Most objects we know of are empty spaces. The atoms and molecules that make up everyday objects, such as bricks, wood, glass, etc., are usually empty spaces, even if the objects themselves seem durable and solid.
An atom consists of a very dense central nucleus called the nucleus and a cloud of electrons around the nucleus. Depending on the atom being considered, the electron cloud has a radius that is approximately 10,000 times that of the nucleus. If the nucleus were the size of a ping-pong ball, the electron cloud would extend two-tenths of a mile. Most of that distance would be empty.
Although the nucleus is only a very small part of the size of the atom, it makes up the greater part of the atomic weight. The fact that most of the empty space, including objects, is due to the electronic cloud makes it as light as it is. If you had a cup full of nuclei that had their electron clouds stripped so that the nuclei could pack tightly in the cup, that cup of nuclear material would weigh about 50,000,000,000 tons.