Bonding and valence are two concepts that explain how atoms interact with each other to form molecules. Bonding refers to the forces that hold atoms together in a molecule, while valence describes the number of electrons an atom can share or transfer to other atoms to form bonds.
Atoms form bonds by either sharing electrons with other atoms (covalent bonding) or transferring electrons to other atoms (ionic bonding). Covalent bonds are formed between nonmetal atoms, while ionic bonds are formed between a metal and a nonmetal.
Bonding and valence are crucial concepts in chemistry because they explain how elements combine to form compounds. The type of bond formed between atoms determines the physical and chemical properties of a compound, such as its melting point, boiling point, and reactivity.
The valence of an atom is determined by the number of valence electrons it has. Valence electrons are the outermost electrons in an atom's electron cloud. The group number of an element on the periodic table usually indicates the number of valence electrons it has (e.g. group 1 elements have 1 valence electron).
Sodium (Na) and chlorine (Cl) atoms bond together to form the compound sodium chloride (NaCl). Na has one valence electron and Cl has seven, so they form an ionic bond where Na transfers its electron to Cl. This results in a stable compound with the chemical formula NaCl, which we know as table salt.