The Pauli exclusion principle states that no two electrons can occupy the same quantum state. This means that the electrons in an atom must be arranged in different shells around the nucleus. The outermost shell of electrons is called the valence shell, and the electrons in this shell are responsible for the chemical bonding between atoms.
When two atoms come close together, their valence electrons interact with each other. If the electrons are attracted to each other, they will form a chemical bond. The type of chemical bond that is formed depends on the number of valence electrons in each atom.
There are three main types of chemical bonds: covalent bonds, ionic bonds, and metallic bonds.
Covalent bonds occur when two atoms share one or more pairs of electrons. The electrons are held in a region of space between the two nuclei, called a molecular orbital. Covalent bonds are the strongest type of chemical bond.
Ionic bonds occur when one atom transfers one or more electrons to another atom. The atoms that gain electrons become negatively charged, while the atoms that lose electrons become positively charged. The oppositely charged ions are then attracted to each other. Ionic bonds are weaker than covalent bonds.
Metallic bonds occur when the valence electrons of metal atoms are delocalized, meaning that they are not associated with any particular atom. The delocalized electrons form a "sea" of electrons that flows throughout the metal. Metallic bonds are weaker than covalent bonds, but they are stronger than ionic bonds.
The interactions between atoms and their electrons are what give objects their physical properties. The strength of the chemical bonds between atoms determines how hard or soft an object is, and the arrangement of the atoms determines its shape and density.
