20  Calcium

 H                                                  He
 Li Be                               B  C  N  O  F  Ne
 Na Mg                               Al Si P  S  Cl Ar
 K [Ca]Sc Ti V  Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
 Rb Sr Y  Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I  Xe
 Cs Ba La Hf Ta W  Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
 Fr Ra Ac Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og
                                                      
       Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu      
       Th Pa U  Np Pu Am Cm Bk Cf Es Fm Md No Lr      

+--------------------+
| 20   ____          |
|     / ___|__ _     |
|    | |   / _` |    |
|    | |__| (_| |    |
|     \____\__,_|    |
|                    |
|       Calcium      |
|       40.08 u      |
+--------------------+

Electron Configuration: [Ar]4s2
Electronegativity:      1
Atomic Radius:          231 pm
Ionization Energy:      6.113 eV
Electron Affinity:      
Oxidation States:       2
Standard State:         Solid
Melting Point:          1115 K
Boiling Point:          1757 K
Density:                1.54 g/cm3
Family:                 Alkaline earth metal
Year Discovered:        Ancient
Number of Neutrons:     20
Number of Protons:      20
Number of Electrons:    20
Number of Valence:      2
Valency:                2
Group:                  2
Period:                 4
Shell:                  s-shell
Specific Heat:          0.647 J/g K
Radioactive:            0
Occurrence:             Natural
Source:                 Dying high-mass stars
Source:                 White dwarf supernovae