103Lr

Lawrencium

Actinideunknownblock f

The last actinide, closing the f-block, and the element whose first ionisation energy was finally measured in 2015 after decades of argument.

Atomic number	103
Mass number (longest-lived isotope)	266 g/mol
This element has no stable isotope, so it has no standard atomic weight. The figure above is the mass number of its longest-lived isotope — a convention, not a measurement of a natural mixture.
Group · period	f-block series · 7
Electron configuration	[Rn] 5f¹⁴ 7s² 7p¹

About Lawrencium

Lawrencium should end the 5f series with a 6d electron, by analogy with lutetium, but relativistic calculations predict the 7p orbital drops below 6d, giving [Rn] 5f¹⁴ 7s² 7p¹ — the only element in the table whose ground state has a p electron where a d one is expected. A Japanese-led team measured its first ionisation energy in 2015 using single atoms in a surface-ionisation apparatus and got 4.96 eV, the lowest of any actinide and in close agreement with the 7p prediction, which is about as direct a confirmation of relativistic quantum chemistry as experiment can offer. Like lutetium, lawrencium has a strong case for sitting in group 3 of the d-block instead; it is kept with the actinides here for layout.

Use 266 g/mol in these solvers

Moles from Mass (n = m/M)

n = \frac{m}{M}

Opens with M = 266 g/mol already filled in

Gas Density from Molar Mass

\rho = \frac{PM}{RT}

Opens with M = 266 g/mol already filled in

Faraday's Law of Electrolysis (m = QM/nF)

m = \frac{Q M}{n F}

Opens with M = 266 g/mol already filled in

Ion Concentration as CaCO₃ Equivalent

C_{\mathrm{CaCO_3}} = C_{\mathrm{ion}} \times \frac{50.04}{\mathrm{EW}}

Opens with EW = 266 g/mol already filled in

Acid Feed to Reduce Alkalinity

\dot m = \frac{\Delta \mathrm{Alk} \, Q \times \frac{\mathrm{EW}}{50.04}}{p/100\%}

Opens with EW = 266 g/mol already filled in

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