Core electrons shield valence electrons so that they experience an effective nuclear charge zeff rather than the full nuclear charge. given that the first ionization energy of be is 9.32 ev, use the formula en=−z2e2/(8πε0a0n2), n=1,2,3, to estimate the effective nuclear charge experienced by the 2s electron in be. e=1.602×10−19c, me=9.109×10−31kg, ε0=8.854×10−12c2⋅j−1⋅m−1, h=6.626×10−34j⋅s.