![[Greek letter] capital gamma](p540.2.jpg){kind=small}
and ionization potential of the most abundant elements.
Roman numerals refer to row in the periodic table, with "III"
including the fourth row. All elements in a band have approximately
the same gravitational energy and vion, as discussed
in secs. 21.4 and 21.5. Minor and trace elements are indicated,
respectively, by parentheses and brackets.