The three main types of chemical bonds are ionic bonds, covalent bonds, and metallic bonds. The type of bond determines the structure, stability, and properties of a substance.
Chemical bonds can affect the stability of a compound; those with weak chemical bonds are usually less stable. Bonds also dictate the type of reactions that a substance can undergo, as well as the amount of energy involved.
Bonds are central to the study and practice of chemistry. From simple inorganic molecules to complex biochemical compounds, chemical bonds play crucial roles in the behaviours of substances. Metallic bonds, for instance, are produced by delocalised electrons that are spread out through the molecular lattice structure of the metal. This is why metals are very good conductors of electricity.
Understanding the types of chemical bonds is crucial for synthesising chemicals such as dyes, medicines, and biological molecules like hormones. It’s possible to manufacture complex chemicals from simpler chemicals when you know how these smaller molecules react together.
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Ionic bonds, also known as electrovalent bonds, are a type of bond wherein the electrons are transferred from one atom to another atom. That means that one atom becomes positively charged as it loses electrons, while the other atom becomes negatively charged as it gains electrons.
Ionic compounds are most commonly formed between a metal and a non-metal. They typically take the form of a crystalline solid or salt.
Alkali metals like sodium and alkaline earth metals, such as magnesium, have strong affinities with non-metals, particularly fluorine and chlorine.
With the exception of astatine, the four halogens are very strong electrophiles. Below is a list of the five strongest electrophiles, along with the corresponding electrophilicity index.
- Fluorine: 3.86
- Chlorine: 3.67
- Bromine: 3.40
- Iodine: 3.09
- Hypochlorite: 2.52
The metals that form ionic bonds with electrophiles can also be ranked according to their reactivity. This means a more reactive metal can displace a less reactive metal in a substitution reaction.
For example, in the second group of elements in the periodic table, the alkaline earth metals are ranked as follows:
- Beryllium (Be)
- Magnesium (Mg)
- Calcium (Ca)
- Strontium (Sr)
- Barium (Ba)
- Radium (Ra)
The reactivity of these elements increases from top to bottom. Although they all readily donate their electrons to electrophiles, the reactivity increases as the atoms get bigger. As the size increases, the electrons move further from the nucleus. This lessens their attraction to the nucleus and they become increasingly easier to remove.
What Is an Example of an Ionic Bond?
The most familiar example of an ionic bond is the bond between sodium and chlorine in sodium chloride, or table salt.
The ionic bond in sodium chloride is responsible for the crystalline solid structure of this substance. It’s also the reason why a solution of sodium chloride is good at conducting electricity. In fact, our body needs sodium chloride and trace amounts of other electrolytes to function properly.
Are Ionic Bonds Strong?
The ionic bonds in salts are strong due to the strong coulombic attractions between the ions. The opposite charges have strong attractions that require more energy to break compared to other types of bonds.
For example, it requires at least 769 kJ of energy to break the ionic bonds of one mole of sodium chloride. However, it takes only 436 kJ of energy to break the covalent bonds between the atoms of one mole of a diatomic hydrogen molecule.
Many compounds, especially organic compounds and biological molecules, are covalently bonded. This type of bond is the norm between non-metal atoms.
Atoms that are covalently bonded share electrons almost equally. Compounds that have perfectly symmetrical sharing of electrons are non-polar, while those that have slightly asymmetric sharing of electrons are polar. Polar compounds, such as table sugar, can be dissolved in polar solvents like water. Conversely, non-polar compounds can only be dissolved in non-polar solvents, such as in the case of hydrocarbons.
Covalent bonds can either be single, double, or triple bonds. As bonds can be shared by more than two different atoms, molecules that are covalently bonded can form chains and rings. This makes covalent bonds ideal for large and complex organic molecules.
Covalent bonds follow the octet rule, which means the outer shell must have eight electrons to become stable like the noble gases. As a result, molecules with covalently bonded atoms have regular or definite geometric shapes, such as tetrahedral, trigonal, and octahedral. The bond angles are also determined in this way.
What is an Example of a Covalent Bond?
The angle of the bonds between the oxygen atom and the two hydrogen atoms makes water a universal solvent that’s capable of dissolving virtually all polar compounds and ionic compounds.
Are Covalent Bonds Strong?
Although covalent bonds are generally weaker than ionic bonds, they provide stability and complexity to large organic molecules. Covalent bonds are common in many organic substances, such as starches. Large organic molecules require enzymes to be broken down.
As the name suggests, metallic bonding is only present in elemental metals. It binds the metal atoms together into tightly-packed configurations. Consequently, the outermost electron shell of every atom overlaps with the shells of its neighbouring atoms. The electrons are delocalised, allowing them to move freely among the atoms. The non-localised electrons make the metal electrically conductive.
What is an Example of a Metallic Bond?
All metal elements have metallic bonds. As well as electrical conductivity, the bonds can determine many of the other properties of metals.
Metallic bonds are responsible for making metals malleable, for instance, as the nuclei of the atoms can easily shift positions without breaking the bonds. Copper is one of the best examples of metals that exhibit malleability, electrical conductivity, and heat conductivity.
Are Metallic Bonds Strong?
It may seem counterintuitive, but metallic bonds are actually weaker than both covalent and ionic bonds. This is because it takes less energy to break metallic bonds compared to covalent and ionic bonds.
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