Introduction
Chemical bonding is one of the most important topics in chemistry because it explains how atoms combine to form different substances. Almost everything around us, including water, table salt, sugar, metals and gases, is made up of atoms held together through chemical bonds. Two major types of chemical bonding that students encounter in chemistry are ionic bonding and covalent bonding.
Although both types of bonding help atoms form more stable chemical structures, they differ in how they are formed, the particles involved and the properties of the substances they produce. For example, common table salt (sodium chloride, NaCl) is formed through ionic bonding, while water (H2O), methane (CH4) and carbon dioxide (CO2) contain covalent bonds.
Related Topics
* What is chemical combination?
Understanding the differences between ionic and covalent bonding is essential for students preparing for secondary-school chemistry examinations, including WAEC, NECO, JAMB and other science examinations.
In this article, we will explain the meaning of ionic and covalent bonding, how each type is formed, their properties, examples and the major differences between them.
1. What Is Chemical Bonding?
Chemical bonding is the force of attraction that holds atoms or ions together in a chemical substance. Atoms combine through chemical bonding because the resulting arrangement can be more stable and have a lower energy than the separate atoms.
The two major types of bonding discussed in this lesson are:
1. Ionic bonding.
2. Covalent bonding.
To understand their differences, let us first examine each type of bonding.
2. What Is Ionic Bonding?
Ionic bonding is a type of chemical bonding formed through the electrostatic attraction between positively and negatively charged ions. It commonly occurs when electrons are transferred from one atom to another, usually between a metal and a non-metal. The atom that loses electrons becomes a positively charged ion called a cation, while the atom that gains electrons becomes a negatively charged ion called an anion.
The opposite charges attract each other, producing an ionic bond. This type of bonding is also known as electrovalent bonding.
How Is Ionic Bonding Formed?
Ionic bonding generally involves three important stages:
1. One atom loses one or more electrons.
2. Another atom gains those electrons.
3. The resulting oppositely charged ions attract each other through electrostatic forces.
Let us use sodium chloride (NaCl), commonly known as table salt, to explain the formation of an ionic bond.
Example: Formation of Sodium Chloride (NaCl)
Sodium has an atomic number of 11, while chlorine has an atomic number of 17. Their electronic configurations are:
- Sodium (Na): 2,8,1
- Chlorine (Cl): 2,8,7
Sodium has one electron in its outermost shell, while chlorine has seven.
Sodium can achieve a stable electronic arrangement by losing one electron. Chlorine can achieve a stable octet by gaining that electron.
Step 1: Sodium loses one electron.
Na → Na+ + e+
Sodium changes from:
2,8,1 → 2,8
It becomes a positively charged sodium ion (Na+).
Step 2: Chlorine gains one electron.
Cl + e- → Cl-
Chlorine changes from:
2,8,7 → 2,8,8
It becomes a negatively charged chloride ion (Cl-).
Step 3: The ions attract each other.
The positively charged sodium ion and negatively charged chloride ion attract each other through electrostatic forces.
This produces sodium chloride.
Na+ + Cl- → NaCl
The overall chemical reaction is:
2Na + Cl2 → 2NaCl
Important: Sodium chloride does not consist of separate NaCl molecules. In the solid state, its ions form an extended three-dimensional ionic crystal lattice. The formula NaCl represents the simplest ratio of sodium ions to chloride ions.
Other Examples of Ionic Compounds
Ionic compound | Position ion | Negative ion |
Sodium chloride | Na+ | Cl- |
Magnesium oxide | Mg+ | O- |
Calcium chloride | Ca2+ | Cl- |
3. What Is Covalent Bonding?
Covalent bonding is a type of chemical bonding in which two atoms share one or more pairs of electrons. It commonly occurs between non-metal atoms.
Unlike ionic bonding, where electrons are transferred from one atom to another, covalent bonding involves the sharing of electron pairs between atoms.
The shared electrons are attracted to the nuclei of both atoms, holding them together.
How Is Covalent Bonding Formed?
Covalent bonding takes place when atoms share electrons to achieve a more stable electronic arrangement. The process generally involves the following steps:
1. Two atoms approach each other.
2. Their outermost electron shells interact.
3. Each atom contributes electrons to one or more shared pairs.
4. The shared electrons are attracted to both nuclei.
5. A covalent bond is formed.
Example 1: Formation of Hydrogen Molecule (H2)
A hydrogen atom has one electron in its outermost shell.It requires one additional electron to achieve a stable duplet arrangement.When two hydrogen atoms combine, each contributes one electron to form a shared pair.
H: + : H → H:H
The two atoms share one pair of electrons, forming a single covalent bond.
Example 2: Formation of Water (H2O)
Oxygen has an electronic configuration of 2,6 and requires two additional electrons to complete its octet. Each hydrogen atom contributes one electron to form a shared pair with oxygen. As a result, oxygen forms two single covalent bonds with two hydrogen atoms.
H-O-H
Example 3: Formation of Methane (CH4)
Carbon has an electronic configuration of 2,4 and requires four additional electrons to complete its octet.It shares one electron with each of four hydrogen atoms.
Other Examples of Covalent Substances
Substance | Chemical formula | Type of bonding |
Hydrogen | H2 | Single covalent |
Oxygen | O2 | Double covalent |
Nitrogen | N2 | Triple covalent |
Water | H2O | Polar covalent |
Methane | CH4 | Covalent |
Hydrogen Chloride | HCl | Polar covalent |
4. Major Differences Between Ionic and Covalent Bonding
Although ionic and covalent bonding both hold particles together, they differ in several important ways.
The following table summarises their major differences.
Features | Ionic bonding | Covalent bonding |
Meaning | Attraction between oppositely charged ions | Share of electron pairs between atoms |
Formation | Usually involves electron transfer | Involves sharing of electrons |
Common elements | Usually metals and non-metals | Usually non netals |
Particles involved | Positive and negative ions | Atoms |
Electrical charge | Produces cation and anion | Does not contain ions |
Structure | Usually forms giant ionic lattices | May form simple molecules or giant covalent networks |
Melting point and boiling point | High | Often low for simple molecular but high for giant covalent structures |
Electrical conductivity | Conduct electricity in molten or in solution | Poor conductors except graphite |
Solubility in water | Many are soluble but few insoluble ones | Depends on molecular polarity and interactions with water |
Physical state | Solids at room temperature | Can be gaseous, liquid or solids |
Examples | Sodium chloride, magnesium oxide, calcium chloride etc. | Water, mathane, carbon (IV)oxide etc. |
Let us examine some of these differences in greater detail.
5. Differences in the Formation of Ionic and Covalent Bonds
The most important difference between ionic and covalent bonding is the way electrons are involved in their formation.
Ionic Bonding: Transfer of Electrons
In ionic bonding, one atom loses electrons while another gains them. For example, sodium transfers one electron to chlorine to form Na+ and Cl- ions. The electrostatic attraction between the oppositely charged ions produces the ionic bond.
Covalent Bonding: Sharing of Electrons
In covalent bonding, atoms share one or more pairs of electrons. For example, two hydrogen atoms share one pair of electrons to form H2. The shared electrons are attracted to both nuclei, holding the atoms together.
6. Differences in the Physical Properties of Ionic and Covalent Compounds
The type of chemical bonding present in a substance influences its physical properties. However, it is important to remember that covalent substances include both simple molecular substances and giant covalent structures. Their properties can therefore vary considerably.
A. Melting and Boiling Points
Ionic compounds:
Most ionic compounds have high melting and boiling points because strong electrostatic attractions hold their oppositely charged ions together in a crystal lattice. A large amount of energy is needed to overcome these attractions. For example, sodium chloride has a melting point of approximately 801°C.
Simple molecular covalent substances:
Many simple molecular substances have relatively low melting and boiling points because the forces between their molecules are weaker than the ionic attractions in an ionic crystal. Examples include methane and oxygen.
Giant covalent substances:
Diamond and silicon dioxide have very high melting points because their atoms are joined by strong covalent bonds throughout an extended network.
B. Electrical Conductivity
Electrical conductivity is another important difference.
Ionic compounds:
Ionic compounds conduct electricity when molten or dissolved in water, provided that mobile ions are present. This happens because their ions are free to move and carry electrical charges. However, solid ionic compounds do not normally conduct electricity because their ions are fixed in position within the crystal lattice.
Covalent compounds:
Most simple molecular covalent substances do not conduct electricity because they do not contain freely moving charged particles. However, there are exceptions. Graphite, for example, conducts electricity because it contains delocalised electrons that can move through its structure.
C. Solubility in Water
Ionic compounds:
Many ionic compounds dissolve in water because polar water molecules attract and surround their ions. However, not all ionic compounds are soluble. Examples of poorly soluble ionic compounds include silver chloride (AgCl) and barium sulphate (BaSO4).
Covalent compounds:
The solubility of covalent compounds depends on their polarity and the nature of the solvent. Polar covalent compounds such as ammonia and ethanol can dissolve in water while non-polar substances such as methane and oils generally have very low solubility in water.
D. Hardness and Brittleness
Ionic compounds:
Many ionic solids are hard but brittle. When a force shifts the layers of ions in an ionic crystal, ions with similar charges can become aligned. Their strong repulsion can cause the crystal to fracture.
Covalent compounds:
Simple molecular covalent solids are often relatively soft. However, giant covalent structures such as diamond are extremely hard because of their strong three-dimensional network of covalent bonds. Graphite is an exception: it is relatively soft because its layers can slide over one another.
7. Why Do Ionic Compounds Have High Melting Points?
This is a common chemistry examination question. Ionic compounds contain positively and negatively charged ions arranged in a crystal lattice.The ions are held together by strong electrostatic attractions. A large amount of thermal energy is required to overcome the attractions sufficiently to allow the solid to melt. This explains why many ionic compounds have high melting points.
8. Why Do Simple Covalent Compounds Have Low Melting and Boiling Points?
Many simple covalent compounds consist of small, separate molecules. Although the covalent bonds within each molecule are strong, the forces between the molecules are generally weaker.
During melting or boiling, these intermolecular forces are overcome rather than the covalent bonds within the molecules.
Therefore, relatively little energy is often required to melt or boil simple molecular covalent substances.
Remember: This explanation applies mainly to simple molecular covalent substances, not giant covalent structures such as diamond and silicon dioxide.
9. Similarities Between Ionic and Covalent Bonding
Despite their differences, ionic and covalent bonding have some similarities.
1. Both are types of chemical bonding.
2. Both help form stable chemical substances.
3. Both involve the valence electrons of atoms.
4. Both involve electrostatic attractions.
5. Both influence the physical and chemical properties of substances.
6. Both play important roles in chemical reactions and the formation of compounds.
10. Examples of Ionic and Covalent Substances in Everyday Life
Ionic and covalent substances are found in many everyday materials and biological processes.
Examples of Ionic Substances
1. Sodium chloride (NaCl): Common table salt used in food preparation and preservation.
2. Calcium carbonate (CaCO3): Found in limestone, chalk and marble. It is used in cement production and construction.
3. Magnesium oxide (MgO): Used in heat-resistant materials because of its high melting point.
4. Potassium chloride (KCl): Used in fertilisers and other industrial applications.
Examples of Covalent Substances
1. Water (H2O): Essential for life and many biological processes.
2. Carbon dioxide (CO2): Used by plants during photosynthesis.
3. Methane (CH4): An important fuel used for cooking and electricity generation.
4. Glucose (C6H12O6): An important source of energy in living organisms.
5. Ethanol (C2H5OH): Used as a solvent, disinfectant and in some fuel mixtures.
11. How to Identify Ionic and Covalent Compounds
Students are often required to identify whether a compound is ionic or covalent from its chemical formula.
The following guidelines are useful:
Ionic Compounds
An ionic compound commonly contains a metal combined with a non-metal.
Examples:
- NaCl – sodium and chlorine.
- MgO – magnesium and oxygen.
- CaCl2 – calcium and chlorine.
- MgBr2 – magnesium and bromine.
Ionic compounds can also contain polyatomic ions. For example:
- NH4Cl – ammonium chloride.
- Na2SO4 – sodium sulphate.
- CaCO3 – calcium carbonate.
Covalent Compounds
Covalent compounds commonly contain only non-metal elements.
Examples:
- H2O – hydrogen and oxygen.
- CO2 – carbon and oxygen.
- NH3 – nitrogen and hydrogen.
- CH4 – carbon and hydrogen.
Important examination note: These are useful introductory guidelines, not absolute rules. Some compounds have mixed ionic and covalent bonding. For example, ammonium chloride contains ionic attraction between NH4+ and Cl- ions, but covalent bonds within the ammonium ion.
12. Examination Questions and Answers
Test your understanding of ionic and covalent bonding with these questions.
Objective Questions
1. Which of the following best describes ionic bonding?
A. Sharing of electrons between atoms.
B. Transfer of protons between atoms.
C. Electrostatic attraction between oppositely charged ions.
D. Sharing of neutrons between atoms.
Correct answer: C
Explanation: Ionic bonding is the electrostatic attraction between oppositely charged ions.
2. Which of the following compounds is covalent?
A. NaCl
B. MgO
C. CaCl2
D. CH4
Correct answer: D
Explanation: Methane (CH4) is formed through covalent bonding between carbon and hydrogen atoms.
3. An ionic compound conducts electricity when molten because:
A. Its atoms become smaller.
B. Its ions become free to move.
C. Its electrons disappear.
D. Its molecules become neutral.
Correct answer: B
Explanation: In the molten state, the ions are mobile and can carry electrical charges.
4. Which of the following substances contains a triple covalent bond?
A. H2
B. O2
C. N2
D. Cl2
Correct answer: C
Explanation: Nitrogen atoms share three pairs of electrons to form N2.
5. Why do many simple molecular covalent substances have low boiling points?
A. They contain no electrons.
B. Their atoms are held together by ionic bonds.
C. The forces between their molecules are relatively weak.
D. They contain only positive ions.
Correct answer: C
Theory Questions
1. Define ionic bonding and covalent bonding.
2. Explain how sodium chloride is formed through ionic bonding.
3. Describe the formation of a water molecule through covalent bonding.
4. State five differences between ionic and covalent compounds.
5. Explain why solid sodium chloride does not conduct electricity, but molten sodium chloride does.
6. Give three examples each of ionic and covalent compounds.
7. Explain why diamond has a high melting point while methane has a low boiling point.
13. Frequently Asked Questions
What is the main difference between ionic and covalent bonding?
The main difference is that ionic bonding involves electrostatic attraction between oppositely charged ions, usually formed following electron transfer, while covalent bonding involves the sharing of electron pairs between atoms.
Is NaCl ionic or covalent?
Sodium chloride (NaCl) is an ionic compound. Sodium transfers an electron to chlorine, producing Na+ and Cl- ions that attract each other.
Is water ionic or covalent?
Water (H2O) is a covalent compound. Oxygen shares electron pairs with two hydrogen atoms. Its O–H bonds are polar covalent bonds.
Why do ionic compounds conduct electricity when dissolved in water?
When an ionic compound dissolves in water, its ions may separate and become mobile. These moving ions carry electrical charges through the solution.
Why do covalent compounds generally not conduct electricity?
Most simple molecular covalent compounds do not have freely moving ions or electrons to carry electrical charges.
Can two non-metals form an ionic bond?
Ionic bonding is most commonly associated with electron transfer between metals and non-metals. However, the nature of chemical bonding exists on a continuum, and it is not always possible to classify every bond as purely ionic or purely covalent.
Conclusion
Ionic and covalent bonding are two fundamental types of chemical bonding that explain how atoms combine to form different substances.
Ionic bonding involves the electrostatic attraction between oppositely charged ions, commonly formed when electrons are transferred from one atom to another. Covalent bonding, on the other hand, involves the sharing of electron pairs between atoms.
These differences influence the physical and chemical properties of the substances formed, including their melting points, boiling points, electrical conductivity, solubility and physical structures.
A good understanding of ionic and covalent bonding will make it easier to study other chemistry topics such as chemical reactions, molecular structures, valency, electron configuration and the properties of compounds.
Continue reading Chemical combination
.png)
0 Comments