POTASSIUM Metal ions often exhibit various colors  when vaporized in a flame. This photo shows a flame test for potassium, which  exhibits a violet color.

Physical Properties

Atomic Number: 19
Mass Number: 39.0983
Electron Configuration: 1s²2s²2p⁶3s²3p⁶4s²
Crystal Structure: Body-Centered Cubic
Density: 0.86 g/cm³
Melting Point: 64^oC
First Ionization Energy: 419 kJ/mol
Atomic Radius: 227 pm
Ionic Radius: 133 pm
Standard Reduction Potential: -2.93 V (K⁺ + e^- = K)