. Elements in the s and p blocks of the table are referred to as
typical elements whilst those in the d block are called "transition
elements" and those in the/block are called actinides and lanthanides
(or wrare earth' elements).
5. The table contains vertical groups of elements; each member of
a group having the same number of electrons in the outermost
quantum level. For example, the element immediately before each
noble gas, with seven electrons in the outermost quantum level, is
always a halogen. The element immediately following a noble gas,
with one electron in a new quantum level, is an alkali metal (lithium,
sodium, potassium, rubidium, caesium, francium).
6. The periodic table also contains horizontal periods of elements,
each period beginning with an element with an outermost electron
in a previously empty quantum level and ending with a noble gas.
Periods 1, 2 and 3 are called short periods, the remaining are long
periods; Periods 4 and 5 containing a series of transition elements
whilst 6 and 7 contain both a transition and a 4rare earth' series.