Compare the chemical elements lithium, beryllium and boron.

PLAN lithium beryllium boron
serial number; 3 4 five
position in the Periodic Table (period number, group number, subgroup); 2 period,
I group,
main subgroup
2 period,
II group,
main subgroup
2 period,
III group,
main subgroup
the number of protons in the nucleus of an atom; 3 4 five
number of energy levels 2 2 2
total number of electrons; 3 4 five
the number of electrons at the external energy level 1 2 3
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