Here's why:
* Charge is a fundamental property of particles: Just like mass or spin, charge is an intrinsic property of particles. Electrons are defined by having a negative charge.
* Quantization of charge: Electric charge comes in discrete units, and the charge of an electron is the smallest unit of negative charge.
* Conservation of charge: The total electric charge in a closed system always remains constant. Electrons can't "lose" their negative charge.
Important Note: While electrons always have a negative charge, they can behave differently depending on their environment. For example, in a material, an electron's charge can be partially neutralized by the influence of nearby atoms. However, the electron itself still retains its fundamental negative charge.
