- Both are light metals. Beryllium has an atomic weight of 9.0122, while lithium has an atomic weight of 6.941. This makes them the two lightest metals on the periodic table.

- Both have a valence of 1. This means that they both have one electron in their outer shell that is available for bonding.

- Both are highly reactive. Beryllium and lithium are both highly reactive metals, meaning that they readily react with other elements. This is because they have a low ionization energy, which means that it is easy for them to lose their valence electron.

- Both form basic oxides. When beryllium and lithium react with oxygen, they form basic oxides. This is because they have a low electronegativity, which means that they do not attract electrons very strongly.

- Both are used in batteries. Beryllium and lithium are both used in batteries because they have a high electrochemical potential. This means that they can produce a lot of electricity when they are used in a battery.

- Both are rare metals. Beryllium and lithium are both rare metals, meaning that they are not found in abundance in the Earth's crust. This makes them more expensive than other metals.

- Both are toxic. Beryllium and lithium are both toxic metals, meaning that they can cause health problems if they are ingested, inhaled, or absorbed through the skin.