Chapter 25 Flashcards
Electrons
negatively charged subatomic particles
Cathode ray
glowing beam that traveled from the cathode to the anode
Protons
positively charged sub atomic particles. Each proton has a mass about 1840 times that of an electrom
Neutrons
subatomic particles with no charge buth with a mass nearly equal to that of a proton.
Nucleus
tiny central core of an atom and is composed of protons and neutrons
Atomic number
number of protons in the nucleus of an atom of that element
Mass Number
total number of protons and neutrons in an atom
Isotopes
atoms that have the same number of protons but different numbers of neutrons
Atomic mass unit (amu)
is defined at one twelfth of the mass of a carbon-12 atom
atomic mass of an element
is a weighted average mass of the atoms in a naturally occurring sample of the element. A weighted mass reflects botht he mass and the relatibe abundance of the isotopes as they occur in nature.
How do you calculate atomic mass of an element
multiply the mass of each isotope by its natural abundance, expressed as a decimal and then add the products.
energy levels
the fixed energies an electron can have
quantum of energy
the amount of energy required to move an electron from one energy level to another energy level
quantum mechanical model
is the modern description of the electrons in atoms. determins the allowed energies an electron can have and how likely it is to find the electron in various locations around the nucleus of an atom
atomic orbital
describing the poabability of findinf an electron at various location around the nucleus
electron configurations
the ways in which electrons are arranged in various orbitals around the nuclei of atoms
aufbau principle
electrons occupy the orbitals of lowest energy first
Pauli exclusion principle
an atomic orbital may describe at most two electrons
Spin
a quantum mechanical property of. electrons and may be thought of as clockwise or counterclockwise
Hund’s rule
electrons occupy orbitals of the same energy in a way that makes the number of electrons wiht the same spin directions as large as possible.
Nuclear force
an attractive force that acts between all nuclear particles that are extremely close together, such as protons and neutrons in a nucleus
Band of stability
a plot of neutrons vs. protons for all stable nuclei forms a pattern
Positron
a particle withthe mass of an electron but a positive charge.
Half-life
the time required for one-half of the nuclei in a radioisotope sample to decay to products.
Transmutation
the conversion of an atom of one element into an atom of another element. Transmutation can occur by radioactive decay or when particles bombard the nuceul of an atom.
Transuranium elements
elements with atomic numbers above 92, the atomic number of uranium
Fission
when the nucei of certain isotopes are bombarded with neutrons, the nuclei split into smaller fragments
Neutron moderation
a process that slows down neutrons so the reactor fuel can capture them to continue the chain reaction
Neutron absorption
a process that decreases the number of slow-moving neutrons
Fussion
occurs when nuclei combine to produce a nucleus of greater mass.
ionizing radiation
the radiation emitted by radioisotopes
Atom
the smallest particle of an element that retains its identity in a chemical reaction
Daltons atomic theory
- all elements are composed of tiny indivisible particles called atoms, 2. Atoms of the same element are identical. Atoms of any one element are different from those of any other element. 3. Atoms of different elements can physically mix together or can chemically combine in simple whole number ratios to form compounds. 4. Chemical reactions occur when atoms are separated from eachother, joined or rearranged in a different combination. Atoms of one element are never changed into the atoms of antoher element as a result of a chemical reaction.
