Compare the chemical elements lithium, beryllium and boron.
| November 14, 2020 | Education
| 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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