Ionic Compounds Vs. Molecular Compounds

A compound is a substance which is made up of two or more elements and the physical and chemical properties of these compounds differ from its constituent elements. Compounds are classified into ionic and molecular compounds. The comparative study of ionic compounds vs. molecular compounds requires a proper understanding of the composition and structure of these compounds.

Ionic Compounds

The union of metals and non-metals leads to the formation of ionic compounds. These are solid at room temperature and soluble in polar solvents like alcohol and acetone.

These compounds are a mixture of anions and cations. During the formation of such compounds, the metal ion releases electrons and the non-metal ion accepts these electrons. This results in the formation of positively charged cations and negatively charged anions. The energy produced during the formation of such compounds is called lattice energy.

These are usually hard and brittle, because an electrostatic force keeps the ions together in these compounds. These are crystalline in nature. A lot of energy is required to separate the positive and negative charges in ionic compounds. This is due to their high melting and boiling points.

These are good conductors of electricity in dissolved state. In solid state, ions are not held apart as electrostatic forces hold the ions in a fixed position. In a dissolved state, ions get separated from each other towards their respective electrodes in an electric field and become free to conduct electricity. Reaction of ions take place at a very fast rate in these compounds. These ions get charged in solvent state and move very fast. These reactions are called ionic reactions.

Ammonium ions are made up of only non-metals but it is also an ionic compound. This is one of the exceptions. If you come across any non-metals from the halogen group, like Cl, Br, I or NO₃ attached with a non-metal, then they too are ionic compounds.

The naming convention of these compounds is very simple. First, name the positive ion followed by the negative ion. An anion is named followed by a suffix -ide. For example, in the compound KI the ions present are K+ and I-. K+ is a cation and it is denoted as potassium and I- is an anion and it is denoted by iodide and hence the name is potassium iodide.

Some examples of ionic compounds are sodium chloride (NaCl), hydrogen sulfide (H₂S), calcium carbonate (CaCO₃), magnesium fluoride (MgF₂), etc.

Molecular Compounds

Two or more non-metallic atoms unite together to form molecular compounds and that is why they are easily identifiable. In these compounds, sharing of electrons take place between the molecules by covalent bonding. The sharing of a pair of electrons between atoms is called covalent bonding.
These exist in three forms in standard temperature and pressure (STP) - solid, liquid and gas. These are bad conductors of electricity. These compounds are not as hard in comparison with ionic compounds.

In these compounds, the attraction between the molecules is called inter-molecular attraction. The intermolecular force of attraction is a weak force and therefore less energy is required to separate these molecules from each other. Therefore, they have low melting and boiling points.

The molecular compounds which have their own positive and negative charge are called polar molecules. Some of them have no charge separation due to irregular shape and are called non-polar molecules. Polar molecules are soluble in water and insoluble in non-polar solvents like organic solvents.

In accordance with the naming convention, the elements present in a molecular compound are defined based on increasing group number followed by a prefix which denotes the number of atoms present in that group. Unless the first atom is a mono, a prefix is added in all other cases. For example, the systematic name of water is di hydrogen mono oxide (H₂0). Examples of these compounds are ammonia (HN₃), water (H₂O), carbon-dioxide (CO₂) and so on.

This was some information on the differences between ionic compounds vs molecular compounds. It is important to know the diversity of these compounds as we are dealing with them everyday. Chemistry is present everywhere, and believe it or not, the formation of water is also a chemical reaction! Isn't that interesting?