. | Molecular compounds are made up of molecules, which are groups of atoms that are bonded together and have a distinct, independent existence. |
Formation | Ionic compounds are typically formed when a metal reacts with a nonmetal, transferring electrons from the metal to the nonmetal. | Molecular compounds are typically formed between nonmetals. |
Forces | The ions are then held together in a lattice structure by the electrostatic attraction between the positive and negative charges. | Molecular compounds are held together by covalent bonds, chemical bonds in which atoms share one or more pairs of electrons. |
Melting and Boiling points | Ionic compounds tend to have high melting and boiling points because of the strong forces that hold the ions together in the lattice structure. | Molecular compounds tend to have lower melting and boiling points because the forces holding the molecules together are generally weaker than those holding ions together in an ionic compound. |
Conductors | When melted or dissolved in water, they tend to be good conductors of electricity because the ions can move freely and carry an electrical charge. However, in the solid state, ionic compounds are generally poor conductors of electricity because the ions cannot move freely. | They are also generally poor conductors of electricity because the electrons in the covalent bonds are not free to move. However, some molecular compounds can be highly reactive and can undergo chemical reactions with other compounds to form new compounds. |
Enthalpy of fusion and vaporization | Ionic compounds have higher enthalpies of fusion and vaporization. | Molecular compounds have lower enthalpies of fusion and vaporization. |
Key Takeaways
Key Points
Atoms that are electrostatically attracted to one another form ionic bonds, which are the building blocks of ionic compounds.
Covalent bonds, which share electrons between constituent atoms, are the building blocks of molecular compounds.
Ionic compounds create clusters known as crystals because they are surrounded by atoms with opposite charges rather than constituting a single molecular entity.
Ionic bonds are stronger than covalent bonds.
Key Terms
Enthalpy of Fusion: The enthalpy of fusion is the amount of energy required to melt one mole of a solid substance at constant pressure.
Enthalpy of Vaporization: The amount of energy needed to vaporise one mole of a liquid at constant pressure is known as the enthalpy of vaporization.
FAQs
1. How can you tell the difference between ionic and molecular compounds through structure?
Ionic compounds typically have a crystalline structure and are solid at room temperature (with some exceptions). They also tend to have high melting and boiling points. Molecular compounds are usually gases, liquids, or low-melting solids at room temperature. They have relatively low melting and boiling points.
2. What constitutes the basis for ionic and molecular compounds?
Ionic compounds are typically formed between a metal and a nonmetal, while molecular compounds are typically formed between nonmetals.
3. On what factor are the properties of ionic and molecular compounds depend?
The properties of ionic compounds are generally more dependent on the identity of the ions present than the properties of molecular compounds, which are more dependent on the structure of the molecules.
4. Can ionic and molecular compounds exist in the same substance?
Yes, it is possible for a substance to contain both ionic and molecular compounds. For example, many biological molecules, such as proteins and nucleic acids, contain both ionic and covalent bonds. Similarly, some solid materials, such as glass, can have both ionic and covalent bonds in their structure.
5. Can a compound be both ionic and molecular?
Yes, a compound can be both ionic and molecular. These substances include polyatomic ions. Example: NaNO3 - sodium nitrate (NH4)S - ammonium sulfide
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