Question

although boron(B)is smaller in size than barellium (Be).But 1st ionisation enthalpy of barellium (B) is higher than boron (B) ?

Answer 1

We know half filled and full filled orbitals are stable.

Be: 1s2, 2s2

B: 1s2, 2s2, 2p1

Thus, B will be stable removing an electron. But Be is already stable as it has ful fulled orbital s2. After removal of one electron it will also go to a half filled orbital s1 though, yet Be has higher ionisation energy than B.

Answer 2

Hey there !!!!!

Berilium (Be) has electronic configuration of = 1s²2s²

Boron (B) has electronic configuration of = 1s²2s²2p¹

Element with completely filled orbitals or half-filled orbitals will have higher ionisation potential 

As Be has completely filled 2s orbital 

1st Ionisation evergy of Be > 1st ionisation energy of B

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Hope this helped you.........................