Chemical bonds are the electrostatic attraction between atoms of different elements, which form a crystal or molecular compound. This happens either through sharing electrons, or the transfer of electrons from one atom to another.
Chemical bonding gives rise to a wide variety of compounds from various combinations of elements. Compounds can range from simple inorganic compounds with only two elements, to complex, large-molecule organic compounds.
Proteins, for example, are long chains (polymers) of repeating units of amino acids. Amino acids are composed of several elements bonded together in specific proportions. For example, the simplest amino acid, glycine, has the chemical formula NH₂‐CH₂‐COOH. Each glycine molecule contains two carbon atoms, five hydrogen atoms, one nitrogen atom, and two oxygen atoms.
Chemical bonds determine the structure and properties of molecules, which are also directly related to the type of elements that are chemically bonded together. The three main types of bonds are covalent, ionic, and metallic bonds.
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How Are Chemical Bonds Used in Chemistry?
Chemical bonds are a useful reference in synthesising specific types of molecules with known chemical and physical properties. By understanding chemical bonds and knowing how to combine chemical units, chemists can synthesise everything from artificial flavours to medicines. They can also use this knowledge to create a variety of useful materials, such as plastics.
Plastics are polymers that are created from repeating units called monomers. Knowing how these units chemically bond together enables chemists to synthesise different types of plastics with various applications. Some of the common types of plastics include:
- Polyethylene terephthalate – also known as a wrinkle-free fibre, this type of plastic is commonly used to manufacture drinks bottles.
- High-density polyethylene – this type of plastic has virtually no branched chains of polymers. It’s dense and strong, which makes it ideal for manufacturing plastic bags, shampoo bottles, juice containers, and medicine bottles.
- Polyvinyl chloride – polyvinyl chloride is commonly used in manufacturing water pipes as well as toys, blood bags, and detergent bottles.
- Low-density polyethylene – from a chemical point of view, this type of plastic is the simplest and easiest to manufacture. It has significant branching, which makes it less dense and less ordered (crystalline). Low-density polyethylene is widely used in manufacturing plastic grocery bags and coatings for paper milk cartons.
- Polypropylene – this type of plastic is considered to be a safer option for food and drink containers because it’s resistant to heat.
- Polystyrene – also known as styrofoam, polystyrene is used in the manufacture of food containers, disposable cups, package protection, insulation, and interior linings of helmets.
What Are the Features of a Chemical Bond?
Various models of chemical bonding have the following features:
- Atoms have a tendency to bond with atoms of different elements. This is because they are more stable when combined with other elements. Alkali metals and halogens are good examples of this.
- The bonding interactions among atoms of different elements are characterised by a specific range of bond energy, which is the minimum energy required to break or create bonds.
- For every type of compound or element combination, there is an optimal distance between the nuclei of the atoms. This is determined by the electrostatic attractions between atoms.
Primary Chemical Bonds
Primary bonds involve the sharing or transferring of electrons between atoms. There are three types of primary bonds – covalent, ionic and metallic bonds.
Covalent bonds are atoms of different elements that are covalently bonded. They generally share valence electrons equally. Although the overall charge is neutral, the compound can be slightly polar due to the bending of the molecule, such as in the case of water.
In an ionic bond, electrons are transferred from one atom to another. As a result, one atom becomes positively charged while the other becomes negatively charged. Ionic compounds are commonly formed when alkali and alkaline earth metals react with non-metal elements.
In solid crystalline form, ionic compounds have a neutral overall charge. This is because the ions are arranged in an alternating regular manner, which cancels the charges. However, when an ionic compound is dissolved in water, the ionic charge difference becomes obvious, especially when subjected to an electrical current.
As the name suggests, metallic bonds mainly occur in metals. In this type of chemical bonding, the electrons become delocalised and are not associated with one particular atom. As a result, they can move freely. This gives metals many of their characteristic properties, such as malleability and good electrical and heat conductivity.
Secondary Chemical Bonds
Secondary chemical bonds do not involve the sharing or transferring of electrons. Instead, these types of bonds occur when there’s an imbalance in the distribution of the charge. The three types of secondary chemical bonding are van der Waals forces, permanent dipole-dipole forces, and hydrogen bonding.
- Van der Waals forces – these are temporary intermolecular forces. They may be caused by a drop in temperature or an increase in pressure, such as in the case of liquified petroleum gas. As the molecules get closer, the intermolecular attraction becomes apparent. There are two types of van der Waals forces: the weak London dispersion forces and the strong but transient dipole-dipole forces.
- Permanent dipole-dipole forces – the attraction between polar water molecules is an example of this type of secondary bonding. In polar molecules, there’s a slight imbalance in the distribution of charges as electrons tend to congregate on one side of the molecule.
- Hydrogen bonding – this refers to a special type of dipole-dipole attraction between molecules. In this type of secondary bonding, a hydrogen atom that is covalently bonded to an atom with strong electronegativity is attracted to another atom that has strong electronegativity. An important example of this is the hydrogen bonding between complementary base pairs in DNA molecules.
Types of Chemical Bonds
As previously discussed, the types of chemical bonds can be generally classified as either primary or secondary bonds. The first category involves the sharing or transferring of electrons. The second category involves the weaker attraction between molecules due to the imbalance in the distribution of charges. You can read more about this in our article ‘What are the Main Types of Chemical Bonds?’.
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