How Do Ionic and Covalent Bonds Differ?
Bonding in covalent and ionic compounds is classified according to the character of electrons, which are delocalized. This classification is based on electronic effects, for which bonding is a result of interaction among electrons of different orbitals and hence is a chemical bonding. As a result of this interaction, electrons become shared by two or more nuclei, leading to a reduction in the electron energy and therefore stabilization of the compound. A compound whose nucleus accepts an electron is termed an electron acceptor and a nucleus that donates a single electron is an electron donor.
The delocalized electron is called the valence electron, which can be donated by a nucleus. Electrons in orbitals can be assigned energies concerning the nucleus of the atom. For example, an electron in the 1s orbital, which is localized around a nucleus, has high energy, and when the atom gains energy, the electron is donated to the nucleus to make the atom more stable. For an atom to be stable, it must gain the maximum amount of energy, and hence it is called a 'maximum donor'. Electrons with high energy are called 'high valence' or 'heavier' electrons.
The bond between atoms can be classified as either covalent or ionic following the number of electrons transferred. The number of transferred electrons to bond with a molecule to make it more stable is termed the valence. In a chemical bonding reaction, a bond with one electron transferred is termed a single bond, two electrons transferred is a double bond, three electrons transferred is a triple bond, and the maximum bond strength is denoted by a covalent bond. In general, the higher the valence of an atom, the stronger the bond between them is.
The chemical bonding of atoms can be classified as one of the following: ionic, covalent, metallic and van der Waals. Among these, ionic is a bond formed when two or more elements share electrons in their outer shells. However, all ionic bonds are not created equally. There are covalent, metallic and van der Waals bonds in ionic bonding.
Covalent Bonding
In a covalent bond, the nucleus of an atom accepts electrons of the other atom. The electron configuration is as follows:
There is one outer shell electron for both the donor and the acceptor atom.
One orbital is the highest in energy, which accounts for the greater bonding in covalent bonding.
The bond energy is the highest among all of the types of chemical bonding, owing to the greatest attractive force.
In a covalent bond, the bond energy is approximately 2-3 kcal mol−1 more than in an ionic bond. To illustrate the above-stated principle, in an electron exchange reaction in which one electron is transferred from donor atom A to the acceptor atom B, the nuclei of the atoms become ionic and the electron configuration of the atoms change from 2 _n_ − 2 to _n_ + 2. A covalent bond is considered when the electron configuration becomes 2 _n_ + 1 (in a diatomic molecule, the two atoms are of the same type).
Metallic Bonding
In a metallic bond, the electrons of the nucleus of both the atoms are shared between them, unlike the covalent and ionic bonds. The electrons form new chemical species which do not exist individually. The electrons cannot be assigned individually to the nucleus, and the two molecules share each electron in common.
Metallic bonds are extremely strong and they form through s-p mixing in d-orbitals.
In a metallic bond, the bond energy is lower than covalent bonding. However, owing to strong forces and a low percentage of electrons, the bond energy is weak and the bonds are easily broken.
Van der Waals Bonding
Van der Waals (vdW) bonding is similar to ionic bonding. One of the atoms in the molecule is ionic and the other is electrically neutral. In van der Waals bonding, the electrically neutral atom attracts the ionic atom. The interaction between the neutral atom and the ionic atom is of an opposite sign than that of the covalent bonds. This leads to attractive force and attraction between them. The strength of van der Waals bonding is not so strong.
Ionic Bonding
An ionic bond is very strong, owing to the presence of ions. The positive ions of one of the atoms are shared with the negative ions of the other atom. One of the atoms of the ionic compound has more electrons than the other. This one atom is positively charged. The electrically neutral atom has fewer electrons than the other atom. This atom is negatively charged. The charge on an atom increases or decreases if it loses or gains electrons, respectively.
Ionic bonding also involves an exchange interaction between the positive charge on one atom and the negative charge on the other atom. The covalent bonds of both atoms exist when the positive charge on one atom is neutralized by the negative charge on the other. Ionic bonding is different from ionic bonding in the following ways:
In an ionic bond, all the valence electrons are shared between two different atoms. In a covalent bond, only one valence electron of an atom remains.
In ionic bonding, the interaction between the positive charge on one atom and the negative charge on the other atom is not the same as the interaction between two like charges. In covalent bonding, both the interaction and force between two like charges are similar.
The charge separation of ions from an atom causes attraction. In covalent bonds, both the atom and the bonding electrons have the same charge.
Ions have higher mobility than non-polarized charges.
FAQs on Ionic and Covalent Bonds Explained
1. What is an ionic bond and how is it formed?
An ionic bond, also known as an electrovalent bond, is a type of chemical bond formed through the complete transfer of one or more electrons from a metal atom to a non-metal atom. This transfer results in the formation of two oppositely charged ions: a positive ion (cation) from the atom that loses electrons and a negative ion (anion) from the atom that gains them. The strong electrostatic force of attraction between these oppositely charged ions constitutes the ionic bond. A classic example is Sodium Chloride (NaCl).
2. What is a covalent bond and how is it formed?
A covalent bond is a chemical bond formed by the mutual sharing of electrons between two atoms, typically non-metals. Instead of transferring electrons, the atoms share one or more pairs of valence electrons to achieve a stable electron configuration, similar to that of a noble gas. The shared pair of electrons is attracted by the nuclei of both atoms, holding them together. Examples include the bond in a water molecule (H₂O) and in chlorine gas (Cl₂).
3. How can you tell if a compound has ionic or covalent bonds?
There are two primary ways to determine the type of bond:
Types of Elements: A bond between a metal and a non-metal is typically ionic. A bond between two non-metal atoms is generally covalent.
Electronegativity Difference: The difference in electronegativity (the ability of an atom to attract shared electrons) between the two atoms is a key indicator. A large difference (usually > 1.7) suggests an ionic bond, while a small difference (usually < 1.7) suggests a covalent bond.
4. Which bond is stronger, an ionic or a covalent bond, and why?
Generally, ionic bonds are stronger than covalent bonds. The reason lies in the nature of the forces involved. Ionic bonds are the result of powerful electrostatic forces of attraction between oppositely charged ions arranged in a well-defined crystal lattice. This non-directional force is very strong. In contrast, a covalent bond involves the sharing of electrons between specific atoms and is a more localised, directional force. Breaking the entire crystal lattice of an ionic compound requires more energy than overcoming the intermolecular forces between individual covalent molecules.
5. What is the fundamental similarity between ionic and covalent bonding?
The most important similarity is their ultimate purpose or goal. Both ionic and covalent bonding are mechanisms that allow atoms to achieve a more stable electron configuration, usually by attaining a full outer shell of electrons (an octet). By either transferring or sharing electrons, atoms lower their overall potential energy and become more stable, forming molecules or compounds.
6. Can a single chemical compound contain both ionic and covalent bonds?
Yes, many compounds, particularly those containing polyatomic ions, feature both types of bonds. A great example is Sodium Hydroxide (NaOH). The bond between the sodium ion (Na⁺) and the hydroxide ion (OH⁻) is ionic. However, within the hydroxide ion itself, the bond between the oxygen (O) and hydrogen (H) atoms is covalent, as they share electrons.
7. How do the real-world properties of ionic and covalent compounds differ?
The type of bonding directly influences a compound's physical properties:
Melting and Boiling Points: Ionic compounds (like salt) have very high melting and boiling points due to the strong forces in their crystal lattice. Covalent compounds (like sugar or water) have much lower melting and boiling points.
Electrical Conductivity: Ionic compounds do not conduct electricity in their solid state but are good conductors when molten or dissolved in water. Covalent compounds are generally poor conductors of electricity in any state.
Physical State: At room temperature, ionic compounds are typically hard, crystalline solids, while covalent compounds can be solids, liquids, or gases.
8. Why don't noble gases like Helium or Argon form ionic or covalent bonds under normal conditions?
Noble gases are chemically inert because they already possess a stable electron configuration. Their outermost electron shell (valence shell) is completely full. As a result, they have no energetic incentive to lose, gain, or share electrons, which is the fundamental driving force behind chemical bonding. Since they are already in a low-energy, stable state, they do not readily react to form bonds with other elements.
