Default: Be, Mg, Ca, Sr, Ba, Ra respectively.

Molecules:

• Neutral atoms: 2 bonds are accepted.

• Charged atoms: Each added charge decreases by one the number of possible bonds.

• Radical: Each added radical decreases by one the number of possible bonds

Ions:

• Be²⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺ Ra²⁺ are accepted

Radicals: ·Me⁺ is accepted