Period 6 element
A chemical element in the sixth row of the periodic table, from cesium through radon. This row includes the lanthanides between barium and hafnium.
Periodic table: A tabular arrangement of chemical elements ordered by atomic number and recurring chemical properties. Period 6 is one of the table’s seven horizontal rows.
Aufbau principle: A model for electron configurations in which lower-energy atomic orbitals are occupied before higher-energy ones. Its orbital-filling order accounts for the sequence of elements across period 6.
Platinum-group metals: Six transition metals—ruthenium, rhodium, palladium, osmium, iridium, and platinum—with related chemical properties. Five members occur in period 6 and are valued for catalysis and corrosion resistance.
Period 5 element: A chemical element in the fifth row of the periodic table, from rubidium through xenon. Its neighboring row lacks a lanthanide series and has fewer elements.
Period (chemistry): A horizontal row in the periodic table, whose elements have electrons occupying the same highest principal shell. A period is the organizing unit that defines this group of elements.
4f orbital: An atomic orbital in the fourth principal shell with angular momentum quantum number three. The 4f subshell fills across the lanthanide portion of period 6.
Gold: A dense, malleable transition metal with atomic number 79 and symbol Au. This period 6 element is used in electronics, jewelry, and monetary reserves.
Period 7 element: A chemical element in the seventh row of the periodic table, from francium through oganesson. The next row contains actinides and substantially more radioactive elements.
Electron shell: A set of atomic orbitals grouped by principal quantum number around an atom’s nucleus. The sixth shell is filled across this period, with subshell-filling exceptions.
Lanthanide contraction: The progressive decrease in atomic and ionic radii across the lanthanides as nuclear charge increases. It shapes the sizes and chemistry of elements following the lanthanides.