Question

form the symbol 4/2he from the elements Helium write down the mass number of atomic number of the elements​

Answer 1

Answer:

Discovery date 1895

Discovered by Sir William Ramsay in London, and independently by Per Teodor Cleve and Nils Abraham Langlet in Uppsala, Sweden

Origin of the name The name is derived from the Greek, 'helios' meaning sun, as it was in the sun's corona that helium was first detected.

Allotropes -

He

Helium

2 4.003

Fact box

Group 18 Melting point Unknown

Period 1 Boiling point −268.928°C, −452.07°F, 4.222 K

Block s Density (g cm−3) 0.000164

Atomic number 2 Relative atomic mass 4.003

State at 20°C Gas Key isotopes 4He

Electron configuration 1s2 CAS number 7440-59-7

ChemSpider ID 22423 ChemSpider is a free chemical structure database