The chemical properties of an element depend upon

The chemical properties of an element are primarily determined by its electronic configuration, specifically the number of electrons in its outermost shell, also known as valence electrons [2]. Atoms react with other elements to achieve a stable, completely filled valence shell, similar to the configuration of noble gases [2]. This tendency to gain, lose, or share electrons drives chemical bonding and reactivity [2]. While isotopes of an element have different numbers of neutrons and different mass numbers, they possess the same number of protons and electrons. Consequently, isotopes exhibit nearly identical chemical behavior because their electron arrangements are the same. Physical properties, such as mass and density, may vary with the number of neutrons, but the fundamental chemical identity and reactivity are governed by the valence shell electrons.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 3: Metals and Non-metals > 3.3 HOW DO METALS AND NON-METALS REA ALS REACT? > p. 46
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > 4.1 BONDING IN CARBON – THE COVALENT BOND > p. 59