What do they look like? Tree swallows are small birds (about 14 cm long) with long wings and small legs and feet. They are irridescent greenish-blue on their head, shoulders and back, and white their chin, breast and belly. Tree swallows have a short black beak and dark brownish feet.
Ernest Rutherford concluded that an atom contains a very small, dense center, called a nucleus, with a positive charge as a result of his gold foil experiment.
In the center of every atom is a tiny, dense nucleus. The nucleus contains two kinds of particles: neutrons, which have no charge, and positively charged protons. These orbitals surrounding the nucleus have different levels of energy - the farther away each is from the nucleus, the more energy it has.