The periodic table, electron shells, and orbitals
The periodic table
Electron shells and the Bohr model
Electron configurations and the periodic table
- Helium (), neon (), and argon (), as group 18 elements, have outer electron shells that are full or satisfy the octet rule. This makes them highly stable as single atoms. Because of their non-reactivity, they are called the inert gases or noble gases.
- Hydrogen (), lithium (), and sodium (), as group 1 elements, have just one electron in their outermost shells. They are unstable as single atoms, but can become stable by losing or sharing their one valence electron. If these elements fully lose an electron—as and typically do—they become positively charged ions: and .
- Fluorine () and chlorine (), as group 17 elements, have seven electrons in their outermost shells. They tend to achieve a stable octet by taking an electron from other atoms, becoming negatively charged ions: and .
- Carbon (), as a group 14 element, has four electrons in its outer shell. Carbon typically shares electrons to achieve a complete valence shell, forming bonds with multiple other atoms.