Filtering the elements

You will ask the table of the first 20 elements three questions: which elements are alkali metals, how period 3 lines up by size, and what each ionisation enthalpy is in electron volts.

The idea. A filter is df[condition], with conditions joined by & in brackets. sort_values sorts, and a computed column is one line.

Your tasks.

1. Set alkali to the list of symbols in group 1, without hydrogen.
2. Set period3 to the symbols of period 3 that have a radius, smallest atom first.
3. Add a column ie_eV: the ionisation enthalpy divided by $96.49$, rounded to two places.