Assertion: metal's electron | /r/HasProperty | period
Facets:
Source sentences:
text: e.g. 2 electrons in shell 1 (period 1, 2 elements H to He), 8 in shell 2 (period 2, 8 elements Li to Ne), there is a sub–level which allows an extra 10 elements (the transition metals) in period 4 (18 elements, K to Kr).