Final answer:
Electrons are held in an atom by the attractive electromagnetic force to the positively charged nucleus. They occupy orbitals around the nucleus based on their energy levels, depicted by the electron cloud model rather than fixed orbits.
Step-by-step explanation:
Electrons are held in an atom by attraction to the nucleus, which is at the center of the atom. This attraction is due to the electromagnetic force between the negatively charged electrons and the positively charged protons within the nucleus. The concept often depicted of electrons orbiting the nucleus similar to planets orbiting the sun is a simplified model and doesn't accurately represent the quantum mechanical nature of electrons. In truth, electrons occupy regions of space known as orbitals around the nucleus, determined by their energy levels, which is better visualized using the idea of an electron cloud. The electron cloud model represents the probability of finding an electron in a particular location around the nucleus at any given time, with varying densities indicative of how likely it is to find an electron in a certain area.