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Atom

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

Nucleus

An atom's central region, which is made up of protons and neutrons

Proton

A subatomic particle that has a positive charge and that is found in the nucleus of the atom

Neutron

A subatomic particle that has no charge and that is found in the nucleus of an atom

Electron

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

Orbital

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

Isotope

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

Metal

an element that is shiny and that conducts heat and electricity well

Metalloid

an element or compound that conducts electric current better than an insulator but does not as well as a conductor does.

Nonmetal

An element that conducts heat and electricity poorly

semiconductor

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

halogens

one of the elements of group 17 of the periodic table

noble gas

an unreactive element of group 18 of the periodic table

mole

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

radioactivity

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

half-life

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

rem

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.

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