Shell: s-block

 H                                                  He
 Li Be                               .  .  .  .  .  ..
 Na Mg                               .. .. .  .  .. ..
 K  Ca .. .. .  .. .. .. .. .. .. .. .. .. .. .. .. ..
 Rb Sr .  .. .. .. .. .. .. .. .. .. .. .. .. .. .  ..
 Cs Ba .. .. .. .  .. .. .. .. .. .. .. .. .. .. .. ..
 Fr Ra .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
                                                      
       .. .. .. .. .. .. .. .. .. .. .. .. .. ..      
       .. .. .  .. .. .. .. .. .. .. .. .. .. ..      

The s-block consists of elements in Groups 1 and 2 plus Helium. The 
valence electrons of these elements are in the s-shell. This 
spherical shaped shell holds at most 2 electrons, and has an 
azimuthal quantum number of 0. The "s" stands for "sharp".

  1 H  Hydrogen
  2 He Helium
  3 Li Lithium
  4 Be Beryllium
 11 Na Sodium
 12 Mg Magnesium
 19 K  Potassium
 20 Ca Calcium
 37 Rb Rubidium
 38 Sr Strontium
 55 Cs Cesium
 56 Ba Barium
 87 Fr Francium
 88 Ra Radium