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.
A negatively charged particle within an atom is called an electron. Electrons were discovered in 1897 by a British scientist named J.J.... A negatively charged particle within an atom is called an electron. Electrons were discovered in 1897 by a British scientist named J.J. Thomson. All of the electrons found in an atom balance out the protons of the atom.