What is a Chemical Bond?

A chemical bond is the association of two or more atoms that occurs when they are drawn to one another and combine to form a molecule. This bond acts to hold the atoms together and can be permanent, until it is broken by an outside force or energy. The chemical bond is formed when one atom has less energy than the other, and the attraction between them is strong enough to form a stable compound. The primary bonds include the covalent, ionic, and metallic bonds.

Different Types of Chemical Bonding

1. Ionic Bonding

Ionic bonding is a type of chemical bond that is created when electrons are transferred between a positively charged atom (the cation) and a negatively charged atom (the anion). Typically, this type of interaction occurs between metals and nonmetals. This electron transfer results in the formation of an electrovalent bond between the two ions, causing the cation to become positively charged and the anion to become negatively charged. The cation is formed from the original atom by losing one or more electrons, while the anion is formed from the original atom by gaining one or more electrons. The name of the anion is determined by changing the elemental name with an -ide suffix.

Examples:

• sodium chloride: NaCl, with Na+ and Cl- ions
• lithium nitride: Li3N, with Li+ and N3- ions
• magnesium oxide: MgO, with Mg2+ and O2- ions
• calcium phosphide: Ca3P2, with Ca2+ and P3- ions

Properties of Ionic Bond:

1. Ionic bonds possess a high lattice energy, which is the energy necessary to completely separate the ions in an orderly crystal. This is due to the considerable electrostatic forces between the ions.
2. The strong attractions between the ions result in ionic compounds having high melting and boiling points. It takes a lot of energy to break the bonds and cause the compound to melt or boil.
3. In its solid form, ionic compounds are not good conductors of electricity due to the ions being securely held in a lattice arrangement. However, they become good conductors when in an aqueous solution or molten state. 
4. The strong electrostatic attractions between the ions and the polar water molecules cause many ionic compounds to be soluble in water.

2. Covalent Bonding

The sharing of electrons between atoms is known as covalent bonding. This bonding happens when two atoms of the same or closely related elements in the periodic table come together. Although it can also be seen between nonmetals and metals, this bonding primarily occurs between nonmetals.

Covalent bonds are most likely to form when two atoms have comparable electronegativities or the same affinity for electrons. They share electrons to achieve octet configuration and gain stability because both atoms have the same affinity for electrons, and neither has a strong tendency to donate them. Furthermore, the atom's ionization energy is too high, and its electron affinity is too low for ionic bonding.

For example: Carbon cannot form ionic bonds because it has only four valence electrons or half an octet. Carbon molecules must either gain or lose 4 electrons to form ionic bonds. Since this is very unfavorable, carbon molecules share their four valence electrons through single, double, and triple bonds, allowing each atom to adopt a noble gas configuration. Covalent bonds involve interactions between the sigma and pi orbitals; as a result, covalent bonds lead to the formation of single, double, triple, and quadruple bonds.

Covalent Bonding can be Achieved in two Ways:

1. Sharing of electrons between atoms of the same kind 
• E.g. Formation of H2, Cl2, O2, etc.
2. Sharing of electrons between atoms of different kind 
• E.g. Formation of CH4, H2O, NH3, etc.

Properties of Covalent Bond

If sharing a single electron pair between atoms does not satisfy an atom's normal valence, the atoms may share more than one electron pair. The following are some of the properties of covalent bonds: 

• Covalent bonding does not result in the formation of new electrons. They are only paired together by the bond.
• Extremely strong chemical bonds connect atoms.
• A covalent bond typically contains about 80 kilocalories per mole (kcal/mol) of energy.
• Covalent bonds rarely break on their own after they are formed.
• Covalent bonds are directional, with the bonded atoms showing specific orientations relative to one another.
• Most covalently bound compounds have relatively low melting and boiling points.
• Covalent bonds typically have lower enthalpies of vaporization and fusion.
• Covalently bonded components lack free electrons, which prevents them from conducting electricity.
• Covalent compounds are not soluble in water.

1. Polar Covalent Bond

This type of covalent bond exists when the electronegativity of combining atoms varies significantly, resulting in unequal electron sharing. More electronegative atoms will attract electrons with greater force. Between the atoms, there is an electronegative difference that is greater than 0 but less than 2.0. As a result, the atom will be closer to the shared pair of electrons.

Example: molecules forming hydrogen bonding as a result of an unbalanced electrostatic potential. In this case, the hydrogen atom interacts with electronegative fluorine, hydrogen, or oxygen.

2. Nonpolar Covalent Bond

This type of covalent bond is formed when two atoms share equal electrons. The electronegativity difference between two atoms is zero. It occurs whenever the atoms combined have a similar electron affinity (diatomic elements).

Example: Nonpolar Covalent Bond is found in gas molecules like Hydrogen gas, Nitrogen gas, etc.

3. Metallic

A metallic bond is a particular kind of chemical bond created between positively charged atoms in which the free electrons are distributed among a lattice of cations. Ionic and covalent bonds, on the other hand, develop between two distinct atoms. The primary chemical bond between metal atoms is known as metallic bonding.

Metallic bonds can be found in pure metals, alloys, and some metalloids. For example, the carbon allotrope graphene demonstrates two-dimensional metallic bonding. Even the most refined metals can create chemical bonds between their atoms. For instance, the mercurous ion (Hg22+) can create covalent bonds between metals. Covalent bonds are formed by pure gallium between atom pairs connected to surrounding pairs by metallic bonds.

The factors that affect the strength of a metallic bond include:

• Total number of delocalized electrons.
• Magnitude of positive charge held by the metal cation.
• Ionic radius of the cation

Properties Attributed by Metallic Bonding

Metallic bonds impart several important properties to metals that make them commercially desirable. Some of these properties are briefly described in this subsection.

1. Electrical Conductivity

Electrical conductivity is a measurement of a material's capacity to permit the passage of a charge through it. Any electric current passed through the metal passes through it because the movement of electrons in the electron sea is not constrained, as shown in the illustration below.

The delocalized electrons begin to move in the direction of the positive charge when a potential difference is applied to the metal. Metals are typically effective conductors of electric current because of this.

2. Thermal Conductivity

A material's capacity to conduct or transfer heat is determined by its thermal conductivity. The kinetic energy of the electrons in that region increases when one end of a metallic substance is heated. Through collisions, these electrons impart their kinetic energies to other electrons in the water.

The speed at which kinetic energy is transferred depends on the electrons' mobility. The delocalized electrons are highly mobile because of metallic bonds, which allows them to transfer heat through the metallic substance by crashing into other electrons.

3. Malleability and Ductility

An ionic crystal, such as sodium chloride, breaks into numerous smaller pieces when struck with a hammer. This is due to the crystals' atoms being held together by a rigid lattice that is difficult to deform. The crystal breaks when a force (from the hammer) is applied, fracturing the crystal structure.

The sea of electrons in the metallic bond allows the lattice to deform in the case of metals. As a result, the rigid lattice is deformed rather than fractured when metals are hammered with a hammer. Metals can be beaten into thin sheets because of this. Metals are referred to as being highly ductile because these lattices do not easily fracture.

4. Metallic Luster

Metals are usually shiny or have a metallic luster. Once a certain minimum thickness is reached, they become opaque. Photons are reflected off the smooth surface by the electron sea. The light that can be reflected is restricted to a specific upper frequency.

Metals possess a high density, a high melting point, a high boiling point, and low volatility due to the strong attraction between the atoms in their metallic bonds, which also gives them strength. There are some exceptions. For instance, mercury has a high vapor pressure and is a liquid under normal circumstances. All the metals in the zinc group (Zn, Cd, and Hg) are relatively volatile.

5. High Melting and Boiling Points

The attraction between the metal atoms is substantial due to the solid metallic bonding. A significant amount of energy is required to overcome this force of attraction. This explains why melting and boiling points for metals are frequently high. This does not apply to zinc, cadmium, or mercury (explained by their electron configurations, which end with ns2).

Even when metal is in a molten state, the metallic bond can still be strong. Gallium, for instance, melts at 29.76 C but only boils at 2400 C. As a result, molten gallium is a nonvolatile liquid.