Module 3 Vocabulary

Dalton's Atomic Theory

determined the mass ratios of the elements in chemical reactions (the mass ratio describes how many atoms of each element make up a compound); based on Democritus’s ideas

atom

smallest particle of matter that retains the properties of the element

cathode ray

this ray, originating from the cathode and traveling to the anode

electrons

negatively charged particles that are part of all forms of matter

nucleus

tiny, dense region in the center of the atom that contained almost all of the atom’s positive charge

proton

a subatomic particle carrying a charge equal to but opposite that of an electron

neutron

a subatomic particle that has a mass nearly equal to that of a proton, but carries not electric charge

atomic number

the number of protons in an atom; gives an element its identity

isotopes

atoms with the same number of protons but different numbers of neutrons; gives atoms different mass numbers

mass number

identifies each isotope of an element and is the sum of the atomic number (or number of protons) and neutrons in the nucleus

atomic mass unit (amu)

one twelfth the mass of a carbon-12 atom; approximate mass of a proton or a neutron

atomic mass

the weighted average mass of the isotopes of the element

radioactivity

the process where some substances spontaneously emit radiation to become stable

radiation

the rays and particles emitted by the radioactive material

nuclear reaction

a reaction that involves a change in an atom's nucleus

radioactive decay

the spontaneous process where unstable nuclei lose energy by emitting radiation

alpha radiation

the radiation that was deflected toward the negatively charged plate

alpha particle

contains 2 protons and 2 neutrons, and thus has a 2+ charge, which explains why ___________ are attracted to the negatively charged plate

nuclear equation

shows the atomic numbers and mass numbers of the particles involved (although elements are not conserved, the total number of protons plus neutrons is conserved)

beta radiation

the radiation that was deflected toward the positively charged plate

beta particle

an electron with a 1- charge

gamma ray

high-energy radiation that has no mass and is denoted by the symbol γ

neutral/stable atom

the number of electrons is the same as the number of protons

ion

different number of protons and electrons