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 title: 1
 description: 
 published: true
-date: 2026-02-11T15:34:58.131Z
+date: 2026-02-11T15:36:13.726Z
 tags: 
 editor: ckeditor
 dateCreated: 2026-02-11T14:58:54.870Z
@@ -382,5 +382,10 @@ dateCreated: 2026-02-11T14:58:54.870Z
 <p><span style="font-family:Arial, Helvetica, sans-serif;">The electronic configuration of Cr (Chromium) and Cu (Copper) do not follow the order. The outer subshell become half or fully filled to gain extra stability.</span></p>
 <p><span style="font-family:Arial, Helvetica, sans-serif;">It is also because that 4s and 3d energy difference is small.</span></p>
 <p>&nbsp;</p>
+<h3><span style="font-family:Arial, Helvetica, sans-serif;">Periodic table groups</span></h3>
+<p><span style="font-family:Arial, Helvetica, sans-serif;">Group 1 - Alkali metal</span></p>
+<p><span style="font-family:Arial, Helvetica, sans-serif;">Group 2 - Alkaline earth metal</span></p>
+<p><span style="font-family:Arial, Helvetica, sans-serif;">Group 17 (7) - Halogen</span></p>
+<p><span style="font-family:Arial, Helvetica, sans-serif;">Group 18 (8) - Noble gas</span></p>
 <p>&nbsp;</p>
 <p>&nbsp;</p>