Ba 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰5p⁶6s² → [Xe]6s²
Ba - 2e⁻ → Ba⁺² [Xe]
The mass in a chemical reaction remains (mostly) the same.
(except for radiation/nuclear fission, in which mass gets converted into energy)
They combine with oxygen atoms, I think.
Hydrogen and Helium are the first 2 elements
