For #B#, #Z=5#, i.e. its nucleus contains 5 protons, 5 positively charged, massive particles. And if there 5 protons, the neutral atom has 5 electrons conceived to whiz about the nuclear core, with a formal #1s^(2)2s^(2)2p^1# configuration.
There are 2 common isotopes of boron: (i) #""^11B# contains 6 neutrons, and is approx. 80% naturally abundant; and (ii) #""^10B# with 5 neutrons, makes up the balance. The atomic mass of boron quoted on the Periodic Table, #10.81*g#, reflects this isotopic abundance.
Most of the time, boron forms #BR_3# and #BX_3# compounds, i.e. #B^(III+)#..........it can expand its valence shell to form #BX_4^-# and #BR_4^(-)# derivatives.
