The chemical element forms the highest oxide E2O, the molar mass of which is 30 g / mol.

The chemical element forms the highest oxide E2O, the molar mass of which is 30 g / mol. Name this element and describe its position in the periodic system.

Given:
M (E2O) = 30 g / mol

To find:
E -?

Decision:
1) Using the periodic system of D.I.Mendeleev, calculate the atomic mass of an unknown chemical element:
M (E2O) = Mr (E2O) = Ar (E) * N (E) + Ar (O) * N (O);
30 = Ar (E) * 2 + 16 * 1;
Ar (E) = 7;
2) Unknown chemical element – Li – lithium;
3) Lithium is located in group I (previously – the main subgroup of group I), in the second period of the periodic system of D. I. Mendeleev, atomic number – 3; alkali metal.

Answer: Unknown chemical element – Li – lithium.