Yes, it is true that the vast majority of an atom is empty space. Atoms are composed of a central nucleus, which contains positively charged protons and uncharged neutrons, surrounded by a cloud of negatively charged electrons. The size of the nucleus is extremely small compared to the overall size of the atom.
The concept of empty space in an atom arises from the fact that electrons occupy regions of space called orbitals or electron shells, which are like probability clouds where an electron is likely to be found. These electron shells are relatively large compared to the size of the nucleus, resulting in a significant amount of empty space within the atom.
However, it's important to note that this empty space doesn't imply that atoms are devoid of substance or are not "real." The behavior and properties of matter are determined by the interactions between the subatomic particles within the atom, particularly the interactions between electrons and the positively charged nucleus.
Despite the empty space, the forces and interactions within the atom hold it together. Electromagnetic forces between negatively charged electrons and positively charged protons provide the necessary attraction to keep the electrons in orbit around the nucleus. These interactions give rise to the stability of atoms and allow for the formation of molecules and the vast array of matter that we observe in the universe.
So, even though atoms are mostly empty space, their properties and the material substances they form arise from the interactions between the subatomic particles within them.