Valence Electrons and Chemical Bonding

Ionic Bonding

When atoms combine to form compounds, they give up, accept, or share electrons to assemble an octet in their outer shells. In ionic bonding, an octet forms when valence electrons transfer from one atom to another, resulting in an electrostatic force that holds the ions together. For instance, sodium transfers its $1$ valence electron to fluorine, which has $7$ valence electrons, allowing both to achieve outer shell octets. Consequently, sodium acquires a positive $1$ charge by losing $1$ electron, and fluorine acquires a negative $1$ charge by gaining $1$ electron.

Covalent Bonding

In covalent bonding, valence electrons are shared between atoms to achieve an octet. Two fluorine atoms, each with $7$ valence electrons, share $1$ electron so both reach $8$ valence electrons. Similarly, hydrogen shares its $1$ valence electron with fluorine's $7$ valence electrons, enabling fluorine to achieve an octet and hydrogen to obtain $2$ electrons, which is the stable configuration for the first electron shell.