44 terms

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the smallest unit of an element that maintains the properties of that element.
Democritus's Atomic Theory
The universe made of invisible units called atoms.
John Dalton's Atomic Theory
All atoms of a given element were exactly alike and atoms cannot be divided
An atom's central region, which is made up of protons and neutrons
A subatomic particle that has a positive charge and that is found in the nucleus of the atom
A subatomic particle that has no charge and that is found in the nucleus of an atom
A subatomic particle that has a negative electric charge
Bohr's Model of the Atom
This model says that electrons behave more like waves on a vibrating string than like particles.
Energy level
the energy state of an atom
A region in an atom where there is a high probability of finding electrons
valence electron
An electron that is found in the outermost shell of an atom and that determines the atom's chemical properties
Periodic Law
The law taht states that the repeating chemical and physical properties of elements change periodicallly with the atomic numbers of the elements
Dimitri Mendeleev
Russian scientist that created the perodic table according to atomic mass
Periods or series
In chemistry,a horizontal row of eleements in the periodic table.
Groups or families
A vertical column of elements in the periodic table (also called family); elements in a group share chemical properties
Atomic Number (Z)
The number of protons in the nucleus of an atom; the atomic number is the same for all atoms of an element.
Mass number (A)
The sum of the numbers of protons and neutrons in the nucleus in an atom
an atom that has the same number of protons as other atoms of the same element do but that has a different number of neutrons
Atomic mass unit (AMU)
A unit of mass that describes the mass of an atom or molecule; it is exactly one-twelfth of the mass of a carbon atom with mass number 12 (abbreviation,amu)
Avg. atomic mass
the weighted average of the masses of all naturally occuring isotopes of an element
an element that is shiny and that conducts heat and electricity well
an element or compound that conducts electric current better than an insulator but does not as well as a conductor does.
An element that conducts heat and electricity poorly
an element or compound that conducts electric current better than an insulator but does not as well as a conductor does
alkali metals
one of the elements of group 1 of the periodic table
alkali earth metals
one of the elements of group 2 of the periodic table
transition metals
one of the elements of groups 3-12 of the periodic table
one of the elements of group 17 of the periodic table
noble gas
an unreactive element of group 18 of the periodic table
the SI base unit used to measure the amount of a substance whose number of particles is the same as the number of atoms of carbon in 12 g of carbon-12
Avogadro's constant
equals 6.022 X 10 ^23/mol; the number of particles in 1 mol
molar mass
the mass in grams of 1 mol of a substance
the process by which an unstable nucleus emits one or more particles or energy in the form of electromagnetic radiation
nuclear radiation
the particles that are released from the nucleus during radioactive decay,such as neutrons,electrons,and photons
alpha particle
a positively charged atom that is released in the disintegration of radioactive elements and that constsist of two protons and two neutrons
beta particle
a charged electron emitted during certain types of radioactive decay,such as beta decay
gamma ray
the high-energy photon emitted by a nucleus during fission and radioactive decay
the time required for half of a sample of a radioactive substance to disintegrate by radioactive decay or by natural processes
strong nuclear force
the interaction that binds nucleons together in a nucleus
nuclear fission
the process by which a nucleus splits into two or more fragments and releases neutrons and energy
the quantity of ionizign radiation that does as much damage to human tissue as 1 roentgen of high-voltage X rays does
nuclear fusion
the process in which light nuclei combine at extremely high temepratures,forming heavier nuclei and releasing energy
radioactive tracer
a radioactive materail that is added toa substance so that its distribution can be detected later
radon gas
colorless and inertproduced by the radioactive decay of uranium-238 present in soil and rock.Emit alpha and beta particles and gamma rays.