Lithium is the first element in the second period. The second period has a total number of eight elements in all. The number of electrons in a lithium atom is 3.
The electronic configuration of lithium is 1s²2s¹. Lithium has just a single electron in its outermost shell.
Moving from left to right across the second period, the number of electrons in the outermost shell of the elements increases till it reaches the octet i.e 8:
Be (4) : 1s²2s²
B (5): 1s²2s²2p¹
C (6): 1s²2s²2p²
N (7): 1s²2s²2p³
O(8): 1s²2s²2p⁴
F (9): 1s²2s²2p⁵
Ne(10): 1s²2s²2p⁶
As you go from left to right, the number of valence electrons increases by 1.
From left to right, the number of shell remains fairly constant. Li and Be has one electronic shell each while the rest of the elements in the period have two shells.
