Hydrogen (H)
* Atomic number: 1
* Electron configuration: 1s¹
* Energy levels filled: Only the first energy level (n=1) is filled. The single electron in hydrogen occupies the 1s orbital.
Helium (He)
* Atomic number: 2
* Electron configuration: 1s²
* Energy levels filled: Again, only the first energy level (n=1) is filled. Both helium electrons occupy the 1s orbital.
Key Concepts:
* Energy levels: Electrons in atoms occupy specific energy levels, denoted by the principal quantum number (n). The lowest energy level is n=1, followed by n=2, n=3, and so on.
* Orbitals: Within each energy level are sublevels called orbitals, which describe the probability of finding an electron in a particular region of space. The 1s orbital can hold a maximum of two electrons.
In summary: Both hydrogen and helium have their electrons filling only the first energy level (n=1).
