A chemical bond is a lasting attraction between these 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. Therefore, the electromagnetic force plays a major role in determining the internal properties of most objects encountered in daily life.
- Ionic bond. An ionic bond is a chemical bond, in which one or more electrons are wholly transferred from an atom of one element to the atom of the other, and the elements are held together by the force of attraction due to the opposite polarity of the charge. This type of chemical bond is typical between elements with a large electronegativity difference.
- Covalent bond. A covalent bond is a chemical bond formed by shared electrons. Valence electrons are shared when an atom needs electrons to complete its outer shell and can share those electrons with its neighbor. The electrons are then part of both atoms and both shells are filled.
- Metallic bond. A metallic bond is a chemical bond, in which the atoms do not share or exchange electrons to bond together. Instead, many electrons (roughly one for each atom) are more or less free to move throughout the metal, so that each electron can interact with many of the fixed atoms.
An ionic bond is a chemical bond, in which one or more electrons are wholly transferred from an atom of one element to the atom of the other, and the elements are held together by the force of attraction due to the opposite polarity of the charge. This type of chemical bond is typical between elements with a large electronegativity difference (i.e. elements situated at the horizontal extremities of the periodic table). An ionic bond is always found in compounds composed of both metallic and nonmetallic elements. There is no precise value that distinguishes ionic from covalent bonding, but an electronegativity difference of over 1.7 is likely to be ionic while a difference of less than 1.7 is likely to be covalent.
Ionic bonding leads to separate positive and negative ions. In the process, all the atoms acquire stable or inert gas configurations (i.e., completely filled orbital shells) and, in addition, an electrical charge – that is, they become ions. For example, common table salt is sodium chloride. Sodium chloride (NaCl) is the classic ionic material. A sodium atom can assume the electron structure of neon by a transfer of its one valence 3s electron to a chlorine atom. After such a transfer, the chlorine ion acquires a net negative charge, an electron configuration identical to that of argon; it is also larger than the chlorine atom. These ions are then attracted to each other in a 1:1 ratio to form sodium chloride (NaCl).
Na + Cl → Na+ + Cl− → NaCl
Ionic compounds conduct electricity when molten or in solution, typically as a solid. Ionic compounds generally have a high melting point, depending on the charge of the ions they consist of. The higher the charges the stronger the cohesive forces and the higher the melting point. They also tend to be soluble in water; the stronger the cohesive forces, the lower the solubility.
A metallic bond is a chemical bond, in which the atoms do not share or exchange electrons to bond together. Instead, many electrons (roughly one for each atom) are more or less free to move throughout the metal, so that each electron can interact with many of the fixed atoms. The free electrons shield the positively charged ion cores from the mutually repulsive electrostatic forces that they would otherwise exert upon one another; consequently, the metallic bond is nondirectional in character. Metallic bonding is found in metals and their alloys. The free movement or delocalization of bonding electrons leads to classical metallic properties such as luster (surface light reflectivity), electrical and thermal conductivity, ductility, and high tensile strength.
Metal is a material (usually solid) comprising one or more metallic elements (e.g., iron, aluminum, copper, chromium, titanium, gold, nickel), and often also nonmetallic elements (e.g., carbon, nitrogen, oxygen) in relatively small amounts. The unique feature of metals as far as their structure is concerned is the presence of charge carriers, specifically electrons. This feature is given by the nature of metallic bond. The electrical and thermal conductivities of metals originate from the fact that their outer electrons are delocalized.