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Dalton's atomic theory
States that matter is composed of extremely small particles called atoms; atoms are invisible and indestructible; atoms of a given element are identical in size, mass, and chemical properties; atoms of a specific element are different from those of another element; different atoms combine in simple whole-number ratios to form compounds; in a reaction, atoms are separated, combined or rearranged.
atom
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.
cathode ray
Radiation that originates from the cathode and travels to the anode of a cathode-ray tube.
electron
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.
nucleus
The extremely small, positively charged, dense center of an atom that contains positively charged protons and neutral neutrons.
proton
A subatomic particle in an atom's nucleus that has a positive charge of 1+.
neutron
A neutral, subatomic particle in an atom's nucleus that has mass nearly equal to that of a proton.
atomic number
The number of protons in an atom.
isotope
Atoms of the same element with different numbers of neutrons.
mass number
The number after an element's name, representing the sum of its protons and neutrons.
atomic mass unit (amu)
One-twelfth the mass of a carbon-12 atom.
atomic mass
The weighted average mass of the isotopes of that element.
radioactivity
The process in which some substances spontaneously emit radiation.
radiation
The rays and particles-alpha and beta particles and gamma rays- that are emitted by radioactive materials.
nuclear reaction
A reaction that involves a change in the nucleus of an atom.
radioactive decay
A spontaneous process in which unstable nuclei lose energy by emitting radiation.
alpha radiation
Radiation that is made up of alpha particles; is deflected toward a negatively charged plate when radiation from a radioactive source is directed between two electrically charged plates.
alpha particle
A particle with two protons and two neutrons, with a 2+ charge; is equivalent to a helium-4 nucleus, can be represented by ꭤ; and is emitted during radioactive decay.
nuclear equation
A type of equation that shows the atomic number and mass number of the particles involved.
beta radiation
Radiation that is made up of beta particles; is deflected toward a positively charged plate when radiation from a radioactive source is directed between two electrically charged plates.
beta particle
A high-speed electron with a 1- charge that is emitted during radioactive decay.
gamma ray
High-energy radiation that has no electrical charge and no mass, is not deflected by electric or magnetic fields, usually accompanies alpha and beta radiation, and accounts for most of the energy lost during radioactive decay.
