Here's why:
* The nucleus is positively charged: The protons in the nucleus carry a positive charge.
* Electrons are negatively charged: Electrons carry a negative charge.
* Opposite charges attract: The positive charge of the nucleus attracts the negative charge of the electrons. This attraction is what keeps the electrons bound to the atom.
It's important to note that the electron's motion around the nucleus is not a simple circular orbit like a planet around a star. It's more complex, involving quantum mechanics and the concept of electron clouds.
