What causes a chemical bond to form between atoms ?

A chemical bond forms between atoms when the outer shell (valence electrons) of one atom interacts with the outer shell of another atom. This interaction is influenced by the principle of electron configuration, which states that atoms tend to achieve a stable electronic configuration similar to that of a noble gas. There are three main types of chemical bonds: covalent bonds, ionic bonds, and metallic bonds.

1. Covalent bonds: In a covalent bond, atoms share electrons in their outer shell. This sharing occurs when two nonmetal atoms with comparable electronegativity values come together to form a molecule. The sharing of electrons allows atoms to complete their valence shells and achieve stability. For example, in a molecule of water (H2O), each hydrogen atom shares its electron with the oxygen atom, resulting in a stable molecule.

2. Ionic bonds: In an ionic bond, electrons are transferred from one atom to another. This occurs when there is a significant difference in electronegativity between two atoms, typically a metal and a nonmetal. The atom with higher electronegativity gains electrons, becoming negatively charged, while the atom with lower electronegativity loses electrons, becoming positively charged. These charged particles are called ions, and they are attracted to each other, forming an ionic bond. Sodium chloride (NaCl) is an example of an ionic compound, where sodium donates an electron to chlorine.

3. Metallic bonds: Metallic bonding occurs in metals, where a "sea" of delocalized electrons is shared between metal cations. The valence electrons of metal atoms are loosely held, which allows them to move freely throughout the structure. This electron mobility gives metals their unique properties, such as malleability and good electrical conductivity.

To summarize, chemical bonds form between atoms when their outer electron shells interact or when electrons are transferred between atoms to achieve stability. The type of bond formed depends on factors such as electronegativity and the nature of the atoms involved.