The electrostatic force between opposite charges attracts negatively charged electrons to positively charged protons. This force is given by Coulomb's law, which states that the force between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them.

$$ F = k \frac{|q_1||q_2|}{r^2} $$

Where F is the electrostatic force, k is the electrostatic constant, q_1 and q_2 are the magnitudes of the charges, and r is the distance between the charges.

In the case of an electron and a proton, q_1 = -1.6 × 10^-19 C (the charge of an electron) and q_2 = 1.6 × 10^-19 C (the charge of a proton). The distance between them is typically on the order of 1 × 10^-10 m (the Bohr radius). Plugging these values into Coulomb's law, we get:

$$ F = (9 × 10^9 \frac{N m^2}{C^2}) \frac{(-1.6 × 10^{_19} C)(1.6 × 10^{-19} C)}{(1 × 10^{-10} m)^2} = -2.304 × 10^{−8} N $$

This negative sign indicates that the force is attractive. The magnitude of this force is very small, but it is enough to hold the electron in orbit around the nucleus of an atom.