1. The problem statement, all variables and given/known data Barium metal crystallizes in a body-centred cubic lattice. The density of the metal is 3.50gcm^-3. Calculate the radius(in pm) of a barium atom. M(Ba)=137.3g/mol , NA = 6.022x10^23/mol 3. The attempt at a solution For 1 unit cell: m=2x137.3/6.022x10^23 =4.56x10^-22g V=m/p =4.56x10^-22/3.5 =1.303x10^8pm^3 Cell side length a=v^(1/3)=506.9pm From here I am confused, the answer is that the cell diagonal length =4r=√3a Atomic radius r=√3/4a=219.5pm Can anyone please explain to me how the cell diagonal length varies with different structures, or anything that can help me, thanks.