If it were possible to pack a teaspoon of pure electrons together so that they were touching each other, the weight of the teaspoon would be negligible. Electrons are elementary particles with a very small mass. The mass of an electron is approximately 9.11 x 10^-31 kilograms.
Considering that a teaspoon typically holds a volume of around 5 milliliters, or 5 x 10^-6 cubic meters, and assuming perfect packing with no gaps between electrons, we can calculate the total mass.
The mass of a single electron (9.11 x 10^-31 kilograms) multiplied by the number of electrons in the teaspoon (which can be calculated using Avogadro's number) would give us the total mass. Avogadro's number is approximately 6.022 x 10^23 particles per mole.
Using these values, we can calculate:
Mass of a teaspoon of electrons = (9.11 x 10^-31 kg/electron) x (6.022 x 10^23 electrons/mole) x (5 x 10^-6 m³) = approximately 2.75 x 10^-4 grams
As you can see, the mass of a teaspoon of packed electrons would be extremely small, less than a milligram. In practical terms, it would be difficult to measure such a tiny mass.