Each nuclet correlates to valence. The variation is caused by the fact that there are 2 rings available in a Be nuclet, but can 'make do' with one connection. there is some variation allowed apparently.

Lithium - 7 protons (element) / 6 protons nuclet - valence +1

Beryllium - 9 protons (element) / 8 protons nuclet - valence +1 / +2

Boron - 10/11 protons (element) / 9/10 protons nuclet - valence +2 / +3

Carbon - 12 protons (element) / 11 protons nuclet - valence +2 / +4

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Carbon can be -4 in stead of +4 as well, this is where the valence goes negative!

Lacking neutral endings are representative of negative valance such as Oxygen. Further on in the periodic table the it tends to become positive also. (half C nuclet ending tends to be + 2 and not -2

Carbon 12 - no neutral ending - valence -4

Nitorgen 14 (12 + 2) - 1 neutral endings - valence -3

Oxygen 16 (12 + 2 + 2) - 2 neutral endings - valence -2

Fluorine 19 (12 + 5 + 2 - 1 neutral 5 ending (complete) 1 neutral ending - valence -1

Neon  20 (12 + 2 + 2 + 2 + 2) or 22 (12 + 5 + 5) - 4 neutral or 2 complete neutral endings - valence 0