Chapter 4 (The Structure of an Atom)

Dalton's atomic theory

states that matter is composed of extremely small particles called atoms; atoms are invisible and indestructable; 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 chemical reaction, atoms are separated, combined, or rearranged

atom

the smallest particle of an element that retains the properties of the element

cathode ray

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

electrons

negatively charged particles that are part of all forms of matter

nucleus

the tiny, dense region in the center of the atom where almost all of the atom's positive charge and almost all of its mass are contained

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 a 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 2+ charge; is equivalent to a helium-4 nucleus and is emitted during radioactive decay

nuclear equation

a type of 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 electronically 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