Chemistry – Atoms, elements and compounds - Atomic structure and the Periodic Table | e-Consult

The electronic configuration of an element, particularly the number of valence electrons (electrons in the outermost shell), largely determines its reactivity. Elements tend to react to achieve a stable octet of electrons, often by gaining, losing, or sharing electrons.

Reactivity and Valence Electrons:

• Elements with few valence electrons (e.g., alkali metals like Sodium) readily lose these electrons to form positive ions, making them highly reactive metals.
• Elements with nearly full valence shells (e.g., halogens like Chlorine) readily gain electrons to form negative ions, making them highly reactive non-metals.
• Elements with a full valence shell (e.g., Noble gases like Neon) are very stable and unreactive.

Similar Reactivity in Groups:

Elements in the same group (vertical column) of the periodic table have the same number of valence electrons. This is because they have the same number of electron shells. Therefore, they have similar tendencies to gain, lose, or share electrons to achieve a stable octet. For example, all alkali metals (Group 1) are highly reactive because they all have one valence electron and readily lose it to form +1 ions. Similarly, all halogens (Group 17) are highly reactive because they all have seven valence electrons and readily gain one electron to form -1 ions.