 | Term | Definition |
| |
atom |
smallest particle of an element that retains its identity in a chemical reaction |
| |
atomic mass |
the weighted average of the masses of the isotopes of an element |
| |
atomic mass unit (amu) |
a unit of mass equal to one-twelfth the mass of a carbon-12 atom |
| |
atomic number |
the number of protons in the nucleus of an atom of an element |
| |
cathode ray |
stream of electrons produced at the negative electrode (cathode) of a tube containing a gas at a low pressure |
| |
Dalton's Atomic Theory |
first to relate chemical changes to events at the atomic level |
| |
electron |
negatively charged subatomic particle |
| |
group |
vertical column of elements in the periodic table; the constituent elements have similiar chemical and physical properties |
| |
isotopes |
atoms of the same element that have the same atomic number but different atomic masses due to a different number of neutrons |
| |
mass number |
total number of protons and neutrons in the nucleus of an atom |
| |
neutron |
a subatomic particle with no charge and a mass of 1 amu; found in the nucleus of an atom |
| |
period |
horizontal row of elements in the periodic table |
| |
periodic table |
an arrangement of elements in which the elements are separated into groups based on a set of repeating properties |
| |
proton |
a positively charged subatomic particle found in the nucleus of an atom |
| |
nucleus |
the tiny, dense central portion of an atom, composed of protons and neutrons |
| |
amplitude |
the height of a wave's crest |
| |
atomic emission spectrum |
pattern formed when light passes through a prism or diffraction grating to separate it into the different frequencies of light it contains |
| |
atomic orbital |
mathematical expression describing the probability of finding an electron at various locations; usually represented by the region of space around the nucleus where there is a high probability of finding an electron |
| |
aufbau principle |
rule that electrons must occupy the orbitals of lowest energy first |
| |
electromagnetic radiation |
energy waves that travel in a vacuum at a speed of 2.998 x 10^8 m/s; includes radio waves, microwaves, infrared waves, visible light, ultraviolet waves, x-rays, and gamma rays |
| |
electron configurations |
arrangement of electrons of an atom in its ground state into various orbitals around the nuclei of atoms |
| |
energy levels |
the specific energies an electron in an atom or other system can have |
| |
frequency |
the number of wave cycles that pass a given point per unit of time; frequency and wavelength are inversely proportional to each other |
| |
ground state |
the lowest possible energy of an electron described by quantum mechanics |
| |
Heisenberg uncertainty principle |
it is impossible to know exactly both the velocity and the position of a particle at the same time |
| |
hertz |
unit of frequency, equal to one cycle per second |
| |
Hund's rule |
electrons occupy orbitals of the same energy in a way that makes the number or electrons with the same spin direction as large as possible |
| |
Pauli exclusion principle |
an atomic orbital may describe at most two electrons, each with opposite spin direction |
| |
photons |
a quantum of light; a discrete bundle of electromagnetic energy that interacts with matter similarly to particles |
| |
quantum |
the amount of energy needed to move an electron from one energy level to another |
| |
quantum mechanical model |
the modern description, primarily mathematical, of the behavior of electrons in atoms |
| |
spectrum |
wavelenghts of visible light that are separated when a beam of light passes through a prism; range of wavelenghts of electromagnetic radiation |
| |
wavelength |
the distance between adjacent crests of a wave |
| Add or remove terms from this set |
