chapter 4

the number of protons in an atom

the weighted average mass of the isotopes of that element

a negatively charged, fast-moving particle with an extremely small mass that is found in all forms of matter and moves through the empty space surrounding an atom’s nucleus.

a neutral, subatomic particle in an atom’s nucleus that has a mass nearly equal to that of a proton.

one-twelfth the mass of a carbon-12 atom.

 a ray of radiation that originates from the cathode and travels to the anode of a cathode-ray tube.

atoms of the same element with different numbers of neutrons

the number after an element’s name, representing the sum of its protons and neutrons.

the extremely small, positively charged, dense center of an atom that contains positively charged protons, neutral neutrons, and is surrounded by empty space through which one or more negatively charged electrons move.

the smallest particle of an element that retains all the properties of that element; is electrically neutral, spherically shaped, and composed of electrons, protons, and neutrons.