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A chemical bond is a lasting attraction between atoms, ions, or molecules that enables the formation of chemical compounds. The bond may result from the electrostatic force of attraction between oppositely charged ions as in ionic bonds or through the sharing of electrons as in covalent bonds. The strength of chemical bonds varies considerably; there are “strong bonds” or “primary bonds” such as covalent, ionic, and metallic bonds, and “weak bonds” or “secondary bonds” such as dipole-dipole interactions, the London dispersion force, and hydrogen bonding.
In general, strong chemical bonding is associated with the sharing or transfer of electrons between the participating atoms. The atoms in molecules, crystals, metals, and diatomic gases—indeed most of the physical environment around us—are held together by chemical bonds, which dictate the structure and the bulk properties of matter.
Ions and ionic bonds:
An ionic bond is a type of chemical bond formed through an electrostatic attraction between two oppositely charged ions. Ionic bonds are formed between a cation, which is usually a metal, and an anion, which is usually a nonmetal. Pure ionic bonding cannot exist: all ionic compounds have some degree of covalent bonding. Thus, an ionic bond is considered a bond where the ionic character is greater than the covalent character. The larger the difference in electronegativity between the two atoms involved in the bond, the more ionic (polar) the bond is. Bonds with partially ionic and partially covalent characters are called polar covalent bonds.
Forming ions:
Ions come in two types. Cations are positive ions formed by losing electrons. For instance, a sodium atom loses an electron to become a sodium cation,[ Na +]. Negative ions are formed by electron gain and are called anions. For example anion of chlorine is chloride[Cl-].
When one atom loses an electron and another atom gains that electron, the process is called electron transfer. Sodium and chlorine atoms provide a good example of electron transfer.
Properties of ionic bonds:
- Physical properties of ionic compounds:
Ionic compounds are solids and are hard to break due to the strong force of attraction between the positive and negative ions. However, they break into pieces when pressure is applied. So they are considered brittle.
- Melting and boiling points of ionic compounds: A large amount of energy is required to break the ionic bonds between the atoms. So, they have high melting and boiling points.
- Solubility of ionic compounds: Ionic compounds are generally soluble in polar solvents such as water but the solubility tends to decrease in non-polar solvents such as petrol, gasoline, etc.
Covalent bonds:
Whenever a non-metal combines with another non-metal, sharing of electrons takes place between their atoms, which leads to the formation of a covalent bond. A covalent bond can also be formed between two atoms of the same nonmetal
There are two basic types of covalent bonds: polar and nonpolar.
- Polar covalent bond: In a polar covalent bond, the electrons are unequally shared by the atoms and spend more time close to one atom than the other. Because of the unequal distribution of electrons between the atoms of different elements, slightly positive (δ+) and slightly negative (δ–) charges develop in different parts of the molecule.
- Nonpolar covalent bonds: Nonpolar covalent bonds form between two atoms of the same element, or between atoms of different elements that share electrons more or less equally. For example, molecular oxygen is nonpolar because the electrons are equally shared between the two oxygen atoms.
Properties of covalent bond:
- They are usually crystalline solids.
- They have high melting points and high boiling points.
- They are usually soluble in water but insoluble in organic solvents.
- They conduct electricity when dissolved in water or when melted.
Differences between ionic compounds and covalent compounds
Ionic compounds | Covalent compounds |
They are usually crystalline solids | They are usually liquid or gases. Only some of them are solids |
They conduct electricity when dissolved in water | They do not conduct electricity |
They have high melting points and boiling points. That is, ionic compounds are nonvolatile. | They usually have low melting points and boiling points. That is covalent compounds are usually volatile. |
They are usually soluble in water. | They are usually insoluble in water. |
They are insoluble in organic solvents. | They are soluble in organic solvents. |
Conclusion:
All chemical bonding is due to electrostatic attraction. When atoms combine through chemical bonding, they form compounds’ unique structures composed of two or more atoms. We can say based on our experiment and analysis, that our hypothesis was correct. Ionic compounds can’t conduct electricity, and ionic compounds’ melting point is higher than the covalent compounds’ melting point.
