chem notes, periodic table

• The periodic table is arranged in order of increasing proton (atomic) number
• Periods in the periodic table represent the number of electron shells, with each horizontal row being a period
• Groups in the periodic table represent vertical columns, with elements in the same group having the same number of valence electrons
• Proton number increases by 1 from left to right across a period, while valence electrons also increase by 1 in the same direction
• The metallic character (tendency of a metal atom to lose electrons) decreases across a period, while the non-metallic character (tendency of a non-metal atom to gain electrons) increases
• Metallic character increases down a group (column) in the periodic table, while the number of electron shells increases
• Valence electrons remain the same within a group in the periodic table
• In Group 1, elements are alkali metals with 1 valence electron; Group 17 consists of halogens with 7 valence electrons; Group 18 includes noble gases with 8 valence electrons