The shell structure of an atom starts with an s subshell in shell 1. The s subshell can hold 2 electrons. Helium atoms have 2 electrons. They can either both go in the 1s shell, or one could go into the next shell, no 2 and into its 2s subshell. However, the 2s subshell requires more energy to fill than the remaining slot in the 1s shell, so the electrons will be paired in the 1s subshell. The atom can be excited by external energy, however and that will excite one or both electrons into the next shell. However, that is no a stable state.
Energy flow through an ecosystem.
Common sites of amputation. (A) Upper extremities. (B) Lower extremities. The surgeon determines th
A turbocharger uses some of the heat energy that would normally be wasted.
People using walkers typically have a high level of mobility impairment.
Endocrine regulation of food intake and energy homeostasis in mammals
China has relied on cheap coal to meet its demand for energy