Ionic vs molecular compounds
Chemical elements can join with each other to form chemical compounds. The elements are bonded together by chemical bonds which has ionic or covalent characteristics. If the compounds have ionic bonds, they are known as ionic compounds and if they have covalent bonds they are named as molecular compounds. There is a defined ratio of atoms in a compound and they are represented by the chemical formula.
Ionic compounds are formed by the attraction between positive and negative ions. Positively charged ions are known as cations and negatively charged ions are known as anions. Since cations and anions have opposite charges they are attracted to each other with electrostatic forces, forming ionic bonds. Cations are usually formed by metal atoms and the anions are formed by nonmetal atoms. Ionic compounds exist as crystals. Sodium chloride is a common example for an ionic compound. Sodium is a group 1 metal, thus forms a +1 charged cation. Chlorine is a nonmetal, and has the ability to form a -1 charged anion. NaCl has a lattice structure. In the crystal, each sodium ion is surrounded by six chloride ions, and each chloride ion is surrounded by six sodium ions. Due to all the attractions between ions, the crystal structure is more stable. The number of ions present in the crystal varies with the size of it.
Molecular compounds are formed by uncharged atoms. There can be two atoms (N2), three atoms (H2O), or many atoms as in glucose (C6H12O6). These atoms are linked by chemical bonds. Molecular compounds are formed by nonmetals. There are molecules formed by joining the same kind of atoms with a covalent bond such as O2, H2 and S8 etc. There are very small molecular compounds as well as macromolecules such as Protein or DNA. Molecules can also be in a form similar to crystals. For example, graphite and diamond are two molecular crystals of carbon. The exact number of atoms in a molecule is given by the molecular formula. There can be inter molecular attraction forces between molecules, but normally these forces are weak.
Difference between Ionic compounds and Molecular compounds
- Ionic compounds exist as crystals, but molecular compounds can exist as either gas, liquid or solid state.
- In ionic compounds, metals and nonmetals are present. The electrons of the metal element are donated to the nonmetal element, forming an ionic bond. In molecular compounds two or more nonmetals share electrons, and form a covalent bond.
- Ionic compounds are polar. Molecular compounds can be either polar or nonpolar, but they are not polar as ionic compounds.
- Ionic compounds are solvated in polar solvents and release ions; therefore, they can conduct electricity. Molten liquids of ionic compounds can also conduct electricity. In contrast, molecular compounds cannot conduct electricity (except the lattice forming molecular compounds like graphite).
- Molecular compounds may be soluble in organic solvents, but ionic compounds do not.
- Ionic compounds have higher melting points and boiling points compared to molecular compounds. This is due to the higher number of strong electrostatic attractions which are present in a crystal.