Passage: The invariant mass of an electron is approximately 9.109×10−31 kilograms, or 5.489×10−4 atomic mass units. On the basis of Einstein's principle of mass–energy equivalence, this mass corresponds to a rest energy of 0.511 MeV. The ratio between the mass of a proton and that of an electron is about 1836. Astronomical measurements show that the proton-to-electron mass ratio has held the same value, as is predicted by the Standard Model, for at least half the age of the universe.Electrons have an electric charge of −1.602×10−19 coulombs, which is used as a standard unit of charge for subatomic particles, and is also called the elementary charge. This elementary charge has a relative standard uncertainty of 2.2×10−8. Within the limits of experimental accuracy, the electron charge is identical to the charge of a proton, but with the opposite sign. As the symbol e is used for the elementary charge, the electron is commonly symbolized by e−, where the minus sign indicates the negative charge. The positron is symbolized by e+ because it has the same properties as the electron but with a positive rather than negative charge.The electron has an intrinsic angular momentum or spin of 1/2. This property is usually stated by referring to the electron as a spin-1/2 particle. For such particles the spin magnitude is √3/2 ħ. while the result of the measurement of a projection of the spin on any axis can only be ±ħ/2. In addition to spin, the electron has an intrinsic magnetic moment along its spin axis. It is approximately equal to one Bohr magneton, which is a physical constant equal to 9.27400915(23)×10−24 joules per tesla. The orientation of the spin with respect to the momentum of the electron defines the property of elementary particles known as helicity.The electron has no known substructure and it is assumed to be a point particle with a point charge and no spatial extent.The issue of the radius of the electron is a challenging problem of the modern theoretical physics. The admission of the hypothesis of a finite radius...

Question: What is different about an electron charge and a proton?
opposite sign